2. Cell Membranes

Question 1

What are 2 functions of the cell-surface membrane?

Answer 1

• It allows different conditions to be established inside and outside of a cell
• It controls the movement of substances in and out of the cell

Question 2

Describe the position of the phospholipids in the phospholipid bilayer:

Answer 2

The hydrophilic heads of both layers point to the outside of the cell surface membrane, while the hydrophobic tails point inwards.

Question 3

What are the 3 functions of the phospholipids in the membrane?

Answer 3

• Allow lipid soluble substances to enter and leave the cell
• Prevent water soluble substances entering and leaving the cell
• Make the membrane flexible and self-sealing

Question 4

Where are proteins found in the cell membrane?

Answer 4

They are interspersed throughout the cell surface membrane. They are also embedded into the phospholipid bilayer.

Question 5

What are the two main ways that proteins are embedded into the phospholipid bilayer?

Answer 5

1. Some proteins occur in the surface of the bilayer and never extend completely across it
2. Other proteins completely span the phospholipid bilayer from one side to the other

Question 6

What is the purpose of the proteins that just occur in the surface of the bilayer?

Answer 6

They act either to give mechanical support, or in conjunction with glycolipids, as cell receptors for molecules such as hormones.

Question 7

What is the purpose of the proteins that span the entirety of the bilayer?

Answer 7

Some are protein channels, which form water-filled tubes to allow water-soluble ions to diffuse across the membrane.

Question 8

Where are cholesterol molecules found in the cell-surface membrane?

Answer 8

Within the phospholipid bilayer

Question 9

Give 3 functions of cholesterol in the membrane:

Answer 9

• Reduce lateral movement of other molecules including phospholipids
• Make the membrane less fluid at high temperatures
• Prevent leakage of water and dissolved ions from the cell

Question 10

Why do cholesterol molecules prevent leakage of water and dissolved ions?

Answer 10

There are very hydrophobic.

Question 11

What are glycolipids made up of?

Answer 11

A carbohydrate covalently bonded with a lipid.

Question 12

What are 3 functions of glycolipids in cell-surface membranes:

Answer 12

• Act as recognitions sites
• Help maintain the stability of the membrane
• Help cells to attach to one another and so form tissues