Membrane Bilayer

Question 1

Roughly what percentages of the membrane bilayer are protein, lipids?

Answer 1

Protein- 60%, lipid- 40%

Question 2

What are unsaturated fatty acids?

Answer 2

Have a double bonded carbon in the card on tail

Question 3

What are two other less common lipids?

Answer 3

Sphingomyelin and Glycolipids

Question 4

What differentiates sphingomyelin from other lipids?

Answer 4

They have no glycerol backbone

Question 5

What are the most common/predominant type of lipid in bilayers?

Answer 5

Phospholipids

Question 6

Name two different types of Glycolipids and why they’re different?

Answer 6

Cerebroside (has 1 sugar attached) and ganglioside (has oligosaccharide attached)

Question 7

What is the most common length of fatty acid tail for phospholipids?

Answer 7

14-24 carbons

Question 8

List the functions of the membrane bilayer

Answer 8

Barrier, communication, signal generation in response to stimuli

Question 9

What properties do lipids in membrane bilayers show?

Answer 9

Flexion, rotation, lateral diffusion, flip flop (rare)

Question 10

What is lipid flip flop?

Answer 10

Where a phospholipid swaps lamellae. Very rare as its very thermodynamically unfavourable

Question 11

In what way(s) does cholesterol affect membrane fluidity?

Answer 11

Forms H bonds with FA tails, TF less packing, TF ^ fluidity. Also decreases fluidity because less FA flexion can occur

Question 12

What properties have cholesterol?

Answer 12

Polar head group, rigid, planar steroidal ring structure, non-polar tail

Question 13

What movements can proteins in the membrane bilayer do?

Answer 13

Rotation, lateral diffusion, conformational change. NOT FLIP FLOP

Question 14

In what ways can membrane proteins prevent motility/restrict movement?

Answer 14

Aggregation, tethering (to eg cytoskeleton), interaction (stabilises structure of tissues)

Question 15

What differentiates peripheral and integral proteins?

Answer 15

Peripheral are bound to the surface not embedded in it, whereas integral ones are embedded in it or pass through it

Question 16

What forces hold peripheral/extrinsic proteins in place? What can ‘break’ these?

Answer 16

H bonds, electrostatic forces, broken by changes in pH/ionic strength

Question 17

What holds integral/intrinsic proteins in place? What breaks this?

Answer 17

Interaction with hydrophobic bits of bilayer, removed by agents that compete for non-polar interactions (eg detergent)

Question 18

Why is flip flop so thermodynamically unfavourable?

Answer 18

It requires a hydrophilic head of the phospholipid to pass through a very strongly hydrophobic region to reach the other hydrophilic region.

Question 19

What conformation are transmembrane proteins most commonly?

Answer 19

Alpha-helical

Question 20

What makes up the cytoskeleton?

Answer 20

Spectrin, actin, Akyrin, Band 3 proteins. Band 3 protein bound to Akyrin bound to spectrin. Band 4.1(?) bound to actin bound to spectrin

Question 21

What are two haemolytic anaemias? How are they treated?

Answer 21

Hereditary spherocytosis, hereditary elliptocytosis. Regular blood transfusions

Question 22

What is hereditary spherocytosis? What causes it?

Answer 22

Mutation causes deficiency in Spectrin, RBC round up to spherical shape, less resistant to lysis, cleared by spleen TF RBC count drops

Question 23

What is hereditary elliptocytosis? What causes it?

Answer 23

Defect in Spectrin TF cytoskeleton can’t assemble correctly, form ellipsoid cells, v fragile and lyse

Question 24

Which is a defect in spectrin and which is a deficiency in spectrin?

Answer 24

Deficiency- hereditary spherocytosis. Defect- hereditary elliptocytosis

Question 25

Phospholipid fatty acid side chains are attached to which number carbons on glycerol?

Answer 25

C1 and C2

Question 26

What can be employed as head groups on a phospholipid?

Answer 26

Choline, amines, amino acids, sugars

Question 27

What conformation are double bonds in fatty acids present in?

Answer 27

Cis

Question 28

What will result when you introduce a double bond into a fatty acid chain?

Answer 28

Their ability to form 2D crystals decreases

Question 29

Where do cholesterol molecules hydrogen bond to in phospholipids?

Answer 29

The double bonded O in their ester bond

Question 30

With what forces can peripheral proteins be bound to the surface with?

Answer 30

Electrostatic forces, hydrogen bond interactions, disulphide bonds.

Question 31

Membrane spanning domains of membrane proteins are usually …..AA’s in length?

Answer 31

Between 18 and 22

Question 32

What secondary structure do membrane spanning domains of membrane proteins usually form?

Answer 32

Alpha-helix