Cell Surface Membrane

Question 1

Explain the structure of the cell-surface membrane.

Answer 1

• Fluid structure is given from constantly moving phospholipid molecules.
• Protein molecules unevenly distributed throughout the membrane like a mosaic.

Question 2

Explain how the cell membrane controls the entry & exit of the cell.

Answer 2

• Structure of the bilayer enables lipid soluble molecules to pass through cell membrane quickly but restricts passage of water soluble ions and polar molecules.
• Very small molecules such as water, CO2 and O2 can pass through the gaps between phospholipids. These molecules are neutral or slightly charged.

Question 3

What do proteins do in the cell-surface membrane?

Answer 3

-Protein molecules act as carrier or channels and aid the passage of water soluble ions and polar molecules across the membrane. They can also contain enzymes.

Question 4

What do carrier proteins do? Why are they specialised for this?

Answer 4

-Carrier proteins have a specific tertiary structure complimentary to polar molecules, aiding their transport by facilitated diffusion and active transport.

Question 5

What do channel proteins do? Why are they specialised?

Answer 5

-Channel proteins also have a specific tertiary structures and decide which molecules can be transported via facilitated diffusion.

Question 6

What can protein molecules also be used for? How are they specified?

Answer 6

-Other protein molecules act as receptors for hormones so the cell can respond, e.g. insulin which attaches to the membrane. Share a specific tertiary structure and AS for a specific hormone.

Question 7

What role do glycolipids have in the cell-surface membrane?

Answer 7

Carbohydrate joined with a lipid, acts as a recognition site, e.g. cholera toxins

Question 8

What role do glycoproteins have?

Answer 8

Branched carbohydrate joined with a protein, acts as a recognition site for chemicals, e.g hormones.

Question 9

What role does cholesterol have in the cell surface membrane?

Answer 9

Adds strength to the membrane and prevents movement of other molecules in the membrane.

Question 10

What does microvilli do?

Answer 10

• Increase SA and are numerous on cells specialised for absorption
• Improved efficiency of digestion in the gut as certain enzymes are attached to their surface.
• Seen with light microscope as a fringe on top of cell called brush border.