Lecture 19 Flashcards
What does cholesterol do to membranes?
Cholesterol will make the membrane more fluid in ordered membranes (cold conditions) and makes it more rigid if the membrane is fluid (hot).
Where can lipids within the membrane move to? What else is found in the membrane?
Membrane lipids will migrate rapidly in their plane of the membrane but swapping planes is very rare. Proteins also move around the membrane and make up a large proportion of the membrane.
what are membrane proteins used for and what can they be relative to the membrane?
Membrane proteins are used for cell-cell contact, surface recognition, cytoskeleton contact, enzymes, transporters and as receptors and signaling. They can be integral (part of the membrane) or peripheral (on the edge of the membrane, not part of it).
How are proteins attached to the membrane?
The peripherals are generally held in place by non covalent electrostatic interactions (positive and negative interactions). The integral proteins are attached via groupings of non polar amino acids in the protein amino acid sequence, these will attempt to maintain their position with the hydroophobic tails. Polar amino acids are kept outside and the seperation of these polar parts of the protein via the membrane further strengthens the position.It can also be attached by anchoring domains, part of the protein going in (but not through) the membrane, this anchoring part will be non polar. Attachment can also be done via post-translational addition of a lipid via a side chain of the lipid to the protein, acting as an anchor.
What is the general trend of membrane composition? Give an example
The outside of the membrane has more sugars than the inside, this is because proteins are often modified by glycolysation, they also have other composition differences.
How are non polar molecules transported across the membrane? Compare with polar. What does the non polar molecule transport rely on?
Non polar molecules don’t need a transporter to get across the membrane, polar molecules do. The transport of non-polar molecules is dependent on the hydrophobicity (how non polar it is) and concentration of the molecules. The general trend is that the more hydrophobic and higher concentration gradient the molecule the more permeable it is.
How do polar molecules get through the membrane?
Polar molecules get through the membrane via polar holes made by proteins in the membrane, these can be channels or transporters.
Channels: These can be open or closed spontaneously or due to stimulus, when open it is open to both the intracellular and extracellular space, this will allow polar molecules through via diffusion.
transporters: These are open to either the intracellular or extracellular space, the binding of molecules induces a conformational change, this changes the open side these are much slower at transporting than channels (unless the molecule has a low concentration and the transporter pumps against the gradient).
What terms refer to what transport processes can typically be?
Transport processes can be: non mediated (no protein needed), mediated (uses a protein), passive (movement down a concentration gradient, needs no energy), active (requires energy input to move a molecule up its concentration gradient, this may come from hydrolysis of ATP or via co transport of another molecule down its concentration gradient) and co transport is the movement of two molecules by a transporter (can be symport, both in the same direction or antiport, the two molecules move in opposite directions, both of these could be linking energy cost with expenditure).
How does ATP provide energy?
ATP hydrolysis typically works by breaking the bonds to one phosphate in the ATP to phosphorylate proteins, this provides energy to drive the conformational change.
