Membranes And Membrane Protiens

Question 1

What is different in prokaryotic and eukaryotic membranes

Answer 1

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

Question 2

How does cholesterol affect membrane fluidity

What do we do to avoid this

Answer 2

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

Question 3

If frap what happens to the slope on the graph of its a more fluid membrane

Answer 3

Higher slope, faster recovery, more fluid

Question 4

What do lipid bylayers not let through

Why

Answer 4

They’re impermeable to ions and most polar molecules

This allows for ion concentration gradients across the membrane

Question 5

What’s least permeable to a bilayer

Answer 5

Na k cl-

Then

Glucose, tryptophan, urea/glycerol

Then (most permeable)

Indole, h20

Question 6

What is the purpose of lipid modifications of protiens

Answer 6

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)

Question 7

How is cysteine modified by a lipid

What happens to it

Answer 7

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

Question 8

What is a gpi anchor

Answer 8

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

Question 9

What is the role of membrane protiens

Answer 9

To help the plasma membrane conduct traffic of molecules into and out of cells

Question 10

What the first way membrane protiens cross the membrane

Give an example of a membrane protien and what it does

Answer 10

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

Question 11

Where do nonpolar alpha helices of protiens interact

Answer 11

With the nonpolar hydrocarbon core of the lipid membrane

Question 12

What’s another way membrane protiens cross the lipid bilayer

Answer 12

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”

Question 13

What’s an example of a protien that is not fully inside the membrane

Answer 13

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

Question 14

What does Prostaglandin H2 synthase 1
Do

Answer 14

It catalyzes the conversion of arachidonic acid to Prostaglandin H2, has a serine residue

Prostaglandin H2 promotes inflammation and modulates gastric acid secretion

Question 15

What does arachidonic acid do to get converted

Answer 15

It moves from the lipid membrane to the active site of the Prostaglandin H2 synthase 1 enzyme

through use of a hydrophobic channel

Question 16

What do drugs like aspirin do to Prostaglandin H2 synthase 1 enzyme

Answer 16

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

Question 17

What is the na k atp-ase

Answer 17

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

Question 18

What is the sodium glucose linked transporter

Answer 18

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

Question 19

What is the potassium ion channel

How does it select

Answer 19

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

Question 20

How does potassium move through the k ion channel pore

Answer 20

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

Question 21

What is the radius of potassium

Answer 21

1.33 A

Question 22

When solvated water does ____

When desolvated the oxygen does ____

To the K

Answer 22

Cubic coordination

Octahedral binding

Question 23

How do things that are smaller than potassium but aren’t potassium not get sent through the K ion channel

Answer 23

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

Question 24

How does the k ion channel work

Answer 24

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