Asif Jahin

YEAR 11 Biology Notes Module 1

Cell Structure

Inquiry Question 1 : What distinguishes one cell from another?

SYLABUS:

Investigate different cellular structures, including but not limited to:

o Examining a variety of prokaryotic and eukaryotic cells

o Describe the range of technologies that are used to determine a cell’s structure and function

⮚ Prokaryotes

- Unicellular organisms

- No membrane bound nucleus, no mitochondria, no membrane bound organelles

- 2 TYPES: Archaea and Bacteria

⮚ Eukaryotes

- Both Multicellular and Unicellular organisms

- Nucleus and organelles enclosed in membranes

- Some types are : Animal, Plant and Fungi

⮚ Technologies for investigating cell structure and function

A range of technologies have been developed to expand the fields of cell biology and microbiology, allowing a deeper understanding of the prokaryotic and eukaryotic organisms which populate the earth.

⮚ Light Microscopy

- Passing of visible light through a sample with the use of lenses to magnify the image

- Successfully image objects from 0.2 micrometers to 1 millimeter.

- Common staining technique is Gram Staining: colours bacterial cell membranes either pink or purple to help identify cell

Scientific diagram of a light microscope

⮚ Fluorescence microscopy

- Microscopes which can detect fluorescence or phosphorescence, producing images can identify certain aspects of cells.

- USES - Mammalian cells can be stained with fluorescent compounds which bind nucleic acids,

enabling them to identify where the nucleus of the cell is located. - Useful to identify cells which express fluorescent reporter proteins, common technique is

bacterial culturing.

⮚ Electron Microscopy

- Use a beam of electrons to illuminate objects. Electrons have significantly smaller wavelengths than light photons.

- Successfully image objects anywhere from 0.1 nanometers to 1 millimeter.

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- Greater observations of structures within cells, for example organelles are difficult to distinguish under a light microscope.

- Drawback is images must be in a vacuum; cells must be dead to be imaged, not able to view cellular processes in action, cell structure may be slightly different.

- Significantly more expensive than an light microscope

⮚ Cell diagrams

⮚ Eukaryotic Cell diagrams

Animal Cell Plant cell

Plant cell

⮚ Prokaryotic Cell diagram

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Cellular feature and Definition Eukaryotic Prokaryotic

Nucleus: membrane enclosed organelle containing genetic information

Yes, bound to the membrane

No

Nucleic acid storage Multiple chromosomes within the nucleus

Nucleoid and plasmids (circular DNA)

Endoplasmic reticulum: network of membrane-enclosed sacs involved in protein and lipid synthesis

Yes, present in both smooth and rough form

Yes, free flow

Ribosomes: composed of RNA, molecular structure that is the site of protein synthesis.

Yes, found bound to the rough endoplasmic reticulum; larger than prokaryotic type.

Yes, Free-floating in the cytoplasm; smaller than the eukaryotic type

Mitochrondria: organelles responsible for the majority of ATP (energy) production in the cell

Yes No

Cytoskeleton: Structure which give the cell shape, organize cellular parts, and are involved in transport of molecules around cells, and are composed of microtubules, actin filaments and intermediate filaments

Yes No

Lysosomes: cytoplasmic organelle containing enzymes to break down biomolecules, responsible for waster disposal

Yes No

Golgi Apparatus: responsible for packaging Yes No

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proteins for transport around the cell

Chloroplast: organelles contain chlorophyll, responsible for photosynthesis

Yes in plant cells No, photosynthetic prokaryotes have chlorophyll dispersed in cytoplasm

Cell wall: structural layer outside the cell membrane

Yes in plant cells and fungi

Yes

Vacuole: vesicle found in cytoplasm, containing fluids (wastes, water), and providing structural support (turgor)

Yes Yes

Flagella: ‘tail’ present in some cells, responsible for movement.

Yes long and rodlike composed of multiple fibres, microscopic

Yes, composed of one fibre, sub-microscopic

SIZE 10-100 micrometers 0.1 to 5 micrometers

Organelles

Nucleus

▪Membrane-bound: double membrane

▪ Contains DNA

▪ Contains the genetic instructions for cell replication, growth, repair and function

Ribosome

▪Made of proteins and rRNA

▪ No membrane

▪ Synthesises proteins

Endoplasmic reticulum

▪Membrane-bound network of cisternae (membranous sacs)

▪ Ribosomes bind to its membranes, giving it a ‘rough’ appearance

▪ rER Processes and modifies proteins 🡪

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▪ sER Synthesises lipids and steroids, storage🡪

Golgi apparatus

▪Membrane-bound stack of cisternae that are not connected to each other

▪ Processes and packages proteins

Lysosome

▪Membrane-bound vesicle containing digestive enzymes

▪ Digests cellular waste material and foreign matter

Mitochondria

▪Membrane-bound: double membrane, inner membrane is highly folded

▪ Contains DNA

▪ Obtains energy from organic compounds (respiration)

Centriole

▪ Small structure in the cytoplasm, consisting of microtubules

▪ Involved in cell division and the formation of cell structures such as flagella and cilia

Vacuole

▪Membrane-bound, fluid-filled vesicle

▪ Stores substances; also involved in cell structure of plants

Plastid

▪ Small, with double membrane

▪ Contains DNA

▪ Synthesises and stores various organic molecules

Chloroplast

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▪ Spherical or ellipsoidal, with double membrane

▪ Contains DNA

▪ Site of photosynthesis

Cell wall

▪ External structure surrounding cell membrane

▪ Composition depends on type of cell

▪ No membrane

▪ Provides support

▪ Prevents expansion of the cell

▪ Allows water and dissolved substances to pass freely through it

▪ Protection

Cilium or flagellum

▪ External structure consisting of microtubules – hair like structures

▪ Cilia move with an oar-like motion, and are usually shorter and more numerous than flagella

▪ Both structures are involved in the movement of the cell or things around the cell

Nucleoid

▪ The space within a prokaryotic cell where the genetic information, called genophore, is found

▪ Irregularly shaped region

▪ Acts as the nucleus in a bacteria cell however not membrane-bound

Cytoplasm

▪ Gel-like substance composed of mainly water, salts and organic compounds

▪ The fluid that fills the cell

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▪ Breaks down and removes waste material

▪ Aids in movement

▪ Gives cell shape and supports internal structures

Nucleolus

▪ Located in the nucleus (dark staining area of the nucleus)

▪ The site of manufacture of ribosomal RNA and Ribosomes

Cytoskeleton

▪ Consists of microtubules of tubulin (a protein) and filaments of actin (a protein)

▪ Supports the cell structure

▪ Allows for movement

▪ Helps transport organelles and vesicles within the cell

⮚ Cellular Membranes

- Composed of phospholipid bi-layer, - forms a selectively permeable protective layer around cellular contents - controls movement of ions and organic molecules in and out of the cell. - Responsible for cell adhesion, and cell signaling

⮚ Fluid mosaic model

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- Current theory known as fluid mosaic model

- Describes two-dimensional liquid which restricts diffusion across its lipid bilayer.

- Hydrophobic ‘heads’ face outwards. Hydrophilic tail bind together.

- Components include proteins, cholesterol and carbohydrates

- All components perform important functions such as maintain structural integrity, challenging specific molecules across membrane and allowing for cell recognition.

Cell Function Inquiry Function: How do cells coordinate activities within their internal environment

and the external environment?SYLLABUS: Investigate the way in which materials can move into and out of cells, including but not limited to:

- Conducting a practical investigation modelling diffusion and osmosis - Examine the rules of active transport, endocytosis and exocytosis - Relating the exchange of materials across membranes to the surface-area-to-volume ratio,

concentration gradients and characteristics of the materials being exchanged.

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⮚ Diffusion and osmosis (PASSIVE TRANSPORT)

- DIFFUSION - Movement of molecules from an area of high concentration to an area of low concentration

until an equilibrium is reached. DOES NOT REQUIRE ENERGY OUTPUT. - Passive transport - Diffusion can be facilitated – means a mechanism such as ion channel, exists across the

membrane to flow certain molecules through.- OSMOSIS- Subset of diffusion refers to the passive movement water across a membrane to equalize

concentration of a solute on both sides.

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- Are used by cells to regulate their internal conditions, ensuring optimal cell function.- At normal, balanced water levels a cell is in ISOTONIC conditions- Too much water within cell it becomes HYPOTONIC and may lyse due to increased pressure

on the membrane. - Too little water, it is HYPERTONIC and may shrivel due to lack of water

⮚ ACTIVE TRANSPORT

-the movement of molecules across a membrane requiring an input of energy- mostly ATPSide notes

- Occurs in cells when molecules are too large to move across membrane - Or when trying to move across a concentration gradient - Important to move molecules such as glucose and creation of

membrane potentials which drive production of ATP in mitochondria

⮚ ENDOCYTOSIS

- Type of active transport used to bring external materials such as proteins, into the cytoplasm of a cell.

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- Process: engulfs them in part of the outer membrane forming a vesicle inside the cytoplasm

⮚ EXOCYTOSIS

- Opposite of Endocytosis. - Mechanism for cells to actively transport large or charged molecules to the extra-cellular

space- Method to add proteins, lipids, and other molecules to the cell membrane

⮚ FACTORS AFFECTING EXCHANGE OF MATERIALS

⮚ SURFACE-AREA-TO-VOLUME-RATIO

- Ratio between the external membrane surface of a cell and the size of its contents.

- Larger a cell, smaller its surface area to volume ratio because more cytoplasm is being contained in a relative smaller coating of membrane.

- SA:V ratio decrease so does the efficiency of the cell, since the cell contents are less available to the site of exchange

⮚ Concentration Gradients

- The greater a difference in concentration across a membrane, the more rapidly it will diffuse.

⮚ Characteristics of materials

- The physical and chemical properties of a molecule, and how they interact with the cell membrane.

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- The mass of the molecule will affect transport, large molecules will generally be unable to pass through the selectively permeable membrane without the aid of a transporter protein.

- Helps maintain the integrity - The solubility of the molecule will affect transport, - Solubility refers to whether a substance is polar or non-polar - Nonpolar substances move more easily through cell membrane than polar substances

2.5 CELL REQUIREMENTS

SYLLABUS

Investigate cell requirements, including but not limited to

o Suitable forms of energy, including light energy and chemical energy in complex molecules

o Matter, including gasses, simple nutrients and ions o Removal of wastes

All cells require an energy source and a carbon source

⮚ Autotrophs

- Organisms able to produce their own food from their surroundings, using either photosynthesis or chemosynthesis

- Basis of food chain - Produce complex molecules like glucose from inorganic molecules; CO2 and water using

sunlight

⮚ Heterotrophs

- Organisms unable to synthesize their own food, must rely on consumption of other organisms or external carbon molecules for their natural carbon source

- For example Humans consume plants to obtain carbohydrates, protein and other nutrients required for cellular function

2.6 Biochemical processesSYLLABYS

o Investigate the biomechanical processes of photosynthesis, cell respiration and the removal of cellular products and wastes in eukaryotic cells.

METABOLISM: the sum of all chemical processes which take place within an organism.

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⮚ PHOTOSYNTHESIS

Carbon dioxide + Water +Light Glucose + Oxygen 🡪6CO2 +6H2O +Light C🡪 6H12O6 + 6O2

- Process used by autotrophs to produce their own glucose. - Converts light energy into chemical energy and stores this energy in the bonds of glucose

molecules. - Chloroplasts are specialized organelles responsible for performing photosynthesis in plants

and algae. - Obtain Chlorophyll, green pigment excited by certain wavelength of light. This is how light

energy is converted to chemical

⮚ CELL RESPIRATION

▪ Essential biochemical process required for all cells (producing energy)

▪ In terms of biology respiration does not mean to ‘breahe in’

▪ 2 TYPES: AEORBIC and ANAEORBIC

▪ Aerobic means presence of oxygen, Anaerobic meaning without oxygen.

⮚ AEROBIC REPIRATION

Glucose + Oxygen Carbon Dioxide + Water +🡪 Energy

C6H12O6 + 6O2 2CO🡪 2 + 6H2O + ATP energy - Main site

Mitochondria

⮚ Anaerobic Respiration in Human cells

Glucose Lactic acid + Adenosine triphosphate🡪C6H12O6 2C🡪 3H603 + ATP ENERGY

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- When starved from oxygen human cells able to use glucose to produce lactic acid and energy- When you run you can get cramps due to build up of lactic acid affecting your muscle cells

⮚ Anaerobic Respiration or Fermentation in Yeast cells

Glucose Ethanol 🡪 + Carbon dioxide + Adenosine triphosphate

C6H12O6 2C🡪 2H5OH + CO2 + ATP ENERGY

2.7 ENZYMES

Highly specific biological catalysts which increase the rate of metabolic reactions by loosing ‘Activation Energy’

- Enzymes are proteins - Responsible for speeding up/ catalyzing chemical reactions happening in organisms- E.G. breaking down glucose for energy on its own would take years, Enzymes can allow

glucose digestion to happen in a matter of seconds. - Essential in all areas of life without it organisms would blobs of chemicals slowly reacting

over millions of years Activation energy

- Energy needed to begin a reaction between two molecules.

⮚ Chemical Structure of Enzymes

- Made of amino acids bonded in a specific linear order and then folded to form proteins

- Proteins are made of amino acids are joined in a long chain- This chain then folds in on itself to make a specific shape- Each enzyme is specific and will only catalyze one reaction

- Each enzyme has an ‘active site’ where the substrate (reactants) bindACTIVE SITE

- area of the enzyme which contains a specific sequence of amino acids with reactive side chains

The two main theories of how enzymes and substrates interact

⮚ Lock and Key model

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- Describes enzyme as key and the substrate a lock. When the key interacts with the lock, the lock changes shape, but the key remains unchanged for continued use. Analogous represents

- a substrate interacting with an enzyme, forming an enzyme substrate complex and then separating , the substrate changed into products and the enzymes conserved

⮚ Induced fit model

- Elaborates on lock and key model - Enzymes active site is not perfectly shaped to accommodate the

substrate, but changes shape to bind the substrate and act on it

FACTORS EFFECTING ENZYME ACTIVITY

Denaturation: When the shape is significantly altered

⮚ EFFECTS OF PH

- Each enzyme has it own narrow range outside this they will denature 🡪- Most function at neutral/pH 7

⮚ EFFECTS OF TEMPERATURE

- Temp increases 🡪 activity increases, until optimal temp - Above this, enzymes will denature - Heat is altering the chemical bonds within the protein - Optimum temp in humans for enzymes = 37oC

⮚ EFFECTS OF SUBSTRATE CONCENTRATION

- Concentration increases 🡪 rate of reaction increases- Reactions occur until all the active sites on the enzyme are occupied = saturation point

(plateau)

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