2. Cell Membrane Structure

Question 1

What is a glycolipid?

Answer 1

A lipid with a carbohydrate attached

Question 2

What is a glycoprotein?

Answer 2

A protein with a carbohydrate attached

Question 3

What are the components of a cell surface membrane? (5)

Answer 3

• proteins
• glycoproteins
• glycolipids
• cholesterol
• channel proteins

Question 4

What is a typical structure of a cell surface membrane called?

Answer 4

Fluid mosaic structure

Question 5

What does “fluid” in fluid mosaic structure refer to?

Answer 5

Phospholipids and proteins can move within the bilayer

Question 6

What does “mosaic” in fluid mosaic structure refer to?

Answer 6

Mixture of molecules (i.e. proteins and phospholipids) embedded in the membrane

Question 7

What happens to fatty acid tails when phospholipids are in water?

Answer 7

Hydrophobic: orientate themselves away from water (e.g. aqueous external environment and/or cytoplasm)

Question 8

What happens to glycerol and phosphate when phospholipids are in water?

Answer 8

Hydrophilic: orientate themselves towards the aqueous external environment and cytoplasm

Question 9

Structure of intrinsic proteins (including transmembrane proteins)

Answer 9

Often span the membrane.
Only made of protein.
Examples are channel and carrier proteins.

Question 10

Functions of intrinsic proteins

Answer 10

Provide structural support.
Channel proteins transport water-soluble substances across the membrane.
Carrier proteins allow active transport across the membrane.

Question 11

Structure of extrinsic/peripheral proteins

Answer 11

On the surface of the membrane. Some may have carbohydrates bound to them (glycoproteins)

Question 12

Function of extrinsic proteins

Answer 12

Gives mechanical support to the membrane.

Act as cell receptors for molecules (e.g. hormones) in conjunction with glycolipids.

Question 13

Structure of glycoproteins

Answer 13

Protein molecules with a carbohydrate attached to them (covalently bonded).
Hydrophilic.
Found on the surface of the phospholipid bilayer.

Question 14

Function of glycoproteins

Answer 14

Cell-surface receptors for hormones & neurotransmitters.
Helps cells to form tissues.
Recognition sites for cells (e.g. lymphocytes recognising an organism’s own cells)

Question 15

Structure of glycolipids

Answer 15

Carbohydrate covalently bonded with a lipid.
Carbohydrate extends from the phospholipid bilayer into the aqueous external environment: acts as a cell-surface receptor for chemicals

Question 16

Functions of glycolipids

Answer 16

Acts as a receptor
Maintains stability of the membrane
Helps cells attach to each other and forms tissues

Question 17

Structure of cholesterol

Answer 17

Fits in between phospholipids.

Very hydrophobic!

Question 18

Function of cholesterol

Answer 18

Adds strength to membrane - pulls together fatty acid tails of phospholipid molecules.
Reduces lateral movement of other molecules.
Regulates fluidity.
Prevents leakage of water and dissolved ions from the cell.