Plasma Membrane

Question 1

Why is it called the fluid mosaic model?

Answer 1

• The phospholipids and proteins can move around via diffusion

• The many different types of proteins interspersed throughout the belayer move about within it

• The scattered pattern produced by the proteins within the phospholipid belayer looks somewhat like a mosaic when viewed from above

Question 2

Describe the structure of a phospholipid.

Answer 2

• Hydrophilic phosphate head

• Hydrophobic lipid tails

Question 3

What are the components of the hydrophilic phosphate head?

Answer 3

• Phosphate group

• Phosphoester bond

Question 4

What are the components of the hydrophobic lipid tails?

Answer 4

• Glycerol

• Ester bond

• Fatty acid

Question 5

What are the functions of cell surface membranes?

Answer 5

• Partially permeable barriers between the cell and its outside environment, between organelles and the cytoplasm and within organelles (compartmentalisation)

• Controls which substances enter and leave the cells

• Membranes allow recognition by other cells

• Sites of cell communication

Question 6

Describe the structure of the cell surface membrane.

Answer 6

The cell surface membrane is a belayer of phospholipids with embedded proteins in a fluid mosaic structure.

Question 7

What are the functions of membranes within cells?

Answer 7

• Compartmentalisation

• Can form vesicles to transport substances

• Allowing selected molecules to move in and out of the cell

• A site for biochemical reactions e.g. respiration

• Allowing a cell to change shape

• Provides attachment sites for enzymes

Question 8

What are intrinsic proteins?

Answer 8

Proteins that span the whole width of the membrane.

Question 9

What are extrinsic proteins?

Answer 9

Proteins that are confined to the inner or outer surface of the membrane.

Question 10

What are the roles of glycoproteins?

Answer 10

• Stabilising the membrane by forming hydrogen bonds with surrounding water molecules

• Sites where drugs, hormones and antibodies bind - cell recognition

• Act as receptors for cell signalling

• Cell adhesion

Question 11

What are glycoproteins?

Answer 11

Intrinsic proteins with an attached carbohydrate chain.

Question 12

What are glycolipids?

Answer 12

Lipids with an attached carbohydrate (sugar chain).

Question 13

What are the roles of glycolipids?

Answer 13

• Act as receptor molecules

• Act as cell markers

• Can be recognised by the cells of the immune system as self (cells of the organism) or non-self (cells from another organism)

Question 14

What are the roles of extrinsic proteins?

Answer 14

• Cell signalling

• Cell recognition

• Act as receptors for other molecules e.g. hormones

Question 15

What is the role of cholesterol?

Answer 15

• Increases the mechanical strength and stability of membranes

• Controls membrane fluidity (more = less fluid)

Question 16

What are the factors that affect fluidity?

Answer 16

• Length of the fatty acid side chains (longer = lower fluidity)

• Proportion of fatty acids which are saturated (higher proportion of saturated fats = lower fluidity)

• Cholesterol content (higher = lower fluidity)

Question 17

Describe the process of cell signalling.

Answer 17

• One cell releases a messenger molecule

• This molecule travels to another target cell

• This messenger molecule binds to a membrane bound receptor with a complementary shape on the cell surface membrane of the target cell

• A response is triggered