4.1 structure of the cell-surface membrane

Question 1

describe the (5) different substances of the cell-surface membrane.

Answer 1

• phospholipid bilayer: hydrophilic phosphate head & hydrophobic fatty-acid tail
• proteins (extrinsic, intrinsic, channels / carrier)
• glycolipids
• cholesterol
• glycoproteins

Question 2

describe the advantages of the phospholipid bilayer.

Answer 2

• allow lipid-soluble molecules to pass through
• prevent water-soluble substances to pass through
• flexible and self-sealing

Question 3

describe the uses of extrinsic & intrinsic proteins on the cell-surface membrane.

Answer 3

• extrinsic protein: on 1 side of bilayer only, acts as mechanical support or as cell receptors with glycolipids
• intrinsic protein: spans through both bilayer, acts as protein channels & carrier proteins

Question 4

describe the role of cholesterol in the cell-surface membrane.

Answer 4

• adds strength to membranes
• prevent leakage of water (very hydrophobic)
• makes membrane less fluid at high temperatures

Question 5

describe the role of glycolipids in the cell-surface membrane.

Answer 5

• acts as recognition sites
• maintain stability
• help cells to attach & form tissues

Question 6

explain what the fluid-mosaic model meant.

Answer 6

fluid: flexible phospholipid molecules could move relative to one another
mosaic: proteins embedded varies in shape, size and pattern

Question 7

what molecules doesn’t diffuse through the cell-surface membrane?

Answer 7

• insoluble in lipids
• large-sized
• polar / electrically charged