Membrane Proteins

Question 1

What are the THREE classes of membrane proteins?

Answer 1

1. Integral
2. Lipid-Anchored
3. Peripheral

Question 2

How do Integral Proteins attach to the membrane?

Answer 2

Spans the bilayer

Question 3

How do Lipid-Anchored Proteins attach to the membrane?

Answer 3

Covalently bound to lipids

Question 4

How do Peripheral Proteins attach to the membrane?

Answer 4

Indirectly associate with membrane via non-covalent interactions with lipid head or other membrane proteins

Question 5

How many hydrophobic amino acids are associated with the Integral membrane protein membrane spanning region?

Answer 5

20-25

Question 6

What do Hydropathy plots predict?

Answer 6

Transmembrane helices of Integral Proteins

Question 7

How long is the α-helix in the membrane spanning region of Integral proteins?

Answer 7

3-4nm

Question 8

Which class of Integral membrane protein has its amino terminus in the cytosol?

Answer 8

Type II

(all other types have carboxyl terminus in cytosol)

Question 9

What is the difference between Type I and Type III Integral membrane protein?

Answer 9

Type I has a signal sequence that is cleaved during insertion into the membrane

Question 10

What is the structural difference of Porins compared to other transmembrane proteins?

Answer 10

Barrel shape comprised of 16 β-stands that span membrane

Question 11

What is CMC?

Answer 11

Critical Micelle Concentration

Question 12

What happens to detergents above and below CMC?

Answer 12

• BELOW CMC - detergents dissolve as single molecules in water
• ABOVE CMC - detergent molecules cluster to form micelles

Question 13

What are Detergents used in purifying membrane proteins?

Answer 13

• Amphipathic molecules
• Solubilise lipids and membrane proteins

Question 14

What are the characteristics of Ionic detergents?

Answer 14

• Charged
• Disrupts hydrogen and ionic bonds
• Denature proteins at high concentrations

Question 15

What are the characteristics of Non-Ionic detergents?

Answer 15

• Don’t denature proteins
• Useful in purification of membrane proteins

Question 16

Which side of the cellular membrane do GPI-linkages occur?

Answer 16

Extracellular side

Question 17

Which side of the cellular membrane does Acylation and Prenylation occur?

Answer 17

Cytosolic side

Question 18

What is Acylation?

Answer 18

FA attached to protein

Question 19

What is the carbon skeleton of Myristic acid?

Answer 19

14:0

Question 20

What is the carbon skeleton of Palmitic acid?

Answer 20

16:0

Question 21

Which amino acid does Palmitoylation occur on?

Answer 21

Internal Cys (or Ser)

Question 22

Which amino acid does Myristolation occur on?

Answer 22

N-terminal Gly

Question 23

What is an example of a gene that undergoes Acylation by Myristoylation?

Answer 23

v-Src oncogene

Question 24

What is the structure of Farnesyl?

Answer 24

C15, 3x Isoprenes

Question 25

What is the structure of Geranylgeranyl?

Answer 25

C20, 4x Isoprenes

Question 26

Which amino acid does Farnesyl OR Geranylgeranyl attach to?

Answer 26

Cys at/near C-terminus

Question 27

What is the attachment sequence of Farnesyl OR Geranylgeranyl?

Answer 27

Cys-Φ-Φ-X (Φ = hydrophobic aa)

Question 28

What is an example of enzymes that undergoes Prenylation?

Answer 28

* Small GTPases * Ras, Rab etc

Question 29

How is GPI linked to a membrane protein?

Answer 29

Linked to C-terminus of protein via Phosphoethanolamine

Question 30

What is an example of an enzyme that undergoes GPI linkage?

Answer 30

Placental Alkaline Phosphatase (PLAP)

Question 31

TRUE OR FALSE: Carbohydrates can only be attached to membrane proteins

Answer 31

False. Can be attached to both membrane proteins AND lipids

Question 32

What are carbohydrates attached to lipids called?

Answer 32

Glycolipids * attached to glycerol or sphingosine backbone

Question 33

What are large polysaccharide sugars attached to membrane proteins called?

Answer 33

Proteoglycans

Question 34

What are small oligosaccharides attached to membrane proteins called?

Answer 34

Glycoproteins

Question 35

On which THREE amino acids does Glycosylation occur on Glycoproteins / Proteoglycans?

Answer 35

* Serine * Threonine * Asparagine

Question 36

Which side of the membrane does Glycosylation occur?

Answer 36

Only occurs on the exoplasmic side of the membrane