AS Level Biology - 4) Membranes
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Transcript of AS Level Biology - 4) Membranes
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