Cell BiologyCell Biology

Achievement Standard 2.8Achievement Standard 2.8

9046490464

CellsCells

• All living things are made up of 1 or All living things are made up of 1 or more cellsmore cells

• Cells vary in shape but they are always Cells vary in shape but they are always smallsmall

• Small size is due to difficulty in diffusing Small size is due to difficulty in diffusing substancessubstances

• Cells can be divided into 2 types:Cells can be divided into 2 types:– Prokaryotes– Eukaryotes

Cell OrganellesCell Organelles• There are some organelles in cells that are present in both There are some organelles in cells that are present in both

plant and animal cells, and others that are present only in plant and animal cells, and others that are present only in one or the otherone or the other– Cell wall (plant only)Cell wall (plant only)– Cell membraneCell membrane– CytoplasmCytoplasm– Nuclear membraneNuclear membrane– NucleusNucleus– ChromosomesChromosomes– MitochondriaMitochondria– Chloroplast (plant only)Chloroplast (plant only)– CentrioleCentriole– VacuoleVacuole– RibosomeRibosome– Endoplasmic reticulum (smooth and rough)Endoplasmic reticulum (smooth and rough)– LysosomeLysosome– Golgi bodyGolgi body

Nucleus

Nucleus contains inherited information: The total collection of genes located on chromosomes in the nucleus has the complete instructions for constructing a total organism.

Cytoplasm: The nucleus

controls cell metabolism; the

many chemical reactions that

keep the cell alive and

performing its designated role.

Nuclear pores are involved in the active transport of substances into and out of the nucleus

Nucleolus is involved in

the construction of

ribosomes

Nuclear membraneencloses the nucleus in eukaryotic cells

Chromosomes are made up of

DNA and protein and store the

information for controlling the

cell

Structure of the nucleus

Eukaryotes have two types of Eukaryotes have two types of

organelles with their own DNA:organelles with their own DNA:

mitochondriamitochondria

chloroplastschloroplasts

The DNA of these organelles is The DNA of these organelles is

replicated when the organelles are replicated when the organelles are

reproduced (independently of the reproduced (independently of the

DNA in the nucleus).DNA in the nucleus).

Mitochondrion

Ribosome

Mitochondrial DNA

Chloroplast

Chloroplast DNA

Unicellular OrganismsUnicellular Organisms

• Unicellular organisms carryout all their life functions Unicellular organisms carryout all their life functions inside a inside a single single cell. While some of their organelles are cell. While some of their organelles are the same as that of eukaryotes there are some that are the same as that of eukaryotes there are some that are found only in unicellular organisms. These are:found only in unicellular organisms. These are:– Oral Groove – Ciliated channel on one side of the cell where Oral Groove – Ciliated channel on one side of the cell where

food particles are taken infood particles are taken in– Anal Pore – Specialised region of the cell surface where food Anal Pore – Specialised region of the cell surface where food

vacuoles attach an rupture to the outsidevacuoles attach an rupture to the outside– Eyespots – Is used in light detection and phototaxic Eyespots – Is used in light detection and phototaxic

responsesresponses– Contractile Vacuoles – used to regulate the amount of water Contractile Vacuoles – used to regulate the amount of water

inside the organism by expelling it to the outsideinside the organism by expelling it to the outside– Food Vacuole – space that contained ingested food particlesFood Vacuole – space that contained ingested food particles– Pseudopodia – false legs to aid in ingestion of food particlesPseudopodia – false legs to aid in ingestion of food particles

Unicellular Organisms cont..Unicellular Organisms cont..

• As well as having specialised organelles, some of the As well as having specialised organelles, some of the cellular processes are significantly different to those of cellular processes are significantly different to those of multicellular organisms.multicellular organisms.– Gas ExchangeGas Exchange

This is usually by diffusion across the cell membrane. To increase This is usually by diffusion across the cell membrane. To increase efficiency, the organism is usually long and/or flat in shape efficiency, the organism is usually long and/or flat in shape increasing the surface area to volume ratio.increasing the surface area to volume ratio.

– Ingestion and FeedingIngestion and FeedingAll unicellular organisms that cannot photosynthesise must ingest All unicellular organisms that cannot photosynthesise must ingest small food particles as their food supply. Food particles cross the small food particles as their food supply. Food particles cross the membrane by phagocytosis to form a food vacuole which is membrane by phagocytosis to form a food vacuole which is digested. Any indigestible material left in the food vacuole is digested. Any indigestible material left in the food vacuole is discharged to the outside through the anal pore.discharged to the outside through the anal pore.Some unicellular organisms do not have an oral groove so they use Some unicellular organisms do not have an oral groove so they use pseudopodia to engulf the food particles.pseudopodia to engulf the food particles.

– ExcretionExcretionIn unicellular organisms, the main waste product formed is In unicellular organisms, the main waste product formed is ammonia. This is very toxic so it must be diluted by large volumes ammonia. This is very toxic so it must be diluted by large volumes of water before being excreted. Contractile vacuoles aid in the of water before being excreted. Contractile vacuoles aid in the collection and removal of wastes. collection and removal of wastes.

Unicellular Organisms cont..Unicellular Organisms cont..– Water regulationWater regulation

Since many unicellular organisms live in fresh water and are Since many unicellular organisms live in fresh water and are enclosed by semi-permeable membranes water is constantly enclosed by semi-permeable membranes water is constantly moving into them. Contractile vacuoles work to collect and moving into them. Contractile vacuoles work to collect and remove the water to ensure the cell does not burst.remove the water to ensure the cell does not burst.

– LocomotionLocomotionFor some unicellular organisms locomotion is achieved by the For some unicellular organisms locomotion is achieved by the coordinated beating of cilia, others use flagella and Amoeba coordinated beating of cilia, others use flagella and Amoeba use the pseudopodia to move.use the pseudopodia to move.

– Responses to External StimuliResponses to External StimuliMost movement is a response to changes in the protoplasmic Most movement is a response to changes in the protoplasmic contents of the organism. Some organisms have eyespots contents of the organism. Some organisms have eyespots that detect the amount of visible light and trigger a that detect the amount of visible light and trigger a phototaxic response.phototaxic response.

– ReproductionReproductionThis can be asexual via binary fission or, vary rarely, sexually This can be asexual via binary fission or, vary rarely, sexually through the exchange of genetic materialthrough the exchange of genetic material

Bacteria have no membrane-Bacteria have no membrane-

bound organelles.bound organelles.

Cellular reactions occur on the Cellular reactions occur on the

inner surface of the cell inner surface of the cell

membrane or in the cytoplasm.membrane or in the cytoplasm.

Bacterial DNA is found in:Bacterial DNA is found in:

One, large circular One, large circular

chromosomechromosome..

Several small chromosomal Several small chromosomal

structures called structures called plasmidsplasmids..

Flagellum

Cell wall

Single, circularchromosome

Cytoplasm(no nucleus)

Cell membrane

Plasmids

Ribosomes

Cell ProcessesCell Processes

Cell MembraneCell Membrane• Surrounds the cell and keeps it separate from the outside Surrounds the cell and keeps it separate from the outside

mediummedium• Semi-permeable membrane that controls what goes in and outSemi-permeable membrane that controls what goes in and out• In animal cells, it is the outside layer but in plants the cell wall In animal cells, it is the outside layer but in plants the cell wall

surrounds itsurrounds it

• Membrane is called a lipid bi-layer consisting of two hydrophillic Membrane is called a lipid bi-layer consisting of two hydrophillic heads on the outside and hydrophobic tails on the insideheads on the outside and hydrophobic tails on the inside

• The general structure is based on the The general structure is based on the fluid mosaic modelfluid mosaic model..

Fatty acidtails

Protein

PoreGlycerol-phosphateheads

Cell TransportCell Transport

• Materials such as ions, water, Materials such as ions, water, molecules and nutrients are molecules and nutrients are transported within cells and in and out transported within cells and in and out of cells by processes which are either of cells by processes which are either passivepassive or or active.active.

Diffusion ThroughBi-layer

Facilitateddiffusion

Passive TransportPassive Transport

• This does not require energyThis does not require energy

• It can be separated into 2 types:It can be separated into 2 types:– DiffusionDiffusion– OsmosisOsmosis

DiffusionDiffusion

• The net movement of particles from an area of The net movement of particles from an area of high concentration to an area of low conentration.high concentration to an area of low conentration.

• Difference between the two areas is the Difference between the two areas is the concentration gradientconcentration gradient

• A large difference=large gradient=faster diffusionA large difference=large gradient=faster diffusion

• The rate of diffusion varies depending on:The rate of diffusion varies depending on:• Size of moleculesSize of molecules

• Temperature of substanceTemperature of substance

• State of matterState of matter

• Concentration of chemicalsConcentration of chemicals

• The cell membrane may contain proteins that help The cell membrane may contain proteins that help facilitate diffusionfacilitate diffusion

Osmosis Osmosis http://www.tvdsb.on.ca/WESTMIN/science/sbi3a1/cells/Osmosis.htm

• The net movement of water from a high The net movement of water from a high concentration to a low concentration through a concentration to a low concentration through a semi-permeable membranesemi-permeable membrane

• Solution with not much water: Solution with not much water: hypertonichypertonic

• Solution with lots of water: Solution with lots of water: hypotonichypotonic

• Solution with the same water concentration: Solution with the same water concentration: isotonicisotonic

Active TransportActive Transport

• Movement against a concentration Movement against a concentration gradient, ie from a low concentration gradient, ie from a low concentration to a high concentrationto a high concentration

• It requires energy so:It requires energy so:•Heat is given offHeat is given off•Oxygen is used upOxygen is used up•COCO22 produced produced•Glucose used upGlucose used up

• Two main types:Two main types:•EndocytosisEndocytosis•ExocytosisExocytosis

EndocytosisEndocytosis

• Taking particles Taking particles intointo a cell.a cell.

• Engulfing a liquid = Engulfing a liquid = pinocytosispinocytosis

• Engulfing a solid = Engulfing a solid = phagocytosisphagocytosis

ExocytosisExocytosis

• Occurs when vacuoles expel their Occurs when vacuoles expel their contents to the outsidecontents to the outside

Amino AcidsAmino AcidsAmino acids are linked together to form Amino acids are linked together to form proteinsproteins..

All amino acids have the same general structure, but each type differs from the All amino acids have the same general structure, but each type differs from the

others by having a unique others by having a unique ‘R’ group‘R’ group..

The ‘R’ group is the variable part of the amino acid.The ‘R’ group is the variable part of the amino acid.

2020 different amino acids are commonly found in proteins. different amino acids are commonly found in proteins.

Example of an amino

acid shown as a space

filling model: Cysteine

Symbolic formula

Amine group

Carboxyl group makes the molecule behave like a weak acid

Carbon atom

Hydrogen atom

The 'R' group varies in chemical make-up with each type of amino

acid

Types of Amino AcidTypes of Amino Acid

Amino acids with different types of Amino acids with different types of ‘R’ ‘R’ groupsgroups have different have different chemicalchemical properties: properties:

Acidic

Aspartic acid(acidic)

Forms di-sulfide bridges that

can link to similar amino acids

Cysteine(forms di-sulfide bridges)

Basic

Lysine(basic)

Polypeptide ChainsPolypeptide Chains

Amino acids are liked together in long chains by the Amino acids are liked together in long chains by the formation of formation of peptide bondspeptide bonds..

Long chains of such amino acids are called Long chains of such amino acids are called polypeptide chainspolypeptide chains..

Polypeptide chain

Peptidebond

Peptidebond

Peptidebond

Peptidebond

Peptidebond

Peptidebond

FunctionFunction ExamplesExamples

StructuralStructural Forming the structural Forming the structural components of organscomponents of organs Collagen, keratinCollagen, keratin

RegulatoryRegulatory Regulating cellular function Regulating cellular function (hormones)(hormones)

Insulin, glucagon, adrenalin, Insulin, glucagon, adrenalin, human growth hormone, human growth hormone, follicle stimulating hormonefollicle stimulating hormone

ContractileContractile Forming the contractile Forming the contractile elements in muscleselements in muscles Myosin, actinMyosin, actin

ImmunologicImmunologicalal

Functioning to combat Functioning to combat invading microbesinvading microbes

antibodies such as antibodies such as GammaglobulinGammaglobulin

TransportTransport Acting as carrier moleculesActing as carrier molecules Hemoglobin, myoglobinHemoglobin, myoglobin

CatalyticCatalytic Catalyzing metabolic reactions Catalyzing metabolic reactions (enzymes)(enzymes)

amylase, lipase, lactase, amylase, lipase, lactase, trypsintrypsin

Protein FunctionProtein Function

Proteins can be classified according to Proteins can be classified according to their their functional rolefunctional role in an organism: in an organism:

Hemoglobin

Protein StructureProtein StructureThe production of a functional protein The production of a functional protein requires that the polypeptide chain assumes requires that the polypeptide chain assumes a precise structure comprising several levels:a precise structure comprising several levels:

Primary structure: Primary structure: The sequence of The sequence of amino acids in a polypeptide chain. amino acids in a polypeptide chain.

Secondary structure: Secondary structure: The The shapeshape of of the polypeptide chain (e.g. alpha-the polypeptide chain (e.g. alpha-helix).helix).

TertiaryTertiary structure: structure: The The overall overall conformationconformation (shape) of the (shape) of the polypeptide caused by folding.polypeptide caused by folding.

QuaternaryQuaternary structurestructure: In some : In some proteins, an additional level of proteins, an additional level of organization groups separate organization groups separate polypeptide chains together to formpolypeptide chains together to forma a functionalfunctional protein.protein.

Hemoglobin molecule

Beta chain

Alpha chainBeta chain

Alpha chain

Amino acid

Di-sulfide bridge

EnzymesEnzymes

• Enzymes are Enzymes are biological catalystsbiological catalysts, regulating cell , regulating cell metabolism.metabolism.

• An enzyme acts on a molecule called the An enzyme acts on a molecule called the substratesubstrate..• Enzymes are specific for the reactions they catalyze. Enzymes are specific for the reactions they catalyze. • Enzyme activity depends on the enzyme’s shape and Enzyme activity depends on the enzyme’s shape and

its its active siteactive site (the binding site for the substrate). (the binding site for the substrate).• Enzymes are often named for the substrate on which Enzymes are often named for the substrate on which

they work, and sometimes include the suffix -ase:they work, and sometimes include the suffix -ase:– Lipase Lipase breaks down fats (lipids)breaks down fats (lipids)– Amylase Amylase breaks down starch (amylose/amylopectin)breaks down starch (amylose/amylopectin)– Lactase Lactase breaks down milk sugar (lactose)breaks down milk sugar (lactose)– Cholinesterase Cholinesterase breaks down the neurotransmitter breaks down the neurotransmitter

acetylcholine in the nervous systemacetylcholine in the nervous system

Enzyme StructureEnzyme StructureRibonuclease SRibonuclease S (right) is an (right) is an

enzyme that breaks up RNA enzyme that breaks up RNA

molecules.molecules.

The The redred areas designate the areas designate the

active site and comprise active site and comprise

certain amino acid 'R' groups.certain amino acid 'R' groups.

The The substratesubstrate (in this case, (in this case,

RNA) is drawn into the active RNA) is drawn into the active

site, putting the substrate site, putting the substrate

molecule under stress, thereby molecule under stress, thereby

causing the reaction to causing the reaction to

proceed more readily.proceed more readily.

RNA

Active sites are

attraction points that

draw the substrate to

the surface of the

enzyme

The substrate is

the chemical that

an enzyme acts on

Enzymes are specific catalysts. The

complexity of the active site makes each

enzyme specific for the substrate it acts on.

Functional EnzymeFunctional Enzyme• Ribonuclease SRibonuclease S (right) is an enzyme (right) is an enzyme

that breaks up RNA molecules.that breaks up RNA molecules.• The The redred areas designate the active areas designate the active

site and comprise certain amino acid site and comprise certain amino acid 'R' groups.'R' groups.

• The The substratesubstrate (in this case, RNA) is (in this case, RNA) is drawn into the active site, putting the drawn into the active site, putting the substrate molecule under stress, substrate molecule under stress, thereby causing the reaction to thereby causing the reaction to proceed more readily.proceed more readily.

• Nearly all enzymes are made of Nearly all enzymes are made of protein, although RNA can also have protein, although RNA can also have enzymic properties.enzymic properties.

• Some enzymes contain only protein.Some enzymes contain only protein.• Others, called Others, called conjugated protein conjugated protein

enzymesenzymes, require additional , require additional components to complete their components to complete their catalytic properties.catalytic properties.– These may be permanently attached These may be permanently attached

parts called parts called prosthetic groupsprosthetic groups, or , or temporarily attached non-protein temporarily attached non-protein coenzymescoenzymes, which detach after a , which detach after a reaction and may then participate reaction and may then participate with another enzyme in other with another enzyme in other reactions.reactions.

Coenzyme is

required for function

Prosthetic group is

required for function

Conjugated Protein Enzymes

Protein-only Enzymes

Active site

Enzyme

Enzyme comprising only protein

e.g. lysozyme

Prosthetic group

Apoenzyme

Coenzyme

Apoenzyme

Conjugated Protein EnzymesConjugated Protein Enzymes

Coenzyme requiredContains the apoenzyme (protein)

plus a coenzyme (non-protein)e.g. Dehydrogenases + NAD

Prosthetic group requiredContains the apoenzyme

(protein) plus a prosthetic groupe.g. Flavoprotein + FAD

The prosthetic group remains more or less permanently attached

Apoenzyme alone is inactive

Active site

The coenzyme becomes detached from the apoenzyme after the reaction and may go on participate in further reactions

Active site

Apoenzyme

Mechanism of Enzyme Mechanism of Enzyme ActionAction

• The specificity of The specificity of the substrate is the substrate is determined by determined by the complexity of the complexity of the binding sites.the binding sites.

• The wrong The wrong substrates will substrates will not fit into the not fit into the active site.active site.

• Some enzymes Some enzymes have specificity have specificity to a bond type to a bond type (e.g. lipases (e.g. lipases break up any break up any chain length of chain length of lipid).lipid).

Steps in Enzyme ActivityIn the induced fit model of enzyme function, the enzyme fits to its substrate somewhat like a lock and key, with the shape of the enzyme changing when the substrate fits into the cleft of the active site.

Cleft

Substrate moleculesTwo substrate molecules

are drawn into the cleft of

the enzyme’s active site Enzyme

Enzyme changes shapeEnzyme

The shape of the

enzyme’s active site is

modified by its interaction

with the substrate(s). The

shape changes force the

substrate molecules to

combine.

End product is released

Enzyme

The resulting end product

is released by the

enzyme, which returns to

its normal shape, ready to

receive more substrate.

Enzymes are CatalystsEnzymes are Catalysts• Catalysts are substances that Catalysts are substances that

increase the rate of chemical increase the rate of chemical reactions. All catalysts speed reactions. All catalysts speed up reactions by:up reactions by:– Influencing the stability of Influencing the stability of

bonds in the reactants.bonds in the reactants.– Providing an alternative Providing an alternative

reaction pathway; the binding reaction pathway; the binding of reactants and enzyme can of reactants and enzyme can weaken bonds in the weaken bonds in the reactants and allow the reactants and allow the reaction to proceed more reaction to proceed more easily.easily.

• Enzymes are biologicalEnzymes are biologicalcatalystscatalysts; they alter the ; they alter the chemical equilibrium between chemical equilibrium between

the reactant and the product.the reactant and the product.• When the substrate attains When the substrate attains

the required energy it is able the required energy it is able to change into the product or to change into the product or products.products.

Direction of reactionFinish

Product

Reactant

Am

ount

of e

nerg

y st

ored

in th

e ch

emic

als

LowStart

Without enzyme

High energy

Low energy

With enzyme

High

Enzymes are CatalystsEnzymes are Catalysts

Low

Direction of reaction

Finish

Am

ount

of e

nerg

y st

ored

in th

e ch

emic

als

High

Start

With enzyme present, the

energy required for the

reaction to proceed is reduced

(the activation energy is

lower). Reactants turn into

products more readily.

Without enzyme present, the energy needed

to make the reaction proceed in the forward

direction (the activation energy) is very high.

Product

Reactant

High energy

Low energy

Catalysts provide an alternative pathway of lower activation energy.

Effects of pH on EnzymesEffects of pH on Enzymes• Like all proteins, Like all proteins,

enzymes are enzymes are denatured (made non-denatured (made non-functional) by functional) by extremes of pH extremes of pH (acid/alkaline).(acid/alkaline).

• Within these extremes Within these extremes most enzymes are still most enzymes are still influenced by pH.influenced by pH.

• There is a particular pH There is a particular pH for optimum activity for optimum activity for each enzyme. This for each enzyme. This is because the active is because the active sites of the enzyme sites of the enzyme can be disabled by the can be disabled by the wrong pH.wrong pH.

AlkalineAcidpH

Enz

yme

act

ivity

Optimum pH

for urease

Optimum pH

for trypsin

Urease

Pepsin

Trypsin

Optimum pH

for pepsin

Temperature and Enzyme Temperature and Enzyme ActivityActivity

• Reactions occur faster Reactions occur faster at higher at higher temperatures, but the temperatures, but the rate of denaturation of rate of denaturation of enzymes also increases enzymes also increases at higher at higher temperatures.temperatures.

• High temperatures High temperatures break the disulfide break the disulfide bonds important for the bonds important for the tertiary structure of the tertiary structure of the enzyme.enzyme.

• This destroys the active This destroys the active sites and therefore sites and therefore makes the enzyme makes the enzyme non-functional.non-functional.

Rapid denaturation

Temperature (°C)

Enz

yme

act

ivity

Too cold for the enzyme to

operate

Optimum temperature for enzyme

Enzyme Concentration And Enzyme Concentration And Enzyme ActivityEnzyme Activity

• Assuming that the Assuming that the amount of substrate is amount of substrate is not limiting, an increase not limiting, an increase in enzyme in enzyme concentration causes concentration causes an increase in the an increase in the reaction rate.reaction rate.

• Cells may increase the Cells may increase the amount of enzyme amount of enzyme present by increasing present by increasing the rate of its synthesis the rate of its synthesis to meet demand.to meet demand.

With ample substrate and cofactors present

Rat

e o

f re

actio

n

Enzyme concentration

Substrate Concentration Effect Substrate Concentration Effect on Enzyme Activityon Enzyme Activity• Assuming that the Assuming that the

amount of enzyme is amount of enzyme is constant and non-constant and non-limiting, an increase in limiting, an increase in substrate concentration substrate concentration causes a diminishing causes a diminishing increase in the reaction increase in the reaction rate.rate.

• A maximum rate is A maximum rate is obtained at a certain obtained at a certain substrate concentration substrate concentration where all enzymes are where all enzymes are occupied by substrate. occupied by substrate. The reaction rate The reaction rate cannot increase further.cannot increase further.

With ample enzyme

and cofactors present

Substrate concentration

Rat

e of

rea

ctio

n

Effect of Cofactors on Effect of Cofactors on EnzymesEnzymes• Cofactors are substances Cofactors are substances

that are essential to the that are essential to the catalytic activity of some catalytic activity of some enzymes. enzymes.

• Cofactors may alter the Cofactors may alter the shape of enzymes slightly to shape of enzymes slightly to make the active sites make the active sites functional or to complete the functional or to complete the reactive site.reactive site.

• Enzyme cofactors can be Enzyme cofactors can be inorganic, e.g. metal ions inorganic, e.g. metal ions and iron-sulfur clusters, or and iron-sulfur clusters, or organic compounds, which organic compounds, which are known as are known as coenzymescoenzymes..

• Many vitamins are Many vitamins are coenzymes. Vitamins are coenzymes. Vitamins are organic molecules not organic molecules not synthesized by the body, e.g. synthesized by the body, e.g. vitamin K, B1, B6, and folate.vitamin K, B1, B6, and folate.

Once the shape of the enzyme has been modified by the cofactor, substrates A and B can react together.

ProductThe presence of the cofactor alters the shape of the enzyme

Enzyme

Enzyme InhibitionEnzyme Inhibition• Enzyme inhibitorsEnzyme inhibitors are are

substances that prevent the substances that prevent the normal action of an enzyme normal action of an enzyme and thereby slow the rate of and thereby slow the rate of enzyme controlled reactions.enzyme controlled reactions.

• Enzyme inhibitors may or Enzyme inhibitors may or may not act reversibly.may not act reversibly.

• In In reversible inhibitionreversible inhibition, , the inhibitor is temporarily the inhibitor is temporarily bound to the enzyme, bound to the enzyme, thereby preventing its thereby preventing its function.function.– Reversible inhibition is often a Reversible inhibition is often a

means by which enzyme means by which enzyme activity activity is regulated in the functioning is regulated in the functioning cell.cell.

• In In irreversible inhibitionirreversible inhibition, , the inhibitor (poison) may the inhibitor (poison) may bind permanently to the bind permanently to the enzyme and cause it to be enzyme and cause it to be permanently deactivated.permanently deactivated.

Insecticides and heavy

metals, such as mercury,

are poisons that inhibit

enzyme activity.

Reversible InhibitionReversible Inhibition• Reversible inhibitors are used Reversible inhibitors are used

to control the activity of to control the activity of enzymes.enzymes.

• There is often an interaction There is often an interaction between the substrate or end between the substrate or end product and the enzyme product and the enzyme controlling the reaction.controlling the reaction.

• Buildup of the end product or a Buildup of the end product or a lack of substrate may lack of substrate may deactivate the enzyme. This deactivate the enzyme. This deactivation can occur via deactivation can occur via competitivecompetitive or or noncompetitive inhibitionnoncompetitive inhibition..– Competitive inhibitorsCompetitive inhibitors

compete with the substrate for compete with the substrate for the active site.the active site.

– Noncompetitive inhibitorsNoncompetitive inhibitors bind to the enzyme, but not at bind to the enzyme, but not at the active site. The substrate the active site. The substrate can bind but enzyme function can bind but enzyme function is impaired.is impaired.

– AllostericAllosteric inhibitorsinhibitors are non are non competitive inhibitorscompetitive inhibitorsthat prevent the substrate from that prevent the substrate from binding.binding.

Model of elastase and its inhibitor

Competitive InhibitionCompetitive Inhibition• Competitive inhibitors Competitive inhibitors

compete with the compete with the substrate for the active substrate for the active site, thereby blocking it site, thereby blocking it and preventing its and preventing its attachment to the attachment to the substrate.substrate.

• The inhibition is reversible.The inhibition is reversible.– Example: Malonate is a Example: Malonate is a

powerful inhibitor of cellular powerful inhibitor of cellular respiration because it is a respiration because it is a competitive inhibitor of the competitive inhibitor of the enzyme succinate enzyme succinate dehydrogenase in the Krebs dehydrogenase in the Krebs cycle, which catalyzes the cycle, which catalyzes the oxidation of succinate to oxidation of succinate to fumarate.fumarate.

Good fit

Substrate

Enzyme

No inhibition

Competitive inhibitor blocks the active site

Substrate

Competitive inhibitore.g. malonate

Enzyme

Non-Competitive InhibitionNon-Competitive Inhibition• Non-competitive Non-competitive

inhibitorsinhibitors bind to the bind to the enzyme, but not at the enzyme, but not at the active site, and alter its active site, and alter its shape. The substrate is shape. The substrate is still able to bind, but the still able to bind, but the reaction rate is slowed reaction rate is slowed because the enzyme is because the enzyme is less able to perform its less able to perform its function.function.

• AllostericAllosteric enzyme enzyme inhibitorsinhibitors are non are non competitive inhibitorscompetitive inhibitors that induce a shape that induce a shape change that alters the change that alters the active site and prevents active site and prevents the substrate from the substrate from binding.binding.– In this case, the enzyme In this case, the enzyme

ceases to function.ceases to function.

Good fit

Substrate

Enzyme

No inhibition

Allosteric inhibitor

Enzyme

The substrate cannot bind

Non-competitive inhibitor

Active site is distorted

The inhibitor binds to the enzyme, and alters the enzyme’s ability to function properly.

The substrate binds to the active site

Non-competitive inhibitor

Enzyme

Irreversible InhibitionIrreversible Inhibition• Irreversible enzyme inhibitors are Irreversible enzyme inhibitors are

poisons that prevent enzyme poisons that prevent enzyme function.function.

• Heavy metalsHeavy metals: Certain heavy : Certain heavy metals bind tightly and metals bind tightly and permanently to the active sites of permanently to the active sites of enzymes, destroying their catalytic enzymes, destroying their catalytic properties.properties.– Example: Example: mercurymercury (Hg), (Hg), cadmiumcadmium

(Cd), (Cd), leadlead (Pb), and (Pb), and arsenicarsenic (As). (As).– They are generally non-competitive They are generally non-competitive

inhibitors, although an exception is inhibitors, although an exception is mercurymercury which deactivates the which deactivates the enzyme enzyme papainpapain..

– Heavy metals are retained in the Heavy metals are retained in the body, and lost slowly.body, and lost slowly.

• InsecticidesInsecticides– These can prevent the breakdown These can prevent the breakdown

of of acetylcholine acetylcholine (ACh), a (ACh), a neurotransmitter in the nervous neurotransmitter in the nervous system.system.

– They bind to the enzyme that They bind to the enzyme that normally breaks down the ACh, normally breaks down the ACh, causing over stimulation of the causing over stimulation of the nerves.nerves.

Papain enzyme

Substrate The substrate cannot bind to the active site

The inhibitor blocks the active site Active site

Energy in CellsEnergy in Cells• Every living cell needs a regular supply of Every living cell needs a regular supply of

energy to power chemical processesenergy to power chemical processes• Sources of energy are large complex molecules Sources of energy are large complex molecules

which make up food supplywhich make up food supply• Energy is released when the bonds holding Energy is released when the bonds holding

atoms together are released, usually as heatatoms together are released, usually as heat• Energy is used to form adenosine-tri-phosphate Energy is used to form adenosine-tri-phosphate

(ATP) from adenosine-di-phosphate (ADP)(ATP) from adenosine-di-phosphate (ADP)• ADP = ADP =

• ATP = ATP =

• Photosynthesis Photosynthesis capturescaptures light energy and stores light energy and stores is in food – glucoseis in food – glucose

• Respiration Respiration releasesreleases energy from glucose energy from glucose• Energy is stored at ATP until it is neededEnergy is stored at ATP until it is needed

Adenosine P P

Adenosine P P P

RespirationRespiration• Respiration is a process which makes ATP using energy in Respiration is a process which makes ATP using energy in

organic molecules such as glucose – glycolysis, Kreb’s cycle organic molecules such as glucose – glycolysis, Kreb’s cycle and oxidative phosphorylation (electron transport chain). and oxidative phosphorylation (electron transport chain).

• If glucose is placed in oxygen and set alight, it burns and releases If glucose is placed in oxygen and set alight, it burns and releases a lot of heat energy as the glucose molecules combine with a lot of heat energy as the glucose molecules combine with oxygen to form carbon dioxide and water and the energy from oxygen to form carbon dioxide and water and the energy from glucose is rapidly transferred to heat energy. This is an oxidation glucose is rapidly transferred to heat energy. This is an oxidation reaction.reaction.

• In a living cell, a similar process takes place, but in a more In a living cell, a similar process takes place, but in a more controlled way. You will recognise the equation:controlled way. You will recognise the equation:

Glucose + oxygen Glucose + oxygen energy + carbon dioxide + water energy + carbon dioxide + waterCC66HH1212OO66 + O + O22 energy + CO energy + CO22 + H + H22O O

• This actually happens in a series of reactions controlled by This actually happens in a series of reactions controlled by enzymes and the energy in glucose is released in small stages. A enzymes and the energy in glucose is released in small stages. A sequence of reactions (like in the process of respiration) is called a sequence of reactions (like in the process of respiration) is called a metabolic pathway.metabolic pathway.

Glycolysis – Glycolysis – glucose converted to glucose converted to pyruvatepyruvate

• Occurs in the cytoplasm of the cellOccurs in the cytoplasm of the cell

• Glucose (a 6 carbon compound) is Glucose (a 6 carbon compound) is converted into two pyruvate (pyruvic converted into two pyruvate (pyruvic acid) molecules (a 3 carbon acid) molecules (a 3 carbon compound)compound)

• Small amount of ATP Small amount of ATP (adenosine (adenosine triphosphate) triphosphate) is made in this is made in this process process (2 ATP)(2 ATP)

Kreb Cycle – Kreb Cycle – pyruvate fed into pyruvate fed into cycle of reactionscycle of reactions

• Occurs in the matrix of the mitochondriaOccurs in the matrix of the mitochondria• If oxygen is available, pyruvate (pyruvic acid) If oxygen is available, pyruvate (pyruvic acid)

formed in glycolysis passes into a mitochondrion formed in glycolysis passes into a mitochondrion through the outer and inner membranesthrough the outer and inner membranes

• Link step to convert the pyruvate into a different Link step to convert the pyruvate into a different molecule which then undergoes a cycle of molecule which then undergoes a cycle of reactionsreactions

• Carbon dioxide removed (called decarboxylation) Carbon dioxide removed (called decarboxylation) and diffuses out of the mitochondrion, out of the and diffuses out of the mitochondrion, out of the cell and out of organismcell and out of organism

• 2 ATP2 ATP molecules produced molecules produced• Hydrogen ions (H+ ions) and electrons are also Hydrogen ions (H+ ions) and electrons are also

produced in Kreb’s cycle to be fed into the produced in Kreb’s cycle to be fed into the electron transport chain to make more ATPelectron transport chain to make more ATP

Oxidative Phosphorylation Oxidative Phosphorylation (electron transport chain) -(electron transport chain) - electrons electrons produced passed along an electron transport chain to produced passed along an electron transport chain to produce ATPproduce ATP

• This happens in the inner membrane of the mitochondrionThis happens in the inner membrane of the mitochondrion• ATP is made by the addition of inorganic phosphate Pi to ATP is made by the addition of inorganic phosphate Pi to

ADP. This is called a ADP. This is called a phosphorylation reactionphosphorylation reaction. In . In respiration, this process needs oxygen so it is known as respiration, this process needs oxygen so it is known as oxidative phosphorylation. oxidative phosphorylation. The enzyme ATP synthase The enzyme ATP synthase makes the ATP from ADP + Pimakes the ATP from ADP + Pi

• H+ ions and electrons pass through a series of reactions H+ ions and electrons pass through a series of reactions and energy is released as ATP. At the end of this electron and energy is released as ATP. At the end of this electron transport chain, oxygen is needed. transport chain, oxygen is needed.

• Oxygen at the end of the electron transport chain Oxygen at the end of the electron transport chain combines with electrons and hydrogen ions to form water. combines with electrons and hydrogen ions to form water.

• A lot of ATP is made in this part of respiration (A lot of ATP is made in this part of respiration (34ATP34ATP molecules)molecules)

Anaerobic RespirationAnaerobic Respiration• When oxygen is not available, only When oxygen is not available, only glycolysis glycolysis can occur. Therefore, a can occur. Therefore, a

small amount of ATP is made (2 ATP) along with pyruvatesmall amount of ATP is made (2 ATP) along with pyruvate• Pyruvate will inhibit glycolysis so it is converted to something Pyruvate will inhibit glycolysis so it is converted to something

elseelse. .

SOLUTIONS to remove the pyruvateSOLUTIONS to remove the pyruvate

ALCOHOLIC FERMENTATIONALCOHOLIC FERMENTATION LACTIC FERMENTATIONLACTIC FERMENTATIONUsed by fungi & plantsUsed by fungi & plants Used by animalsUsed by animalsYeast converts pyruvate to ethanolYeast converts pyruvate to ethanol Pyruvate is converted to lactic acidPyruvate is converted to lactic acidGlucose Glucose pyruvate pyruvate ethanol + CO ethanol + CO22 +2 ATP +2 ATP Glucose Glucose pyruvate pyruvate lactic acid +2 lactic acid +2 ATPATP

If yeast is supplied with a supply of If yeast is supplied with a supply of Lactic acid build up in muscles causes the pain Lactic acid build up in muscles causes the pain in in carbohydrate, it will carry out glycolysiscarbohydrate, it will carry out glycolysis exhausted muscles. The lactic acid isexhausted muscles. The lactic acid isand alcoholic fermentation.and alcoholic fermentation. transported in the blood to the liver and heretransported in the blood to the liver and here

it is converted back to pyruvic acid and then it is converted back to pyruvic acid and then to glucose during recovery. to glucose during recovery.

The ethanol is used to make alcoholic drinks.The ethanol is used to make alcoholic drinks.

In baking, the CO 2 is used to make bread, In baking, the CO 2 is used to make bread, This requires oxygen, which is why you This requires oxygen, which is why you etc. riseetc. rise continue breathing deeply after you stop continue breathing deeply after you stop

exercising. You are exercising. You are supplying extra supplying extra oxygen to oxygen to the liver to deal with the lactic acid the liver to deal with the lactic acid produced produced because of a shortage of oxygen because of a shortage of oxygen earlier on. You earlier on. You are paying off an oxygen debtare paying off an oxygen debt

Summary of RespirationSummary of Respiration

PhotosynthesisPhotosynthesis• Inputs – CO2, H2O, lightInputs – CO2, H2O, light

• CO2 is absorbed from air as gasCO2 is absorbed from air as gas• Water absorbed from environmentWater absorbed from environment• Light – red and green light most photosynthetically activeLight – red and green light most photosynthetically active

• Outputs – COutputs – C66HH1212OO66, O, O22• CC66HH1212OO6 6 – glucose temporarily stored as starch in leaves to be – glucose temporarily stored as starch in leaves to be

used in respirationused in respiration• OO22 is essentially a waste product that diffuses out is essentially a waste product that diffuses out

• 6CO6CO22 + 6H + 6H22O O C C66HH1212OO66 + 6O + 6O22

• Occurs in all green plantsOccurs in all green plants• Requires sunlight so leaves broad, thin and flat Requires sunlight so leaves broad, thin and flat

but also prone to water lossbut also prone to water loss• Water loss decreased by waterproof cuticle Water loss decreased by waterproof cuticle

which is a waxy layer on leafwhich is a waxy layer on leaf• Stomata present to allow COStomata present to allow CO22 in and stop water in and stop water

lossloss

• Transfer of Transfer of light energylight energy into into chemical chemical potential energypotential energy

• Occurs in the Occurs in the granagrana of chloroplasts of chloroplasts

• Relied on by all organismsRelied on by all organisms

• Occurs in 2 stagesOccurs in 2 stages•The light phase The light phase

•Dark phase/Light independent phaseDark phase/Light independent phase (Calvin cycle) (Calvin cycle)

• Chlorophyll plays vital role in trapping Chlorophyll plays vital role in trapping light energylight energy

PhotosynthesisPhotosynthesis

Light PhaseLight Phase

Light Independent PhaseLight Independent Phase

PLight Energy

ADP +Chlorophyll

ATP

12H2O 12H2 + 6CO2

(Given off)

To dark phase

Carries Energy

6CO2 + 12H2 C6H12O6 + 6H2O

ChromosomesChromosomes– A: Light microscopeA: Light microscope view of a view of a

chromosomechromosomefrom the salivary glands of the from the salivary glands of the fly fly SimuliumSimulium..• BandingBanding: groups of genes : groups of genes

stained light and dark.stained light and dark.• PuffingPuffing: areas of transcription : areas of transcription

(mRNA production).(mRNA production).– B: Scanning electron B: Scanning electron

microscopemicroscope (SEM) view of sex (SEM) view of sex chromosomes in the condensed chromosomes in the condensed state during astate during acell division. Individual cell division. Individual chromatin fibers are visible.chromatin fibers are visible.• The smaller chromosome is the The smaller chromosome is the

‘Y’ while the‘Y’ while thelarger one is the X.larger one is the X.

– C: Transmission electron C: Transmission electron microscopemicroscope (TEM) view of (TEM) view of chromosomes lined up at the chromosomes lined up at the equator of a cell during the equator of a cell during the process of cell division. These process of cell division. These chromosomes are also in the chromosomes are also in the condensed state.condensed state.

A

B

C

Chromosome StatesChromosome States• InterphaseInterphase: Chromosomes are : Chromosomes are singlesingle--armedarmed

structures during their unwound state during interphase.structures during their unwound state during interphase.• DividingDividing cellscells: Chromosomes are : Chromosomes are doubledouble--armedarmed

structures, having replicated their DNA to form two structures, having replicated their DNA to form two chromatidschromatids in preparation for cell division. in preparation for cell division.

Centromere

Interphasechromosome

This chromosome would

not be visible as a coiled

up structure, but unwound

as a region of dense

chromatin in the nucleus

(as in the TEM of the

nucleus above)

Replicated chromosomeprepared for cell division

Chromatin

Chromatid

Chromatid

Chromosome StructureChromosome Structure• HistoneHistone proteins organize the DNA into proteins organize the DNA into

tightly coiled structures (visible tightly coiled structures (visible chromosomes) during cell division.chromosomes) during cell division.

• CoilingCoiling into compact structures allows the into compact structures allows the chromatidschromatids to separate without tangling to separate without tangling during cell division.during cell division.

Cell

DNA molecule(double helix comprising

genes)

Individual atoms

Histone proteins

Replicated chromosome

Chromatin: a complex of DNA and protein

Chromosome FeaturesChromosome Features• Chromosomes can be Chromosomes can be

identified by noting:identified by noting:– BandingBanding patterns patterns– Position of the Position of the

centromerecentromere– Presence of Presence of satellitessatellites– LengthLength of the of the

chromatidschromatids

• These features enable These features enable homologous pairs to homologous pairs to be matched and be matched and therefore accurate therefore accurate karyotypeskaryotypes to be to be made.made.

Banding pattern

Satellite endings

Chromosome length

Centromere position

MetacentricSubmetacentric or Subterminal

Acrocentric

Chromosomes Contain GenesChromosomes Contain Genes• A single chromosome may contain A single chromosome may contain

hundredshundreds of genes. of genes.– Below are the Below are the locationslocations of some known of some known

genes on human chromosomes:genes on human chromosomes:

1

ElRh

AMY

Fy

1270Chromosome:

No. of genes:

TYS

4

MN

4659

ABONP

49913

RB

195X

CBDHEMA

773

NucleotidesNucleotides

BaseSugarPhosphate

Adenine

• The building blocks of nucleic acids (DNA and The building blocks of nucleic acids (DNA and RNA) comprise the following components:RNA) comprise the following components:– a a sugarsugar (ribose or deoxyribose) (ribose or deoxyribose)– a a phosphatephosphate groupgroup

• a a basebase (four types for each of DNA and RNA) (four types for each of DNA and RNA)

Structure of NucleotidesStructure of NucleotidesThe chemical structure of nucleotides:The chemical structure of nucleotides:

Symbolic form

Phosphate: Links neighboring sugars

Sugar: One of two types possible: ribose in RNA and deoxyribose in DNA

Base: Four types are possible in DNA: adenine, guanine, cytosine and thymine. RNA has the same except uracil replaces thymine.

Nucleotide BasesNucleotide Bases

PyrimidinesPyrimidinesCytosiCytosinene• • Single-Single-

ringed ringed structuresstructures

ThymiThyminene

• • Always pair Always pair up up with purineswith purines

UracilUracil

Base component

of a nucleotide

• The base The base component of component of nucleotides nucleotides which which comprise the comprise the genetic codegenetic code

PurinesPurinesAdeninAdenin

ee• • Double-Double-ringed ringed structuresstructures

GuaniGuaninene

• • Always Always pair up pair up with with pyrimidinepyrimidiness

DNA StructureDNA Structure

Sugar (deoxyribose)

Phosphate

Purine base

(guanine)

Pyrimidine base

(thymine)

Purine base (adenine)

Pyrimidine base (cytosine)

Hydrogen bonds

• Phosphates link Phosphates link neighboring neighboring nucleotides nucleotides together to together to form one half of form one half of a double-a double-stranded DNA stranded DNA molecule:molecule:

DNA MoleculeDNA MoleculeSpace-filling modelSymbolic representation

Hydrogen bonds

• PurinesPurines join with join with pyrimidinespyrimidines in the DNA in the DNA molecule by way of molecule by way of relatively weak hydrogen relatively weak hydrogen bonds with the bases bonds with the bases forming cross-linkages.forming cross-linkages.

• This leads to the This leads to the formation of a formation of a doubledouble--strandedstranded molecule of molecule of two opposing chains of two opposing chains of nucleotides:nucleotides:– The The symbolicsymbolic diagram diagram

shows DNA as a flat shows DNA as a flat structure.structure.

• The The space-fillingspace-filling model model shows how, in reality, the shows how, in reality, the DNA molecule twists into DNA molecule twists into a spiral structurea spiral structure

DNA Replication 1DNA Replication 1Single-armed chromosomeas found in non-dividing cell

Replication fork

Temporary break

to allow swivel

• DNA is DNA is replicatedreplicated to to produce an produce an exactexact copycopy of a of a chromosome in chromosome in preparation for preparation for cell division.cell division.

• The first step The first step requires that the requires that the coiled DNA is coiled DNA is allowed to allowed to uncoiluncoil by creating a by creating a swivelswivel pointpoint..

DNA Replication 2DNA Replication 2Free nucleotides

are used to constructthe new DNA strand

Parent strand of DNA is used as a template to match nucleotides for

the new strand

The new strand of DNA is constructed

using the parent strand as a template

• NewNew piecespieces of of DNA are formed DNA are formed from free from free nucleotide units nucleotide units joined together by joined together by enzymes.enzymes.

• The free The free nucleotides nucleotides ((yellowyellow) are ) are matched up to matched up to complementary complementary nucleotides in the nucleotides in the original strand.original strand.

DNA Replication 3DNA Replication 3

The double

strands of DNA

coil up into a

helix

Each of the two newly

formed DNA double

helix molecules will

become a chromatid

• The two new The two new strands of DNA strands of DNA coil up into a coil up into a helixhelix..

• Each of the two Each of the two newly formed newly formed DNA strands will DNA strands will go into forming go into forming a a chromatidchromatid

DNA Replication 4DNA Replication 4

A A pairs pairs withwith

TT

TTpairs pairs withwith

AA

GGpairs pairs withwith

CC

CCpairs pairs withwith

GG

Template

strand

Template

strand

Two new

strands forming

• Free nucleotides with their Free nucleotides with their corresponding bases are corresponding bases are matched up against the matched up against the template strand following the template strand following the base pairing rule:base pairing rule:

Control of DNA ReplicationControl of DNA Replication

3'5'

5' 3'Double strand of

original (parental) DNA

Helicase

DNA polymerase III

DNA polymerase I

DNA ligase

Direction of

synthesis

5'

3'

Replicationfork

DNA polymerase III

Leading strand

Swivel point

Ove

rall

dire

ctio

n o

f re

plic

atio

n

Directi

on o

f

synt

hesis

RNA polymerase

• DNA DNA replication replication is is controlled controlled by by enzymes enzymes at key at key stages:stages:

The Leading StrandThe Leading Strand

Ove

rall

dire

ctio

n o

f rep

licat

ion

Directi

on o

f syn

thes

is

5'3'

5'

5

'

3'

Helicase: Splits and unwinds the two-stranded DNA molecule.

1

Swivel point

The leading strand is synthesized continuously in the 5' to 3' direction by DNA polymerase III.

2

DNA polymerase III

The parental strand provides a 'template' for synthesis of the new strand

Replicationfork

• Enzymes can Enzymes can build strandsbuild strandsonly in the only in the 5’5’ to to 3’3’ direction direction

• This means This means that only one that only one strand, called strand, called the the leading leading strandstrand, can , can be be synthesized as synthesized as a continuous a continuous strand.strand.

5'

3'

New complementary strand is

synthesized discontinuously, in

fragments 1000-2000 bp long

5'

Ove

rall

dire

ctio

n o

f rep

licat

ion

RNA primer

Direction of synthesis

RNA polymerase:

Makes a short RNA

primer which is later

removed.

2

DNA polymerase III: Extends RNA primer with short lengths of complementary DNA to make Okazaki fragments.

3Swivel point

Helicase: Splits and unwinds the two-stranded DNA molecule.

3'

1

The Lagging StrandThe Lagging Strand• The other The other

complementary complementary strand, called the strand, called the lagging strandlagging strand, , must be must be constructed in constructed in fragments, which fragments, which are later joined are later joined togethertogether

Enzyme Control of Replication 4Enzyme Control of Replication 4

Direction of

synthesis

The lagging strand is formed in

fragments (called Okazaki fragments)

which are later joined together.3'

Ove

rall

dire

ctio

n o

f rep

licat

ion

3'5'

5'

3'

DNA ligase: Joins

neighboring fragments

together into longer

strands.

5

DNA polymerase I:

Digests the RNA primer

and replaces it with DNA

4

The Cell CycleThe Cell Cycle

Thecell

cycleMitosisM

Second gap as cell

grows and ensures DNA

replication is complete

G2

G1

First gap as cell monitors its

surroundings, growing and

determining whether to replicate

DNA

Synthesis of

DNA to

replicate

chromosomes

S

• The process of mitosis is The process of mitosis is only part of a only part of a continuous continuous cell cyclecell cycle where most of where most of the cell's 'lifetime' is spent the cell's 'lifetime' is spent carrying out its prescribed carrying out its prescribed role; a phase in the cycle role; a phase in the cycle called called interphaseinterphase..

• InterphaseInterphase is itself divided is itself divided up into three stages:up into three stages:– G1G1 First Gap First Gap – SS Synthesis Synthesis– G2G2 Second Gap Second Gap

• Mitosis is the process byMitosis is the process bywhich the cell produceswhich the cell producestwo new daughter cellstwo new daughter cellsfrom the original parent cellfrom the original parent cell

Late Prophase

Chromosomes continue to coil up and appear as double-chromatids

MitosisMitosis

Late Anaphase

Division of the cytoplasm (cytokinesis) is complete.The two daughter cells are now separate cells in their own right.

Cytokinesis

Anaphase

The chromosomes segregate, pulling the chromatids apart

Cell enters

mitosis

Early Prophase

DNA continues condensing into chromosomes and the nuclear membrane begins to dissolve

Metaphase

The mitotic spindle is formed to organize the chromosomes. The spindle consists of fibers made of microtubules and proteins.

Two new nuclei form. The cell plate forms across the midline of the parent cell. This is where the new cell wall will form.

Telophase

Nuclear

Membrane

Interphase

Centrosome, which later forms the spindle, is also replicated.

DNA is replicated to form 2 chromatids

Nucleolus

Mitosis MicrographsMitosis Micrographs

1. Interphase 2. Prophase

4. Anaphase5. Late Anaphase

3. Metaphase

6. Telophase

• Cell division for somatic growth and repairCell division for somatic growth and repair

MeiosisMeiosis

Gametes(eggs or sperm)

1N

2N

Intermediate cell Intermediate cell

1N

First Division(Reduction division)

Second Division('Mitotic' division) 1N

Crossing over may occur at this stage in meiosis

2N

2N

• The purpose of The purpose of meiosis is to meiosis is to produce produce haploid sex haploid sex cellscells..

• Haploid sex Haploid sex cells have only cells have only one copy of one copy of each each homologoushomologous pair of pair of autosomesautosomes plus one plus one sexsex chromosomechromosome

Meiosis IMeiosis I

Anaphase 1

Telophase 1

1N

Intermediate cellIntermediate cell

2N

Metaphase 1 Bivalents line up

on the equator

2N

Prophase 1 Synapsis and

crossing over

2N

Interphase DNA replication

• The The first divisionfirst division of meiosis is called of meiosis is called a ‘a ‘reductionreduction’ ’ division because it division because it reduces (halves) reduces (halves) the number of the number of chromosomes.chromosomes.

• One chromosome One chromosome from each from each homologous pair is homologous pair is donated to each donated to each intermediate cellintermediate cell

Meiosis IIMeiosis II1N

Intermediate cell

NOTE: Half the full

chromosome complement

shown

1N

Prophase 2

Metaphase 2

Anaphase 2

1N

Gamete (egg or sperm) Gamete (egg or sperm)

Telophase 2

• The The secondsecond divisiondivision of meiosis of meiosis is called a ‘is called a ‘mitoticmitotic’ ’ division, because it division, because it is similar to mitosis.is similar to mitosis.

• Sister Sister chomatidschomatids of each of each chromosome are chromosome are pulledpulled apartapart and and are donated to each are donated to each gamete cellgamete cell

Meiosis & Mitosis ComparedMeiosis & Mitosis Compared

Cell division

Cell division

1N 2N

Cell division

Mei

osi

s II

‘Mit

oti

c’ d

ivis

ion

Homologous

chromosomes

pair up at the

equatorial plate

Homologous

chromosomes do not pair

up at the equatorial plate

Mei

osi

s I

Red

uct

ion

div

isio

n

MITOSISMEIOSIS

2N 2N