Biological Membranes

Question 1

Definition of a complex lipid

Answer 1

A lipid with multiple parts

Question 2

Purpose of a head group

Answer 2

To allow amphipathic capacity

Question 3

Definition of amphipathic

Answer 3

A molecule having both hydrophobic and hydrophillic parts

Question 4

Basic structure of sphingolipids

Answer 4

A sphingosine (long chain alcohol), a fatty acid (attaching via acyl group), and a polar head group

Question 5

X group of ceramide

Answer 5

None

Question 6

X group of sphingomyelin

Answer 6

phospho-choline

Question 7

X group of lactosyl-ceramide

Answer 7

> 1 saccharide

Question 8

X group of neutral glycolipid

Answer 8

Glucose

Question 9

X group of ganglioside

Answer 9

Complex saccharide, including various types of branching

Question 10

Cholesterol size, typology, building blocks, place of biosynthesis

Answer 10

27 carbons, planar typology (can be stacked), built from carbon units of acetyl-CoA, synthesized by all cells (mainly the liver) in the cytosol

Question 11

How are micelles formed

Answer 11

By fats and detergents; the head group is larger, so the chemicals wrap around to form balls easily. Only a single fatty acid tail.

Question 12

How are liposomes formed

Answer 12

By phospholipids; the two fatty acid tails cause no difference between the head group and the tail group, so the curvature is slight and a bilayer is formed.

Question 13

Issues with early view of biomembranes

Answer 13

1) Didn’t consider heterogenity of components, as each layer may be made up of different components
2) Didn’t consider heterogenity of protein insertion, as each layer may have different proteins
3) Leaflet asymmetry (leaflets being glycolipids, oligosaccharides, etc.)
4) Motional restrictions inherent in the layer (not just fluid)
5) Interaction with the cytoskeleton

Question 14

Most abundant biological lipid

Answer 14

Cholesterol, ~20%

Question 15

Relative concentration of sphingomyelin and phosphatidylcholine

Answer 15

50/50

Question 16

Phosphatidylserine composition and role

Answer 16

Nearly 10%, relatively high, used for signalling

Question 17

Are lipids glycosylated

Answer 17

Yes, extensively

Question 18

Why membranes are asymmetric (why are the two membranes comprising the bilayer different?)

Answer 18

Facilitates association / integration of membrane proteins, provides membrane curvature, and provides correct localization of signalling molecules

Question 19

Name three kinds of enzymes that mediate membrane asymmetry

Answer 19

Flippases, floppases and scramblases

Question 20

Main phospholipids on outside surface of membrane in erythrocytes

Answer 20

Phosphatidylcholine and sphingomyelin

Question 21

Main phospholipids on inside of membrane in erythrocytes

Answer 21

Phosphatidylethanolamine and phosphatidylserine

Question 22

Term for ‘ lipid rafts’ on membrane

Answer 22

Mini-domains

Question 23

Main composition of mini-domains

Answer 23

Cholesterol and sphingolipids with long acyl lengths

Question 24

Phase of lipids in mini-domains

Answer 24

Ordered; becomes more rigid.

Question 25

Size and timespan of mini-domains

Answer 25

10-300nm, short-lived

Question 26

Protein composition of mini-domains

Answer 26

Caveolae proteins, theoretically for a structural role, GPI-anchored proteins

Question 27

Advantage rafts have with proteins

Answer 27

Localizing proteins for related processes can help accomplish that process, such as for signalling

Question 28

Name four ways to aggregate proteins for lipid rafts

Answer 28

(1) Protein-protein coupling
(2) Protein-lipid coupling
(3) Extracellular matrix
(4) Cytoskeleton

Question 29

What aggregation does to proteins

Answer 29

Affects motion and localization of the proteins

Question 30

Types of lateral movement in proteins

Answer 30

(1) Transient confinement by obstacle clusters
(2) Transient confined by the cytoskeleton, which acts like a fence
(3) Directed motion by attachment to the cytoskeleton
(4) Free and random diffusion in the membrane plane

Question 31

Which phospholipid, out of sphingosine, sphingomyelin, neutral glycolipids, lactosyl-ceramide, ceramide and ganglioside has a fatty acid (amide) residue?

Answer 31

All except sphingosine.

Question 32

Which phospholipid, out of sphingosine, sphingomyelin, neutral glycolipids, lactosyl-ceramide, ceramide and ganglioside, has a polar X group?

Answer 32

All except sphingosine and ceramide.