4. MembranesAnd Transport

The Structure of the Cell Membrane

PhospholipidCholesterolProtein – Transport, ChannelGlycoproteinGlycocalyx

Semi-permeability

Small, nonpolar molecules can pass through membranes – passive diffusion

Gases[O2, CO2, Ethanol, lipid, H2O can move through slowly, large non-polar can still pass through slowly]

Charge molecules (Sodium etc. Can not pass through)

Large, polar molecules can not pass through

phospholipid

Amphipathic – Has Fatty Acid tails which are hydrophobic – 2 phospholipid’s tail sections turn toward each other

The Phosphate heads turn to aqueous

A bilayer is formed

Cholesterol

Very stable structure due to a lot of rings

A bufferTemperature decrease – it

increases the fluidityTemperature increase –

reduce the fluidity

Proteins Intrinsic, Extrinsic,

Transmembrance, Lipid BoundFunctions:1. Cell recognition 2. Intercellular joining3. Transport4. Enzymes5. Signaling

Transport ProteinChannel Protein – Does not require energy –

goes with the concentration gradient – when the cell requires certain ions or substance (eg. porin)

Carrier protein – take substances from outside and pump it inside, or vice versa – go against concentration gradient – use energy – ATPase to break down ATP

The Glycoprotein, Glycolipid and

GlycocalyxThe carbohydrate chain sticking out forms

hydrogen bond which help stabilizes the cell membrane

Sugary coating – Glycocalyx on the membrane

The carbohydrate differentiates the proteins/ lipids allowing them to act as receptors

Receptor molecules

Signaling Receptors – recognize messages from hormones or neurotransmitter eg. Glucagon receptor in liver cell

Endocytosis receptor – bind to molecules that are going to be engulfed by a cell

Cell adhesion – binds cell to cellAct as cell markers for recognition –

carbohydrate portions can determine the blood type

Cell Signaling

Important to how an organism coordinates Stimulus to Receptor to target to response Transduction is the conversion of the original

message for transmission

Uses both electrical and chemical agents Signaling molecules ten to be small – easy for

transport Steroid hormones are non-polar, can diffuse through

and bind to receptors in cytoplasm or uses

Signaling Cascade In case of water soluble The signal will be specific to certain the cell itself Changes the shape of the receptor – allowing it to interact with the next

component Affects the G protein – activating the enzymes to send out the second

message (G protein gets its name from how it uses GTP [Guanine Triphosphate

instead of ATP]) Many small soluble signaling molecules released (amplifying the message) These molecules activate enzymes which in turn activate more enzymes to

conduct to the orders (release enzymes, secretes, move, transcribe, divide) This whole process started by the G-protein is called the Signaling Cascade

Passive Transport

Diffusion: The movement of fluid molecules from an area of high concentration to an area of low concentration down a concentration gradient, across a permeable membrane.

Osmosis: The diffusion of water across a selectivly permeable membrane from an area of low solute concentration (high water potential) to an area of high solute concentration (low water potential) down the water potential gradient

Facilitated Diffusion

Diffusion

Factors affecting Diffusion1. The Surface Area – more surface area

encourages diffusion eg. Mitochondria, Microvilli

2. Steepness of the gradient3. Surface Area4. The nature of the molecules

Facilitated Diffusion

Passive transports aided by proteins For large, polar substances – Sodium, Chloride, Glucose They move down the concentration gradient through a

certain protein Channel protein – water-filled pores Carrier proteins – secondary active transport? Usually facilitated diffusion depends not only on the

normal factors but also the presence of these protein and whether or not they are open.

Osmosis/ Water Potential

Water Potential: Tendency of water to move: The concentration of solute and the pressure applied

Pressure can increase water potentialWater potential of pure water is 0, so any the

rest will be negative because they don’t get higher than this

Study pages 83 – 85 thoroughly – this can be incredibly confusing

Salute Potential

The extent of which the concentration of the solutes affect the water potential

At pure water – 0, so gets more and more negative as solute increases

BE SURE TO READ UP ON THIS PART

Active Transport

Active Transport of ions eg. Sodium Potassium Pump

Bulk transport1. Endocytosis (Phagocytosis – cell eating,

Pinocytosis – cell drinking)2. Exocytosis

Sodium Potassium pump

When ions needed to be transport against its concentration gradient

Make use of carrier proteinsPump 3 sodium out, allowing 2 potassium inThe pump has a receptor site for ATPATPase to break down to ADP