ICPP Flashcards
What does amphipathic mean for lipid membranes?
One part of the lipid membrane is hydrophilic and one part is hydrophobic:
- The phospholipid head interacts with water.
- The fatty acid tails avoid water.
What drives the structure of the lipid membrane?
Energetic stability - it is the conformation that requires the least energy to maintain.
Which conformation of phospholipids have a kink in the fatty acid tail?
Unsaturated, cis conformations.
What are the main parts of a phospholipid and what are the different types of the hydrophilic part?
There is a phosphate and polar head group, a glycerol backbone and 2 fatty acid chains. The polar head group can be:
- Amines.
- Amino acids.
- Choline.
- Inositol.
What is the difference between sphinogmyelin and a normal phospholipid?
It has no glycerol backbone, and instead contains a sphingosine molecule instead.
There are no ‘kinks’ as they are all trans isomers.
The fatty acid tails are often unequal lengths.
What is the structure of a cerebroside? Where are they usually found?
Contains a sphingosine group, a fatty acid tail and a monosaccharide (usually glucose or galactose) polar head group.
They are usually found in the myelin sheath of axons in the CNS and PNS.
What is the structure of a ganglioside and where are they found?
A sphingosine, a fatty acid tail and an oligosaccharide chain.
They are found extending out from cell surfaces, and important to the CNS.
What are the roles of cerebrosides?
Stabilising membranes.
Cell-to-cell recognition.
Immune system.
What are the roles of gangliosides?
Immune system.
Cell-to-cell signalling and CNS development.
Lipid rafts.
What are the structural characteristics of cholesterol?
Hydrophilic -OH head group.
Hydrophobic planar steroid ring with a small fatty acid tail.
What are the functions of cholesterol in membranes?
Compose about 30-40% of membrane lipids.
They enhance temperature range for membrane fluidity AND stability.
Lipid raft formation.
What is the trade off between fluidity and stability?
Too stable will restrict movement of proteins and inhibits permeability.
Too fluid will lose the organisation.
What are the main factors affecting membrane fluidity?
Temperature - the greater temperature, the greater the fluidity.
Molecular mass - the greater the molecular mass, the less able to move it is.
How does the fluid behaviour change between saturated and unsaturated lipids and why does this occur?
In the body, at 37 degrees Celsius, saturated phospholipids are solid as the melting point is between 45 and 75 degrees, compared to -6 of unsaturated, making them fluid-like.
What causes the increased fluidity of unsaturated phospholipid molecules?
The C to C double bond’s cis conformation creates a kink which makes the phospholipids harder to pack in together, increasing the space between phospholipids, disrupting the lattice structure.
How does cholesterol exerts its effects on the lipid membrane?
The hydroxyl polar head group interacts with polar head groups of other phospholipids, inhibiting movement.
The rigid steroid plates inhibit movement of fatty acid tails, increasing stability.
The angle of the steroid plates interferes with the crystalline packing, increasing fluidity.
PREVENTS ABRUPT CHANGES TO MEMBRANE FLUIDITY ACROSS TEMPERATURE RANGES.
What is a lipid raft, and what is its function?
It is a specialised distribution of lipids around 100nm long, with more cholesterol, sphingomyelin and glycolipids.
It is more structured to provide a stable environment for signalling proteins and for the holding of receptors and signalling molecules.
What is the relevance of the fluid mosaic model for the whole body function?
Fluidity and flexibility is required for protein function.
Cell membranes are required for the transmission of forces throughout cells and tissues.
What are the 2 types of peripheral proteins?
External membrane face (outside the cell).
Internal membrane face (inside the cell).
What is the role of the cytoskeleton and peripheral protein interactions?
Provides flexibility and elasticity to the cell membrane.
Disperses forces across the cell, preventing mechanical disruption.
What are lipid anchored proteins?
The are proteins included in the integral protein category due to the covalent bond formation between the protein outside the cell and the fatty acids inside the cell.
They can move laterally.
What are different protein interactions that can occur and their functions?
Aggregation - signalling.
Tethering externally - connect to the ECM for transmission of forces.
Tethering internally - connect to cytoskeleton for strength and flexibility.
Cell-to-cell interactions - cadherins that form tissues, transmit forces, and have a signalling role.
What is the function of Band 3 on RBCs?
HCO3-/ Cl- antiporter to transport CO2.
What does glycophorin do in RBCs?
Reduces friction forces.
What does ankyrin do in RBCs?
Anchors Band 3 to spectrin.
What keeps the cytoskeleton proteins of RBCs in place?
The polar/ ionic bonds.
How does cytochalasin disrupt the cytoskeleton formation?
Inhibits actin polymerisation, preventing the anchoring of spectrin and glycophorin occurring.
What type of molecules can pass straight through a lipid membrane? Give an example.
Hydrophobic molecules, like benzene.
Small uncharged polar molecules, like water.
What does Fick’s law state?
The rate of passive diffusion through a membrane depends on the permeability of the membrane and concentration gradient of the molecule.
What are the two mechanisms of bulk water flow and what are the characteristics of them?
Passive diffusion:
- Occurs across the entire surface of the cell membrane.
- It is bi-directional.
- Water crosses until the solute equilibrium is reached.
Facilitated diffusion - aquaporins:
- Integral membrane proteins.
- It is bi-directional.
- Equilibrium is reached rapidly.
What makes non-gated pores good at facilitating the ability to reach equilibrium quickly?
They are always open.
How do gated pores facilitate diffusion?
The molecule enters the pore, causing a conformational change, allowing the molecules to be released - it is ping-pong transport.
Outline the sequence of how carriers allow the movement of molecules into cells.
The carrier is open to molecules outside the cell.
The molecule enters the carrier, closing the cell to the outside.
The carrier undergoes a further conformational change, opening the carrier to the inside of the cell.
The molecule can then flow into the cell, and the carrier then closes off to the inside of the cell.
What are some characteristics of carrier proteins?
They allow facilitated diffusion to occur.
It involves binding and conformational changes to occur.
A limited number of substances can be moved.
The central pore is usually aqueous.
What are the two types of carrier proteins?
Uniporters - they transport one molecule at a time down the concentration gradient.
Co-transporters - these can be symporters that allow two or more substances to flow in the same direction, or antiporters that transport two or more substances in opposite directions.