Session 1/2 Flashcards
(27 cards)
General function of Biological membranes
1) Continuous, highly selective permeability barrier
2) Control of the enclosed chemical environment
3) Communication
4) Recognition- signalling molecules
- Adhesion proteins
- Immune surveillance
5) Signal generation in response to stimuli (electrical, chemical)
Membrane composition?
40% lipid
60% protein
1-10% carbohydrate
20% of total weight is water
What types of lipid membranes are there?
Phospholipid
Glycolipids
Cholesterol
In Phospoholipids what is it composed of?
- Polar head groups: Choline, serine, inositol, ethanolamine
- Fatty acid chain
What is the similarity of glycolipids and phospholipids?
They both have fatty acid chains (Hydrophobic) and a hydrophilic head group
In the lipid bilayer, how does the structure end up that way?
- Water makes H-bonds with head groups to stabilise membrane structure
- It needs water to drive tails together in order to stabilise head groups.
- This increases entropy
How does a lipid micelle structure occur?
Hydrophobic groups are together.
Water molecules are minimised
Entropy is increased
What does ampiphatic mean?
Head group is hydrophilic
Fatty acid chain is hydrophobic
What is meant by a fluid membrane?
Proteins can move around within the membrane
What does the kink in the fatty acid chain do?
The kink is caused by a cis double bond and it increases fluidity by decreasing the phospholipid packaging at a lower temp
What is meant by the fluid mosaic model?
Structure of the plasma membrane as a mosaic of components with the phospholipid bilayer, cholesterol (sterols),proteins and carbohydrates that the membrane a fluid character.
What types of proteins are there in the fluid mosaic model?
Peripheral proteins
Peripheral lipid linked proteins
Integral protein that goes through the protein with a hydrophobic helix (mainly due to hydrophobic amino acid residues) and outer hydrophilic part
What is the paradoxical effects of cholesterol on the fluid mosaic model?
At lower temperatures:
Cholesterol horizontally reduces the phospholipid packaging between adjacent molecules and hence increases the fluidity
At increasing temps:
4 sterol rings reduces the phospholipid chain’s fatty acid motion, it extends membrane stability over the range of temp, reducing excess fluidity
What are the proteins varying degrees of mobility within the membrane bilayer and what are they dependant on?
Conformational change- Receptor binding its ligand. Agonist causes a conformational change to signal inside of the cell
Flexion-Tails ‘wobble’ about the C-C single bonds
Rotation- Rotary motion around it’s position
Lateral diffusion- Vibration+ rotation
Flip-flop rotation- Where lipids flip between layers
Depend on Temp+ Molecular mass
Greater mass, higher melting point
What primary physiological factors govern whether saturated membrane lipids exists in a gel or fluid state?
Chain length- longer fatty acid chains decreases the fluidity
What are lipid rafts? What are the types?
Cholesterol complexes with glycosphingolipids.
- Makes the membrane less fluid.
- Scaffolding: proteins involved in signal transduction- makes transfer of info more efficient.
- Partitioning: changes their micro-environment, new interacting
- Raft clustering: amplify signalling by bringing signalling components together
Hydration in maintenance of physiological membrane structure and function?
Bilayer head groups facing towards surrounding water and the tails inwards. Without water the cell membranes would lack structure and cells would be unable to keep important molecules inside the cell and harmful outside the cell
Why are flip-flop movements rare?
Protein’s can’t flip-flop as they can’t overcome energy barrier due to extensive hydrophillic regions.
Describe the composition of the erythrocyte skeleton and specify which are adapter proteins and which are integral membrane proteins
Spectrum and actin are anchored to the erythrocyte membrane via adaptor proteins called ankyrin and band 4.1 to integral membrane proteins called band 3 and glycophorin A.
How are cytosilic and membrane proteins directed to the ER membrane? What enables insertion of the membrane protein?
Cytosilic and membrane proteins are synthesised by ribosomes. When the SRP recognises the leading sequence at the N terminal end, it halts protein synthesis on the ribosome. The SRP recognised by the signal sequence receptor on the ER membrane, which is part of the protein trans locator complex.
How does water permeate a lipid bilayer?
Water moves via diffusion and osmosis despite the hydrophilic domain as it is small and uncharged.
Aquaporin channels are not ion channels but permit the rapid water diffusion above the rate of passive diffusion through the lipid bilayer.
Aquaporin has a hydrophillic pore.
Has positively charged residues in pore in order to main H+ ion gradients.
What types of molecules can permeate a lipid bilayer?
Hydrophobic molecules- Oxygen, Carbon dioxide, nitrogen
Small uncharged polar molecules- Water, urea, flyer of.
What are the free ion distributions across the cell membrane?
Sodium ions- 145mM outside, 12Mm inside
Chloride ions- 123mM outside, 4.2mM inside
Calcium ions- 1.5mM outside, times 10 to the minus number 7 inside
Potassium ions- 140mM outside, 4mM inside
What are the roles of transport processes?
- Maintenance of ionic composition
- Maintenance of intracellular pH
- Regulation of cell volume
- Concentration of metabolic fuels and building blocks
- The extrusion of waste products of metabolism+ toxic substances
- The generation of ion gradients necessary for the electrical excitability of nerve and muscle
