Membrane Structure and Dynamics

Question 1

list 3 ways in which membrane proteins associate with the lipid bilayer

Answer 1

• integral membrane proteins: consists of and alpha helix or a B barrel
• lipid-linked proteins: have covalently attached prenyl group, fatty acyl group
• peripheral membrane proteins: interact noncovalently with proteins/lipids at the membrane surface

Question 2

are lipids distributed evenly across a membrane?

Answer 2

no, they may form rafts

Question 3

what does the secretory pathway discuss?

Answer 3

the transmembrane passage of membrane and secreted proteins

Question 4

• bring membranes together and help mediate vesicle fusion

Answer 4

SNARE’s

Question 5

what is a micelle

Answer 5

aggregate of single tailed lipids

Question 6

how are micelles formed?

Answer 6

it is driven by hydrophobic effect - water minimizes its contacts with hydrophobic molecules.

Question 7

what are liposomes

Answer 7

a suspension of phospholipids can form liposomes, their diameters depend on lipid composition, solvent used and mechanical extrusion

Question 8

explain phase transition in lipid bilayer

Answer 8

the transition temp. increases with the chain lenght, and degree of saturation.

• above the transition temperature its in liquid crystal phase
• below temp. its in gel-like solid phase

Question 9

give 3 functions of membrane proteins

Answer 9

• catalyse chemical reactions
• transporters
• receptors

Question 10

integral proteins are - oriented

Answer 10

asymmetrically

Question 11

what is the secondary structure of the transmembrane segments

Answer 11

• for a polypeptide chain to penetrate the lipid bilayer it must have hydrophobic side chains to contact the lipid tails
• this requirement is met by formation of secondary structures that satisfy the H bond capacity of the polypeptide backbone

Question 12

name the transmembrane proteins that contain alpha helices

Answer 12

• halobacterium salinarum bacteriorhodopsin

Question 13

name the transmembrane proteins that contain beta sheets

Answer 13

E. coli OmpF porin.
an antiparallel sheet rolls to form a barrel. The number of B strands must be even.
Happen in porins

Question 14

what is the most common prenylation site (occurs in lipid linked proteins)

Answer 14

c terminal sequence whit Cysteine and an aliphatic aa, and a residue Y which : if Ala, Met, Ser is faresylated. Or if Leu is geranylated.
In both its a thioether bond

Question 15

what are the 2 kinds of fatty acids linked to membrane proteins

Answer 15

• mysristic acid: attached via amide linkage to N terminal Gly
• palmitic acid: linked via thioester bond with Cys

Question 16

myristolation

Answer 16

is stable, and these proteins are ubiquitous

Question 17

palmitoylation:

Answer 17

is dynamic, can be removed by palmitoyl thioesterases. Are found on cytoplasmic side of plasma membrane - where they participate in signaling

Question 18

what is the role of spectrin

Answer 18

accounts for 75%of the erythrocyte membrane skeleton

- folds into triple stranded alpha helical coiled coils

Question 19

what is the role of ankyrin

Answer 19

associates with spectrin, and ion channels + integral membrane proteins.

• provides attachment sites to anchor membrane skeleton to membrane
• right handed helical stack, with concave surface

Question 20

where are membrane lipids synthesized

Answer 20

• SER
• in prokaryotes (the cytoplasmic face of plasma membrane
• in all cells, new membranes are generated by the expansion of existing ones

Question 21

flappases

Answer 21

cause flip flop of specific phospholipids. Uses facilitated diffusion

Question 22

phospholipid translocases

Answer 22

transport specific phospholipids across a bilayer using active transport

Question 23

translocon

Answer 23

helps signal peptide cross the membrane

Question 24

clathrin coated vesicles

Answer 24

transport transmembrane, GPI linked and secreted proteins from the golgi to the plasma membrane

Question 25

COP1 coated vesicles

Answer 25

Carry out both the anterograde and retrograde transport of proteins between successive Golgi compartments. Also, they return escaped ER-resident proteins from the Golgi back to the ER. The COPI protomer contains seven different subunits.

Question 26

COPii coated vesicles

Answer 26

Transport proteins from the ER to the Golgi. COPII vesicles components are then returned to the ER by COPI-coated vesicles. The COPII protein is made of two heterodimers

Question 27

purpose of mannose 6 phosphate

Answer 27

is a lysosome targeting signal

Question 28

purpose of Cterminal sequences, COPI, COPII

Answer 28

are ER targeting signals