Structure of the Cell Membranes

Question 1

What is the phospholipid head hydrophobic or hydrophilic?

Answer 1

Hydrophillic

Question 2

Is the phospholipid tail hydrophobic or hydrophillic?

Answer 2

Hydrophobic

Question 3

What is the phospholipid bilayer?

Answer 3

Two phospholipid molecules together with the heads facing out and the tails facing in.

Question 4

What does it mean if the phospholipid head is hydrophilic?

Answer 4

The head is attracted to water

Question 5

What does it mean if the phospholipid head is hydrophobic?

Answer 5

It is repelled by water

Question 6

What are the functions of the phospholipid bilayer?

Answer 6

• Allow lipid soluble substances to enter and leave the cell.
• Prevent water soluble molecules from entering/leaving the cell.
• Makes the membrane flexible and self sealing.

Question 7

What do protein channels do?

Answer 7

Allow water-soluble molecules to diffuse across the membrane.

Question 8

How do carrier proteins work?

Answer 8

Bind to ions/molecules then change shape to move these molecules across the membrane.

Question 9

Which proteins do you find on the cell-surface membrane?

Answer 9

• Structural proteins
• Channel proteins
• Carrier proteins
• Cell surface receptors

Question 10

What does cholesterol do when it is in the cell-surface membrane?

Answer 10

• Add strength to the membrane making it less fluid at high temperatures.
• Limit movement of phospholipids and other molecules by pulling the fatty acid tails together. (Still doesn’t make it too rigid).
• Cholesterol is very hydrophobic, preventing the leakage of water and dissolved ions from the cell.

Question 11

What does cholesterol allow the CSM to do when at high temperatures?

Answer 11

Stay less fluid

Question 12

How does cholesterol limit movement of phospholipids and other molecules?

Answer 12

Pull together the fatty acid tails of the phospholipid molecules.

Question 13

How does cholesterol prevent the leakage of water and dissolved ions from the cell?

Answer 13

As cholesterol is very hydrophobic

Question 14

What are glycolipids made of?

Answer 14

Carbohydrates covalently bonded with a lipid.

Question 15

What are the functions of glycolipids?

Answer 15

• Act as recognition sites
• Maintains stability of the membrane
• Helps cells to attach to each other to form tissues.

Question 16

How do glycoproteins act as recognition sites?

Answer 16

The carbohydrate part extends outside the cell to act as a cell-surface receptor for specific chemicals.

Question 17

What are glycoproteins?

Answer 17

Carbohydrate chains which extend from many extrinsic proteins on the outer surface of the cell membrane.

Question 18

What are the functions of glycoproteins?

Answer 18

• Act as recognition sites, specifically for hormones and neurotransmitters.
• Help cells attach to one another to form tissues.
• Allows cells to recognise each other.

Question 19

Which molecules can’t pass through the cell-surface membrane?

Answer 19

• Molecules which are insoluble in lipids.
• Molecules which are too large to diffuse through the membrane and too large to diffuse through the protein channels.
• Molecules which have the same charge as the protein molecules as they are repelled.
• Polar molecules due to the non-polar tails in the phospholipid bilayer.

Question 20

What is the fluid-mosaic model of the cell surface membrane?

Answer 20

The way in which all the various proteins combine into the structure of the cell-surface membrane.

Question 21

What does the “fluid” part of the fluid-mosaic model mean?

Answer 21

As the individual phospholipid molecules can move relative to one another, giving the membrane a flexible structure.

Question 22

What does the “mosaic” part of the fluid-mosaic model mean?

Answer 22

The proteins embedded in the phospholipid bilayer vary in shape, size and pattern.

Question 23

What are extrinsic proteins?

Answer 23

Proteins on the outside of the CSM

Question 24

What are intrinsic proteins?

Answer 24

Proteins inside the CSM.