Membranes And Membrane Protiens Flashcards
What is different in prokaryotic and eukaryotic membranes
The eukaryotes membranes have lipids and protiens and carbs can be attached to them
They have a bunch of organelles inside
Prokaryotes have a two or one very thick cell walls and no organelles
How does cholesterol affect membrane fluidity
What do we do to avoid this
At low temps the rigid hydrophobic ring cause the membrane to be thicker and less fluid
Need to heat more to make it more fluid because it’s less effective at higher temps
If frap what happens to the slope on the graph of its a more fluid membrane
Higher slope, faster recovery, more fluid
What do lipid bylayers not let through
Why
They’re impermeable to ions and most polar molecules
This allows for ion concentration gradients across the membrane
What’s least permeable to a bilayer
Na k cl-
Then
Glucose, tryptophan, urea/glycerol
Then (most permeable)
Indole, h20
What is the purpose of lipid modifications of protiens
The lipids change the biochemical properties of the protien
(ex. Adding protiens to lipids can anchor the protiens to the membranes surface because lipids are inserted into the membrane)
They allow for association of the protien with a hydrophobic environment (the membrane)
How is cysteine modified by a lipid
What happens to it
A palmitoyl (lipid) group is attached to the cystien by a thioester bond
Or a farnesyl group is attached to the cysteine by a thioether bond and the carboxyl group of the protien has a methyl
Without the lipid the cysteine is polar, with it the protien gets anchored to the membrane
What is a gpi anchor
It is a glycolipid attached to the carboxy terminus of the protien via an amide (NH) bond
Bind to the protien and the lipid to abhor the protien to the membrane
What is the role of membrane protiens
To help the plasma membrane conduct traffic of molecules into and out of cells
What the first way membrane protiens cross the membrane
Give an example of a membrane protien and what it does
They use alpha helices that interact with the nonpolar hydrocarbons tails of the lipids
Ex bacteriorhodopsin uses light energy to move protons from the inside of the cell to the outside
This makes a proton gradient which can make atp
Where do nonpolar alpha helices of protiens interact
With the nonpolar hydrocarbon core of the lipid membrane
What’s another way membrane protiens cross the lipid bilayer
They use beta strands in the shape of a beta barrel
This makes a single beta sheet with a pore in the centre
And example of this is “porin”
What’s an example of a protien that is not fully inside the membrane
Prostaglandin H2 synthase 1
It’s bound to the outer membrane of the endoplasmic reticulum and has only a small hydrophobic part that gets embedded into the membrane
What does Prostaglandin H2 synthase 1
Do
It catalyzes the conversion of arachidonic acid to Prostaglandin H2, has a serine residue
Prostaglandin H2 promotes inflammation and modulates gastric acid secretion
What does arachidonic acid do to get converted
It moves from the lipid membrane to the active site of the Prostaglandin H2 synthase 1 enzyme
through use of a hydrophobic channel
What do drugs like aspirin do to Prostaglandin H2 synthase 1 enzyme
They block the hydrologic channel by having the aspirin donate an acetyl group to the ser 530 in the channel
This makes it so the arachidonic acid can’t come in and get converted
What is the na k atp-ase
Atp is hydrolyzed to make 3 na molecules move out of the cell to the higher concentration,
Moves 2 k into cell where their concentration is higher
What is the sodium glucose linked transporter
The na gradient cause by the na k atp-ase causes na to go back into the cell down its gradient
This give energy to also move glucose into the cell but against its gradient
Symporter
What is the potassium ion channel
How does it select
Is transport potassium ions specifically and quickly
The hydrophilic gap for ions to pass through the membrane gets narrower as it goes closer to the outside of the cell.
This allows for the selectivity filter where ions with radius larger than 1.5A can’t pass though the pore and out of the cell
How does potassium move through the k ion channel pore
It first has a solvation shell of water that let us move through the pore
After it reaches the selectivity filter, it’s forced to lose this shell and instead interact with the oxygen atoms of the pore protiens AA side chains
The energy released to bind to oxygen is more than the energy cost to desolvate, so desolvation is more favourable
What is the radius of potassium
1.33 A
When solvated water does ____
When desolvated the oxygen does ____
To the K
Cubic coordination
Octahedral binding
How do things that are smaller than potassium but aren’t potassium not get sent through the K ion channel
The sodium ion have size of 0.95A
They still have to lose their solvation shell the pass through the filter
But the energy to resolvate and bind to oxygen in the filter is less than the energy to desolvate
So they stay in the solvated state and don’t pass through
How does the k ion channel work
4 spots
2 k ions go in, the repel each other so the top on moves up one
This opens a site for the bottom one to move up so it does, but the the top on get shifted up again to the 4th position
Another k ion comes in and the one at the 4th pops out of the cell due to repulsion
