Session 1 - The Membrane Bilayer

Question 1

Where are phospholipids synthesised?

Answer 1

Endoplasmic reticulum

Question 2

Which 4 types of molecules can be employed as head groups on phospholipids?

Answer 2

Choline, amines, amino acids and sugars

Question 3

Which 2 fatty acid side chain lengths are most common in naturally occurring phospholipids?

Answer 3

C16 and C18

Question 4

Double bonds in fatty acid side chains of naturally occurring phospholipids are in which conformation?

Answer 4

Cis

Question 5

What effect does the introduction of double bonds into phospholipids fatty acid chains have?

Answer 5

Decreases the ability of the phospholipids to form two-dimensional crystals

Question 6

What is the least thermodynamically favourable mode of phospholipid mobility in a membrane?

Answer 6

Flip-flop

Question 7

Which modes of mobility are permitted in membrane lipids?

Answer 7

Rotational movement, vibrational movement, lateral diffusion and flip-flop movement

Question 8

How does cholesterol bond to phospholipid molecules?

Answer 8

Cholesterol hydroxyl groups form hydrogen bonds with the double bonded oxygen atoms in the ester bonds of the phospholipid molecules

Question 9

What is the typical ratio of cholesterol to phospholipid molecules in a membrane?

Answer 9

1:1 ratio

Question 10

What effect does cholesterol have on membrane fluidity and why?

Answer 10

Reduces membrane fluidity because it reduces the phospholipid fatty acid side chain’s mobility

Question 11

How can integral transmembrane proteins move within a membrane?

Answer 11

Via conformational changes, fast axial rotation or fast lateral diffusion

Question 12

How can peripheral membrane proteins be bound to the surface of a membrane?

Answer 12

Via electrostatic interactions; hydrogen bonding; or disulphide bonding

Question 13

How can peripheral membrane proteins be removed from a membrane?

Answer 13

By modifying pH or modifying ionic strength

Question 14

How can integral membrane proteins be removed from a membrane?

Answer 14

Using solvent extraction or detergent extraction

Question 15

Integral membrane proteins interact extensively with which regions of a membrane bilayer?

Answer 15

Hydrophobic regions

Question 16

The membrane spanning domains of membrane proteins are usually formed by which secondary structure?

Answer 16

Alpha helix

Question 17

Where are mitochondrial membrane proteins synthesised?

Answer 17

In the cytoplasm

Question 18

Where does membrane protein biosynthesis begin?

Answer 18

In the cytoplasm

Question 19

What type of it all sequence do lysosomal membrane proteins have?

Answer 19

Hydrophobic

Question 20

How is the arrest of membrane protein biosynthesis mediated?

Answer 20

By the binding of signal recognition binding proteins

Question 21

Which part of the ER recognises the SRP on a protein?

Answer 21

The docking protein

Question 22

How are membrane protein-synthesising ribosomes anchored to the ER?

Answer 22

Using ribophoryns

Question 23

How is passage of membrane proteins through the ER arrested?

Answer 23

Using a stop transfer sequence on the protein

Question 24

What usually follows the stop transfer sequence on the C-terminal side of a protein?

Answer 24

Two basic residues

Question 25

How is a core carbohydrate group transferred to a newly synthesised membrane protein?

Answer 25

From a dolichol phosphate carrier lipid

Question 26

What catalyses formation of disulphide bonds in post-translational processing of proteins?

Answer 26

Protein disulphide isomerase

Question 27

Where are disulphide bonds formed in post-translational modification?

Answer 27

In the ER

Question 28

Where do the final post-translational carbohydrate modifications of proteins occur?

Answer 28

In the trans-Golgi

Question 29

What is required to target newly synthesised membrane proteins to lysosomes?

Answer 29

Glycosylation

Question 30

In phospholipids, which atoms on the glycerol backbone are fatty acid side chains attached to?

Answer 30

C1 and C2