4.1 Structure of the cell-surface membrane

Question 1

What is made up of a cell membrane?

Answer 1

1. phospholipid
2. glycolipids
3. protein
4. glycoprotein
5. channel protein
6. cholesterol

Question 2

How is the structure of a phospholipid?

Answer 2

1.hydrophilic phosphate head
2. hydrophobic fatty acid tails

Question 3

Does the hydrophilic phosphate head point inwards or outwards?

Answer 3

Outwards

Question 4

Does the hydrophobic hydrocarbon tails point inwards or outwards?

Answer 4

Inwards

Question 5

how are the phospholipids arranged in a cell membrane?

Answer 5

Bilayer

Question 6

What is the function of phospholipids?

Answer 6

1. allow lipid-soluble substances to enter or leave the cell
2. prevent water-soluble substances to enter or leave the cell
3. make the membrane flexible and self-sealing

Question 7

What are the two places that proteins are located?

Answer 7

1. in the surface of the bilayer
2. completely span (跨越) the bilayer

Question 8

What is channel protein?

Answer 8

Channels that form water-filled tubes to allow water-soluble ions to diffuse and span (跨越) across the membrane.

Question 9

What is carrier protein?

Answer 9

Proteins that bind to ions or molecules like glucose and amino acids, then change shape in order to move these molecules across the membrane.

Question 10

What are the functions of protein?

Answer 10

1. provide structural support
2. as a channel transporting water-soluble substances across the membrane
3. allow active transport across the membrane through carrier proteins
4. form cell-surface receptors for identifying cells
5. help cells adhere together (黏在一起)
6. acts as receptors

Question 11

Where is cholesterol located?

Answer 11

Within the phospholipid bilayer

Question 12

Are cholesterol hydrophobic or hydrophilic?

Answer 12

Hydrophobic

Question 13

Why does cholesterol bind with fatty acid tails and pull them together?

Answer 13

To limit fatty acid tails’ movement without making the whole membrane rigid (死板) .

Question 14

What are the functions of cholesterol?

Answer 14

1. add strength to the membrane
2. reduce lateral (橫向) movement of molecules
3. make the membrane less fluid at high temperature
4. prevent loss of water and dissolved ions

Question 15

What are glycolipids?

Answer 15

Carbohydrate chains that are attached to the hydrophilic phosphate head from the phospholipid bilayer on the outer surface of membrane.

Question 16

What are glycolipids made up?

Answer 16

Covalent bond between lipid and carbohydrate.

Question 17

How do glycolipids act as a receptor for special chemicals?

Answer 17

The carbohydrate extends from the phospholipid bilayer into the watery environment outside the cell.

Question 18

What are the functions of glycolipids?

Answer 18

1. act as recognition sites
2. help maintain the stability of membrane
3. help cells to attach to each other to form tissues

Question 19

What are glycoproteins?

Answer 19

Carbohydrate chains that are attached to the extrinsic (外在的) protein on the outer surface of membrane.

Question 20

What are glycoproteins made up?

Answer 20

Covalent bond between protein and carbohydrate.

Question 21

What are the functions of glycoproteins?

Answer 21

1. acts as recognition sites
2. helps cells to attach to each other to form tissues
3. allow cells to recognise each other
4. acts as receptors for hormones and neurotransmitters

Question 22

What is the model that shows the structure of a cell membrane?

Answer 22

Fluid-mosaic model

Question 23

Why is the model called ‘fluid-mosaic’ model?

Answer 23

1. ‘fluid’ because individual phospholipids can move relatively to one other
2. ‘mosaic’ because proteins that are embedded in the phospholipid bilayer vary in shape and size