02_Membranes of the Cell

Question 1

What was the classical experiment that first deduced the lipid composition of membranes?

Answer 1

1890s, Overton: placed plant root hairs in different solutions with different solutes; lipophilic substances moved into root hair more readily than lipid-insoluble ones => boundary of cells must be lipid.

Question 2

What is the most studied cell membrane, and why? (4 points)

Answer 2

the membrane of the RBC, because:

• low cost and high abundance in blood
• already present as single cells and don’t need to be separated from complex tissue
• simple compared to other cells (no contaminating internal cell membranes)
• can obtain intact membranes (called ghosts) through osmotic shock and hemolysis

Question 3

What is a solution with a higher solute concentration than the cell cell called? What is the effect of placing a cell in this solution?

Answer 3

Hypertonic solution; net water loss => cell shrivels

Question 4

A cell is placed in solution and it swells; what kind of solution was this? (hyper/hypo/isotonic)

Answer 4

Hypotonic solution

Question 5

What kind of solution must RBCs be placed in to obtain ghosts?

Answer 5

Hypotonic solution

Question 6

How did Gorter & Grendel (1925) reach the conclusion that cells must have a double layer membrane?

Answer 6

They extracted lipids from RBC membranes, measures their surface area on water and compared this to surface area of an RBC. They found that the area covered ~twice the SA of an RBC => the membrane must be a bilayer.

Question 7

Who initially proposed the fluid mosaic model of cell membranes? Briefly describe the model.

Answer 7

Singer & Nicholson (1972)

lipid bilayer is fluid and able to move; proteins penetrate the bilayer, forming a mosaic.

Question 8

What can be found in the hydrophobic core of the lipid bilayer?

Answer 8

Hydrophobic proteins + acyl chains

Question 9

What is the approximate width of the lipid bilayer?

Answer 9

~30Å

Question 10

What are the three major classes of lipids making up eukaryotic membranes?

Answer 10

Glycerolipids, Sphingolipids, Sterols

Question 11

What is defined as carbon 3 on the glycerol backbone?

Answer 11

Where phosphate group attaches

Question 12

When the R group in a glycerolipid is choline, it is called __________

Answer 12

phosphatidylcholine (aka lecithin)

Question 13

What is the backbone in sphingolipids?

Answer 13

Sphingosine

Question 14

What is the R group in sphingomyelin?

Answer 14

Choline

Question 15

What are plant, fungi and animal sterols called?

Answer 15

Phytosterols, ergosterols, cholesterols

Question 16

Sphingolipids accept acyl chains through a(n) _______ bond.

Answer 16

amide

Question 17

What is the parent compound for ALL phospholipids?

Answer 17

Phosphatidic acid (a phosphomonoester)

Question 18

What is (usually) the net charge of the phosphate head group at physiological pH?

Answer 18

-

Question 19

Which phospholipid does PE stand for?

Answer 19

Phosphatidylethanolamine

Question 20

Which two phospholipids are abundant in mitochondrial membranes?

Answer 20

Phosphatidylglycerol

Diphosphatidylglycerol (aka cardiolipin – CL)

Question 21

Which phospholipids are neutral?

Answer 21

phosphatidylcholine & phosphatidylethanolamine

Question 22

Which phospholipids are more abundant in the cytosolic leaflet?

Answer 22

PS, PE, PI

Question 23

Which glycerolipids are NOT found in bacteria?

Answer 23

PI, PC

Question 24

What glycerol are glycerolipids in archaea based on?

Answer 24

glycerol-1-phosphote