Lecture 14 - Membrane structure

Question 1

what are membranes composed of?

Answer 1

lipids and proteins

Question 2

True or False:

Membranes vary in their lipid:protein ratio

Answer 2

True

Question 3

What’s the lipid:protein ratio of the plasma membrane?

Answer 3

equal

Question 4

What type are most lipids?

Answer 4

glycerophospholipids

Question 5

What are glycerophospholipids made of?

Answer 5

1) glycerol 3-P (simple carb)
2) 2 fatty acid acyl chains (with acyl gps)
3) extra gp attached to phosphate gp

Question 7

1) What’s an acyl gp?
2) What’s the purpose of the extra gp?
3) which part is hydrophobic, non-polar?
4) which part is hydrophilic, polar?

Answer 7

1) FA without its hydroxyl gp at its carboxyl terminal
2) gives it it’s special character; unique
3) tail
4) head

Question 8

What is a cardiolipin?

Answer 8

two glycerophospholipids bridged together at the top by another glycerol gp

Question 9

What is the name of one of the most important lipids as far as metabolic regulation?

What does it have to make it unique?

What is it used in in relation to metabolism?

Answer 9

Phosphatidylinositol

Insoitol ring at the top bonded to P gp –> inositol ring can be phosphorylated

used metabolically in signaling processes

Question 10

Name the major FA in membrane lipids = # of Cs, if its saturated or unsaturated and # of dbl bonds

Answer 10

1) Palmitic acid = C16, saturated
2) Stearic acid = C18, saturated
3) Oleic acid = C18, cis unsaturated, 1 dbl bond
4) Linoleic acid = C18, cis unsaturated, 2 dbl bonds
5) Linolenic acid = C18, cis unsaturated, 3 dbl bonds
6) Arachidonic acid = C20, cis unsaturated, 4 dbl bonds

Question 11

True or False:

Lipids are stationary rigid structures.

Answer 11

False

Lipids are wobbling around, rotating around

Question 12

What do double bonds do for the FA

Name the two forms

Answer 12

give the FA additional structure

Cis dbl bond - puts kink in structure

Trans dbl bond - makes more rigid

Question 13

What is a sphingosine?

What is it made of?

Answer 13

one of the special gps that can be attached to a FA

top gp with a long non-polar FA tail; add gps to sphingosine to make shingolipids

Question 14

What’s a sphingolipid

What’s a ceramide?

What’s a sphingomyelin?

What’s a glycosphingolipid?

What’s a cerebroside?

Answer 14

Sphingosine with an additional FA gp

a sphingolipid

sphingolipid with a choline gp attached at the top to the phosphate gp

sphingolipid with a sugar attached at top

a glycophingolipid with specifically a galactose attached at the top –> interact with water better; signaling

Question 15

Describe cholesterol and its relation to membrane structure

Answer 15

1) Cholesterol has lots of hydrophobic parts that point down
2) has a hydroxyl gp that sticks out which makes it polar and is also the attachment site for other functional gps/mols; it also adds character to the mol
3) Cholesterol is incorporated into the membrane

Question 16

Describe lipid compositio in membranes

Answer 16

1) varied lipid composition in different membranes
2) mainly glycerophospholipids
3) individual phospholipid categories - mainlyphosphatidylcholine

Question 17

Describe phospholipid distribution btw inner and outer layers of phospholipid bilayer

Name three enzymes involved with the phospholipid bilayer and thir function

Answer 17

Lipids on outer leaflet have a different composition that lipids on inner leaflet (cytoplasm)

Flippase, Floppase, Scramblase - responsible for generating and maintaining composition of bilayer

Question 18

Name and describe membrane proteins

Answer 18

1) Integral membrane/transmembrane proteins - proteins that pass through entire membrane
2) Peripheral membrane proteins - connected to one side of lipid bilayer –> associate through charges (AA side chains, polar head gps) or some sort of lipid

*interact with other membrane proteins

Question 19

True or False:

transmembrane alpha helixes predicted by side change hydrophobicity

Answer 19

True

where there’s more hydrophobic AAs –> more likely to form transmembrane proteins

Question 20

What’s an aquaporin?

Answer 20

membrane protein that allows water to pass through the membrane; in center is the core that allows water to pass

Question 21

Name the three different ways a peripheral membrane protein can attach to the membrane

Answer 21

1) By a oligossacharide - COOH gp
2) by covalent bond between N of protein and C of lipid
3) by a cysteine side chain - sulfhydril bond

Question 22

Explain how temperature can affect membrane lipid motion

Explain affect of dbl bonds on nmotion

Answer 22

1) Above transition temperature - swinging around very rapidly
2) below transition temperature - motions cease
3) nature of tails influence motion (presence of cis/trans dbl bonds)
4) more trans dbl bonds = less motion; more cis dbl bonds = more motion
5) proteins are the structures doing the functions –> must maintain that motion to function effectively

Question 23

1) define membrane fluidity
2) Discuss membrane fluidity
3) What are the primary factors
4) what does increased membrane cholesterol content affect?
5) what does altering membrane fluidity affect?

Answer 23

1) indicates the relative rates of motion of the lipid constituents
2) it is a function of the composition of the membrane
3) FA chain length, extent of saturation and cholesterol content are primary factors
4) increased membrane cholesterol content during disease affects fluidity

* so can presence of foreign mols like ethanol

*so can lipid peroxidation

5) altering membrane fluidity in turn can alter the function of the proteins embedded in the membrane

Question 24

What are microdomains?

What’s another name?

What are they made of?

Answer 24

certain proteins attract certain types of membrane constituents

rafts –> lipid rafts attracted to particular proteins (float around)

cholesterol and sphingolipids