Lecture 1

Question 1

Define the membrane according to the fluid mosaic model:

Answer 1

A two dimensional sea of mobile lipid in which proteins diffuse (or float)

Question 2

Define steroids in the PM:

Answer 2

Cholesterol and its esters, amphipathic, with a relatively large C-H portion.

Question 3

Describe phosphatidylserine:

Answer 3

Is normally found on the inner surface of the PM but during apoptosis it flips on the EC surface.

Question 4

How is the bilayer structure stabilized once formed?

Answer 4

By tail-tail and head-head interactions.

Question 5

Define integral (intrinsic) membrane proteins:

Answer 5

One or more regions are embedded in the PM and most are transmembrane proteins.

Question 6

Define peripheral membrane proteins:

Answer 6

Attached to the membrane through membrane proteins or lipids (can be exo or endofacial).

Question 7

What are the function performed by single spans transmembrane proteins

Answer 7

Anchoring Receptor-Transducer function

Question 8

What are the functions performed by multiple spans transmembran proteins:

Answer 8

They may form an aqueous pore in the membrane to form channels and transporters.

Question 9

What are the three classes of transmembrane proteins according to the number of spans?

Answer 9

Single span Multiple spans Multimeric protein complexes

Question 10

What are the three types of net charge that an amino acid residue can have in a membrane protein?

Answer 10

Neutral (Zwitterionic) Cationic (Lysine, Arginine, ‘Basic’) Anionic (Glutamate, Aspartate, ‘acidic’)

Question 11

What function do His-322 and Glu-325 in proton-lactose symporter perform?

Answer 11

They are involve in proton transport

Question 12

What functions do Ala-177 and Tyr-236 in proton lactose symporter perform?

Answer 12

They are important in binding and transporting lactose.

Question 13

What physical structure of the bilayer did X-ray and neutron diffraction data revealed?

Answer 13

60% lecithin and 40% cholesterol.

Question 14

What is the rate of fluorescence recovery in FRAP proportional to?

Answer 14

It is proportional to the rate of protein diffusion in the membrane region and thus to the diffusion coefficient.

Question 15

What does FRAP stand for?

Answer 15

Fluorescence recovery after photobleaching

Question 16

What are the three mechanisms by which substances can cross the plasma membrane?

Answer 16

Diffusion Osmosis Tranport (facilitative or active)

Question 17

What are the three functions that occasional charged residue within transmembrane domains may have?

Answer 17

1) Stabilising structure 2) Binding substrate 3) Charge transfer

Question 18

What favours the sol (fluid) phase?

Answer 18

Presence of short fatty acid and double bond in the chain.

Question 19

Who first coined the term fluid mosaic model?

Answer 19

Singer and Nicholson, in 1972.

Question 20

What are the two main classes of cell membranes?

Answer 20

Plasma membran and Internal Membrane

Question 21

What does the membrane contains?

Answer 21

1) Lipids 2) Proteins 3) Carbohydrate (Glycolpids and Glycoproteins)

Question 22

What are the four different types of lipids found in the membrane?

Answer 22

1) Phospholipids 2) Steroids 3) Neutral fats (glycerides) 4) Glycolipids

Question 23

Describe glycolipids:

Answer 23

Minor, include antigens and have a carbohydrate as a head group.

Question 24

What determines fluidity of the membrane?

Answer 24

Heat and lipid composition.

Question 25

Describe transmembrane domains property?

Answer 25

They are likely to be regions rich in hydrophobic amino acids residues anchored by interactions with phospholipids tails.

Question 26

What are the four techniques used to determine membrane structure?

Answer 26

1) Lipid area (unimolecular film) 2) X-Ray and Neutron Diffraction 3) Transmission Elecctron Microscopy 4) Freeze-etching.

Question 27

Describe the motifs that are found in transmembrane regions of integral proteins:

Answer 27

20-25 amino acids residues forming alpha-helix; polar peptide linkages form shielded H-bonds within the helix, the helix neutralizes the polar character of peptide bonds.

Question 28

What are the three techniques used to determine dynamics of membranes?

Answer 28

1) Electron spin resonance spectroscopy 2) Phase transition 3) Protein tagging (cell fusion, electric field, FRAP)

Question 29

Describe some membrane proteins that are immobile:

Answer 29

Glycophorin and protein 3 interact with elements of cytoskeleton that lies beneath PM.

Question 30

Describe the structure of ankyrin, spectrin and actin:

Answer 30

They interact with membrane proteins or with each other to form a supercomplex