Session 1 - Lipids, Proteins + Membrane Structure Flashcards
What is the composition of the dry weight of the membrane?
- 40% Lipid
- 60% protein
- 1-10% Carbohydrate
Describe the structure of a phospholipid molecule
Head group - range of polar molecules (aa’s, choline so, amines and sugars)
Fatty acid “tail” - Lots of variety (C16+18 most common), unsaturated, cis double bond creates a kink in chain
What are Glycolipids?
Sugar containing lipids
What is Sphingomyelin?
Only phospholipid not based on glycerol (when in membrane is very similar to others)
What are Cerebrosides?
Glycolipid with sugar monomers as head groups
What are Plasmalogens?
Non-classical Phospholipids
What are Gangliosides?
Glycolipids with sugar oligosaccharides for head groups
What does the distribution of lipids in the mebrane depend on?
Tissue type and function
What two structures do Amphipathic molecules readily form in water?
Micelles and Bilayers
What forces and between what regions drive Bilayer formation?
Vdws between the hydrophobic fatty acid chains
Name the four ways that lipids can move in a membrane?
- intra-chain motion
- Axial rotation
- Lateral diffusion along same plane
- Flip-Flop
Name the ways membrane proteins can move?
- Lateral movement
- Rotation
- Conformational change
What restricts membrane protein movements?
- Cholesterol levels in particular region
- Associations with other membrane proteins
- Association with extra-membranous proteins (e.g cytoskeleton)
How do Peripheral proteins bind to the membrane and how can they be removed?
- Electrostatic forces and H-bonds
- pH changes or Ionic strength changes
How are integral membrane proteins bound to the membrane and how can they be removed?
- Interact with hydrophobic region of bilayer
- Agents that compete for hydrophobic interactions (e.g detergents, organic solvents)
How is membrane protein synthesis different to secretory protein synthesis?
The protein has to span the membrane not sit solely within it
How does a membrane protein achieve its spanning of the membrane in its synthesis?
Through the addition of a stop transfer signal which is a highly hydrophobic chain of around 20 aa’s
What are Hydropathy plots used for?
To see how many transmembrane regions a protein has
Why is membrane asymmetry important?
Important for biological function
I.e Ensure receptors are situated on the same side of the membrane that their substrate will be
Why is the “kink” in the FA chain important?
It decreases phospholipid packing and hence increases fluidity of the membrane
How does cholesterol increase packing in the membrane?
Forms H-bonds with FA chain
How does cholesterol decrease membrane fluidity?
Decreases the packing by being a physical barrier between chains
What is protein lateral diffusion affected by?
- Size
- Aggregation
- Association with other proteins (intra or extracellular)
- Amount of cholesterol in near vicinity
What is the erythrocyte cytoskeleton composed of and why is it important?
Spectrin and Actin
Maintains shape of RBCs
How does the cytoskeleton attach to the membrane?
Ankyrin and Glycophorin
Bound to
Band 3 and Band 4.1 respectively
What are Haemolytic anaemias in general?
RBCs become spherical and are therefore subject to increased lysis due to shearing forces of capillary beds
What is Hereditary Spherocytosis?
Spectrin levels depleted, RBCs round up, leads to increased lysis
Bone marrow cannot compensate and hence a haemolytic anaemia results
What are Amphipathic molecules?
Molecules with both Hydrophobic and Hydrophilic moieties
What is Hereditary Elliptocyosis?
Spectrin molecules are unable to form heterotetramers, RBCs form elliploid shape (rugby ball) and a Haemolytic anaemia results
