What is a membrane?

Question 1

Describe the structure of the cell membrane.

Answer 1

• Composed of phospholipids
• Has glycerol back bone
• Hydrophilic head attached to phosphate
• Hydrophobic fatty acid tail
• Amphipathic
• Fluid structure

Question 2

At what level of water concentrations do phospholipids form a monolayer?

Answer 2

Low water concentrations.

Question 3

At what level of water concentrations do phospholipids form a bilayer?

Answer 3

High water concentrations.

Question 4

What does the length of the fatty acid side chains determine?

Answer 4

The thickness of the bilayer.

Question 5

What does the nature of the head groups on phospholipids determine?

Answer 5

How densely packed the phospholipids are

Question 6

How does binding of cholesterol affect the membrane?

Answer 6

Stiffens the membrane (reduces fluidity).

Question 7

What is the membrane permeable and impermeable to?

Answer 7

It is permeable to small uncharged polar molecules e.g. O2, CO2, NH3, water

It is impermeable to water-soluble substances e.g. ions, proteins, sugars.

Question 8

Describe peripheral proteins.

Answer 8

• not embedded in membrane

- adhere tightly to surfaces of membrane

Question 9

Describe integral proteins.

Answer 9

• embedded in membrane and can also span all the across it.
• can be attached to fatty-acid derivatives
• Involved in intracellular signalling
• involved in transport.

Question 10

Give examples of integral membrane proteins.

Answer 10

• ligand-binding receptors
• adhesion molecules (e.g. integrins)
• pores and channels
• pumps
• carriers
• enzymes
• docking-marker acceptors for exocytosis

Question 11

Describe membrane carbohydrates.

Answer 11

• Short carbohydrate chains on exterior of membrane
• work with glycoproteins and glycolipids to form the glycocalyx
• act as self-identity markers
• make sure cells don’t overgrow their own territory.