Cell Surface/plasma Membranes

Question 1

What is the cell surface membrane?

Answer 1

The cell surface membrane is the membrane which separates cells from their external environment

Question 2

How thick is the plasma membrane?

Answer 2

7-10nm

Question 3

What happens in the plasma membrane?

Answer 3

Site of chemical reactions

Site of cell communication (cell signalling)

The plasma membrane helps support the cell and maintain its shape

Question 4

How permeable are cell surface membranes?

Answer 4

Cell surface membranes are partially permeable

Question 5

What are phospholipid bilayers made of?

Answer 5

Hydrophilic Phosphate heads and Hydrophobic fatty acid tails

Question 6

What does hydrophilic mean?

Answer 6

Hydrophilic means water loving

Question 7

What does hydrophobic mean?

Answer 7

Hydrophobic means Water hating

Question 8

Features of phosphate heads:

Answer 8

Hydrophilic

Form the inner and outer layers of the membrane

Sandwiches the hydrophobic fatty acid tails

Question 9

Features of the fatty acid tails:

Answer 9

Hydrophobic

Uncharged and polar

Some tails consist of saturated fatty acids and some contain unsaturated fatty acids.

Question 10

What bond holds phosphate head to the fatty acid tail in a phospholipid bilayer?

Answer 10

Phosphoester bonds join the head to the tail

Question 11

What is a cholesterol and what are its roles?

Answer 11

Cholesterol is a type of lipid that is present in cell surface membranes.

It binds to the hydrophobic tails on phospholipids and causes them to pack more closely giving the membrane more stability.

Question 12

How does membrane permeability increase with temperature?

Answer 12

Permeability increases with temperature.

This is because the temp increases the kinetic energy within the phospholipid bilayer. This causes the membrane to lose its rigidity and become more fluid. This reduces the effectiveness of the membrane to polar molecules.

Question 13

What are intrinsic proteins?

Answer 13

They span the width of the membrane (embedded through layers)

They transport water soluble charged particles

Examples include: channel and carrier proteins

Question 14

What are extrinsic proteins?

Answer 14

A.K.A peripheral proteins

Can be present either side of bilayer

Some can move between layers

Normally have hydrophilic ‘R’ groups to interact with phospholipid heads.

Question 15

What are glycoproteins?

Answer 15

They are intrinsic proteins with a branching carb chain

They are involved in cell adhesion (cells joining together to form tissue)

They can also act as receptors for chemical signals eg. Hormones

Question 16

What are glycolipids?

Answer 16

Glycolipids are similar to glycoproteins

They are lipids with attached carb (sugar) chains

These molecules are called antigens and are recognised by cells of the immune system

They also stabilise the membrane by forming hydrogen bonds with surrounding water molecules

Question 17

Betalain test results:

Answer 17

The higher the temp the more betalain released. This is because the membrane of the beetroot cells become more permeable as the temp of the water increases.