Cell Membrane & Homeostasis

Cell Membrane & Cell Membrane & HomeostasisHomeostasis

DEFINITIONS:DEFINITIONS:

DiffusionDiffusion: movement of molecules from : movement of molecules from region of high concentration to low region of high concentration to low concentrationconcentration

Diffusion GradientDiffusion Gradient: the concentration : the concentration spectrum (difference) of solute molecules spectrum (difference) of solute molecules from high concentration to low from high concentration to low concentration.concentration.

Osmosis:Osmosis: diffusion of diffusion of water moleculeswater molecules across a membrane from high water amounts across a membrane from high water amounts (low solute) to low water amounts (high (low solute) to low water amounts (high solute). solute).


Cell membranes are completely Cell membranes are completely permeablepermeable to water. to water. The environment the cell is exposed to The environment the cell is exposed to

can have a dramatic effect on the cell. can have a dramatic effect on the cell. Solute: a dissolved molecule in water. Solute: a dissolved molecule in water.

Eg. Sodium chloride dissolved in water Eg. Sodium chloride dissolved in water

makes a saline makes a saline solutionsolution. The sodium . The sodium chloride is the chloride is the solutesolute. The water is the . The water is the solventsolvent. .


Common cell solutes include salts, sugars, Common cell solutes include salts, sugars, some minerals (iron ions and calcium ions) some minerals (iron ions and calcium ions) and protons (and protons (electrons electrons from acids).from acids).

CONCENTRATIONCONCENTRATION: amount of solute : amount of solute per unit volume of solution. Concentration per unit volume of solution. Concentration can be expressed in mass/volume (g/100ml can be expressed in mass/volume (g/100ml - percentage), ppm (parts per million), - percentage), ppm (parts per million), and moles/volume (molarity). The greater and moles/volume (molarity). The greater the mass or moles per unit volume, the the mass or moles per unit volume, the more concentrated the solution.more concentrated the solution.

3 Osmotic Solution 3 Osmotic Solution TermsTerms

IsotonicIsotonic

Same concentrationSame concentration of solute of solute surrounding a cell as inside the cell. surrounding a cell as inside the cell. When a cell is placed in an isotonic When a cell is placed in an isotonic

solution, the solution, the water diffuses into and out water diffuses into and out of the cellof the cell at the same rate. at the same rate.

The fluid that surrounds the body cells The fluid that surrounds the body cells is said to be “isotonic”.is said to be “isotonic”.

HypertonicHypertonic

The surrounding solutionThe surrounding solution contains a contains a higher concentrationhigher concentration of solute of solute relative to the cell.relative to the cell. When a cell is placed in a hypertonic When a cell is placed in a hypertonic

solution, the solution, the water diffuses out of the water diffuses out of the cellcell attempting to match the solute attempting to match the solute concentration outside of it, causing the concentration outside of it, causing the cell to shrivel. cell to shrivel.

The fluid surrounding the body cell is The fluid surrounding the body cell is said to be “hypertonic”.said to be “hypertonic”.

HypotonicHypotonic The surrounding solution contains a The surrounding solution contains a

lower lower concentration concentration of solute relative of solute relative to the cell (e.g. the cell's cytoplasm). to the cell (e.g. the cell's cytoplasm). When a cell is placed in a hypotonic When a cell is placed in a hypotonic

solution, the solution, the water diffuses into the cellwater diffuses into the cell in in an attempt to dilute the solutes inside the an attempt to dilute the solutes inside the cell, causing the cell to swell and possibly cell, causing the cell to swell and possibly explode in animal cells. explode in animal cells.

Plant cells have a Plant cells have a strong cell wall strong cell wall that that prevents explosions. prevents explosions.

Plant cell central vacuoles will fill to Plant cell central vacuoles will fill to maximum and push against the cell wall – maximum and push against the cell wall – this is called high this is called high turgor pressureturgor pressure..

CELL MEMBRANE CELL MEMBRANE FUNCTION and FUNCTION and

STRUCTURESTRUCTURE The CELL MEMBRANE is chiefly The CELL MEMBRANE is chiefly

responsible for maintaining responsible for maintaining homeostasis inside a living cell using homeostasis inside a living cell using different methods to transport different methods to transport molecules in and out of the cell.molecules in and out of the cell. Too much water can burst the cellToo much water can burst the cell Too many wastes can poison the cellToo many wastes can poison the cell The cell cannot tolerate any great The cell cannot tolerate any great

variations in ion conditions.variations in ion conditions.osmosis animation

Jobs of the cell Jobs of the cell membranemembrane

1.1. Isolate Isolate the cytoplasm from the the cytoplasm from the external environment external environment

2.2. RegulateRegulate the exchange of the exchange of substances (gases and ions)substances (gases and ions)

3.3. CommunicateCommunicate with other cells with other cells

4.4. IdentificationIdentification (proteins and (proteins and carbohydrates on its surface)carbohydrates on its surface)

http://www.goldiesroom.org/AP%20Biology/AP%20Lecture%20Notes%20pdf/LN014--Ch05--Cell%20Transport.pdf


DESCRIPTIONDESCRIPTION The The fluid mosaic modelfluid mosaic model (S.J Singer) (S.J Singer)

selectively-permeableselectively-permeable: allows some : allows some substances in all the time, some only substances in all the time, some only when needed, excludes others, allows when needed, excludes others, allows one-way flow of some.one-way flow of some.

Fluid portion is a double layer of Fluid portion is a double layer of phospholipids, called the phospholipids, called the phospholipid phospholipid bilayer.bilayer.

large transport proteinslarge transport proteins, oligoproteins , oligoproteins and oligosaccharides aid in transportand oligosaccharides aid in transport energy is required from the cellenergy is required from the cell aid in communication as well as identificationaid in communication as well as identification

Phospholipid bilayerPhospholipid bilayer Phospholipids contain a Phospholipids contain a hydrophilic headhydrophilic head

and a non-polar and a non-polar hydrophobichydrophobic tail tail Hydrogen bonds form between the Hydrogen bonds form between the

phospholipid phospholipid “bilayer”“bilayer” and the watery and the watery environment inside and outside of the cell.environment inside and outside of the cell.

Hydrophobic (water fearing) interactions Hydrophobic (water fearing) interactions force the “tails" to face inward.force the “tails" to face inward.

Phospholipids are not bonded to each Phospholipids are not bonded to each other, which makes the double layer other, which makes the double layer fluidfluid..

Cholesterol embedded in the membrane Cholesterol embedded in the membrane makes it stronger and less fluid.makes it stronger and less fluid.


The different The different componentscomponents of a of a plasma membrane are plasma membrane are integral integral proteinsproteins, , peripheral proteins, , glycoproteins, , phospholipids, , glycolipids, and in some cases , and in some cases cholesterol, and , and lipoproteins.

Construction of the Cell Membrane - Learning Activity

detailed cell membrane animation

Proteins Embedded in Proteins Embedded in Membrane Serve Different Membrane Serve Different

FunctionsFunctions Transport ProteinsTransport Proteins

regulate movement of substanceregulate movement of substance

Channel ProteinsChannel Proteins form small openings for molecules to form small openings for molecules to

diffuse through like waterdiffuse through like water

Carrier ProteinsCarrier Proteins binding site on protein surface "grabs" binding site on protein surface "grabs"

certain molecules and pulls them into certain molecules and pulls them into the cell the cell animation

Gated ChannelsGated Channels similar to carrier proteins, not similar to carrier proteins, not

always "open"—eg. Bind and pull in always "open"—eg. Bind and pull in calcium calcium ions when needed. This ions when needed. This requires cell energy—active requires cell energy—active transport.transport.

Receptor ProteinsReceptor Proteins molecular triggers that set off cell molecular triggers that set off cell

responses (such as release of hormones responses (such as release of hormones or opening of channel proteins)or opening of channel proteins)

e.g. The junction e.g. The junction between nerve between nerve cells requires the cells requires the transmission of transmission of neurotransmitterneurotransmitters between s between synaptic gaps—synaptic gaps—these chemicals these chemicals bind onto bind onto receptor receptor proteins.proteins.

Recognition ProteinsRecognition Proteins - ID tags, to - ID tags, to identify cells to the body's immune identify cells to the body's immune system (called system (called antigensantigens))

TRANSPORT TRANSPORT MECHANISMSMECHANISMS

1.1. PASSIVE TRANSPORTPASSIVE TRANSPORT

2.2. ACTIVE TRANSPORTACTIVE TRANSPORT1.1. ENDOCYTOSISENDOCYTOSIS

2.2. EXOCYTOSISEXOCYTOSIS

Types of Cellular Types of Cellular TransportTransport Passive TransportPassive Transport

cell doesn’t use cell doesn’t use energyenergy1.1. DiffusionDiffusion2.2. Facilitated DiffusionFacilitated Diffusion3.3. OsmosisOsmosis

Active TransportActive Transportcell does use energycell does use energy1.1. Protein PumpsProtein Pumps2.2. EndocytosisEndocytosis3.3. ExocytosisExocytosis

high

low

Weeee!!!

high

low

This is gonna

be hard

work!!

•Animations of Active & Passive Transport

1. Passive Transport 1. Passive Transport (p. 198)(p. 198)

Simple DiffusionSimple Diffusion - water, oxygen and - water, oxygen and other molecules move from areas of other molecules move from areas of high concentration to areas of low high concentration to areas of low concentration, concentration, down adown a concentration concentration gradient.gradient.

Note – Note – OsmosisOsmosis is the diffusion of water is the diffusion of water

DDiffusion animationPassive Transport Animation

1. Passive Transport 1. Passive Transport (cont’d)(cont’d)

Facilitation Diffusion - Facilitation Diffusion - diffusion diffusion that is that is enabled by proteinsenabled by proteins (channel or carrier proteins) which (channel or carrier proteins) which bind onto required molecules so that bind onto required molecules so that they flow into the cell.they flow into the cell.

Animation: How Facilitated Diffusion Works

Contractiles Vacuoles are found in Contractiles Vacuoles are found in freshwater microorganisms - they freshwater microorganisms - they pump out excess water.pump out excess water.

Recall:Recall: Turgor pressure occurs in plants Turgor pressure occurs in plants

cells as their central water vacuoles cells as their central water vacuoles fill with water. fill with water.

Factors Affecting Rate of Factors Affecting Rate of DiffusionDiffusion

1. Size1. Size

small molecules can slip through small molecules can slip through phospholipids bilayer easier than phospholipids bilayer easier than large moleculeslarge molecules

very large molecules may not be very large molecules may not be able to diffuse at all able to diffuse at all

2. Concentration2. Concentration

the greater the concentration the greater the concentration gradient (bigger range) the quicker gradient (bigger range) the quicker a material diffuses (makes the a material diffuses (makes the molecules want to move faster) – molecules want to move faster) – think of a crowded roomthink of a crowded room

3. Temperature3. Temperature

In general as temperature increases In general as temperature increases – molecules move faster which – molecules move faster which translates into faster diffusiontranslates into faster diffusion

4. Polarity of molecules4. Polarity of molecules

Water-soluble (polar) molecules will Water-soluble (polar) molecules will not easily move through the not easily move through the membrane because they are stopped membrane because they are stopped by the middle water-insoluble by the middle water-insoluble (nonpolar) layer(nonpolar) layer

5. Surface Area5. Surface Area As a cell’s size increases its volume increases As a cell’s size increases its volume increases

much quicker than it’s surface area.much quicker than it’s surface area. If you double individual lengths (1 cm to 2 cm) the If you double individual lengths (1 cm to 2 cm) the

surface areas increases 4 times, and the volume surface areas increases 4 times, and the volume increases 8 times.increases 8 times.

If cell size is doubled, it would require 8 times If cell size is doubled, it would require 8 times more nutrients and have 8 times s much waste. more nutrients and have 8 times s much waste. SA only increases by a factor of 4 – not enough SA only increases by a factor of 4 – not enough surface area through which nutrients and wastes surface area through which nutrients and wastes could move. could move. Cell would either starve or be poisoned (waste Cell would either starve or be poisoned (waste

products)products) Cells divide before they come too large to Cells divide before they come too large to

function. function.

2. Active Transport 2. Active Transport (p. 199)(p. 199)

Involves moving molecules "uphill" Involves moving molecules "uphill" againstagainst the concentration gradient, the concentration gradient, which requires energy. which requires energy. Uses Uses carriercarrier protein molecules as protein molecules as

receptors.receptors. One may transport calcium ions another One may transport calcium ions another

glucose molecules. glucose molecules. There are hundreds of these types of There are hundreds of these types of

protein molecules.protein molecules.

*Each one changes shape to accommodate a *Each one changes shape to accommodate a specific molecule. specific molecule.

2. Active Transport2. Active Transport (cont’d) (cont’d)

Their activity can be stopped from Their activity can be stopped from transporting molecules with transporting molecules with inhibitorsinhibitors (unfortunately, these are (unfortunately, these are usually poisons) which:usually poisons) which: either destroy the membrane proteineither destroy the membrane protein or just plug it up or just plug it up (e.g. for your neurons – tetanus & (e.g. for your neurons – tetanus &

botulinum-B secrete a poison that botulinum-B secrete a poison that

suppress the Na/K pump)suppress the Na/K pump)

active transport animationhttp://www.biology4kids.com/files/cell2_activetran.html

Sodium-Potassium PumpSodium-Potassium Pump Pumps out 3 sodium atoms for ever 2 Pumps out 3 sodium atoms for ever 2

potassium atoms taken in against potassium atoms taken in against gradient in gradient in the cell.the cell.

ATP and the Na/K PumpATP and the Na/K Pump

Animation: How the Sodium Potassium Pump WorksAnimation: How the Sodium Potassium Pump Works

The H+/K+ ATPaseThe H+/K+ ATPase The parietal cells of your stomach (lining) The parietal cells of your stomach (lining)

use this pump to secrete use this pump to secrete gastricgastric juice. juice. These cells transport These cells transport hydrogen ionshydrogen ions (H (H++) )

from a concentration of about 4 x 10from a concentration of about 4 x 10-8-8 M M within the cell to a concentration of about within the cell to a concentration of about 0.15 M in the gastric juice (giving it a 0.15 M in the gastric juice (giving it a pHpH close to close to 22). ). Recall: pH – power of the HRecall: pH – power of the H++ ion ion

Small wonder that parietal cells are Small wonder that parietal cells are stuffed with mitochondria and use huge stuffed with mitochondria and use huge amounts of amounts of energyenergy as they carry out this as they carry out this three-million fold concentration of protons. three-million fold concentration of protons.

The H+/K+ ATPaseThe H+/K+ ATPase

Ca2+ ATPasesCa2+ ATPases In resting In resting skeletalskeletal muscle, there is a much muscle, there is a much

higher concentration of calcium ions (Ca2+) higher concentration of calcium ions (Ca2+) in the sarcoplasmic reticulum (__) than in the in the sarcoplasmic reticulum (__) than in the cytosol (_________).cytosol (_________).

Activation of the _______ fiber allows some of Activation of the _______ fiber allows some of this Cathis Ca2+2+ to pass by to pass by fascilitatedfascilitated diffusion into diffusion into the cytosol where it triggers contraction. the cytosol where it triggers contraction. After contraction, this CaAfter contraction, this Ca2+2+ is pumped back is pumped back into the sarcoplasmic reticulum. This is done into the sarcoplasmic reticulum. This is done by a Caby a Ca2+2+ ATPase that uses the energy from ATPase that uses the energy from each molecule of each molecule of ATPATP to pump 2 Ca to pump 2 Ca2+2+ ions. ions.

ExocytosisExocytosis MovesMoves large, complex molecules large, complex molecules

such as proteins out of the cell such as proteins out of the cell membrane.membrane.

Large molecules, food, or fluid Large molecules, food, or fluid droplets are packaged in membrane-droplets are packaged in membrane-bound sacs called bound sacs called vesicles.vesicles.

EndocytosisEndocytosis EndocytosisEndocytosis moves large particles moves large particles

(huge molecules or molecular (huge molecules or molecular conglomerates) into a cell.conglomerates) into a cell.

endo & exocystosis animationsendo & exocystosis animations

PhagocytosisPhagocytosis Phagocytosis Phagocytosis is another type of is another type of endocytosisendocytosis

used for massive transport.used for massive transport.Cell membrane extends out forming Cell membrane extends out forming pseudopods pseudopods (fingerlike projections) that (fingerlike projections) that surround the particle.surround the particle.

Membrane pouch encloses the material & Membrane pouch encloses the material & pinches off inside the cell making a pinches off inside the cell making a vesicle.vesicle.

Vesicle can fuse with Vesicle can fuse with lysosomeslysosomes(digestive (digestive organelles) or release their contents in the organelles) or release their contents in the cytoplasmcytoplasm

Animation: PhagocytosisAnimation: Phagocytosis HowStuffWorks "Phagocytosis"HowStuffWorks "Phagocytosis"

Used byUsed by ameba ameba to feed & to feed & white white bloodblood cells cells to kill bacteria. to kill bacteria.Known as Known as “killer cells"“killer cells"

Pinocytosis Pinocytosis is another type of is another type of endocytosisendocytosis

Cell membrane surrounds fluid dropletsCell membrane surrounds fluid droplets Fluids taken into membrane-bound vesicleFluids taken into membrane-bound vesicle Known as Known as ““cell drinking”cell drinking”

•Exocytosis is used to remove large products from the cell such as wastes, mucus, & cell products such as hormones and antibodies.

•Exocytosis is the process used by our memory cells (white blood cells that produce antibodies to fight infection).

•It is also used by our gland cells to secrete hormones when needed.

phagocytosisphagocytosis

animationanimation

In SummaryIn Summary

Essential Biochemistry - Membrane TransportEssential Biochemistry - Membrane Transport

Transport FlowchartTransport FlowchartTransport of Materials

Across a Membrane

Active

Phagocytosis

Pinocytosis

Ion Pum

p

Facilitated

Diffusion

OsmosisSimple

Diffusion

Passive

Endocytosis

Exocytosis

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Cell Membrane & Homeostasis