2.1.5 Biological membranes - Phospholipid bilayer

Question 1

Define plasma membrane

Answer 1

The cell surface membrane with separates the cell from its external environment.

Question 2

From what are membranes formed?

Answer 2

From a phospholipid bilayer

Question 3

What is the structure of a phospholipid bilayer?

Answer 3

the fatty acid tails are hydrophobic (and non-polar) therefore they face inwards. the phosphate heads are hydrophilic (and polar) therefore they face outwards. this causes the phosphate heads to sandwich the fatty acid tails in the middle.

Question 4

Why is the phospholipid bilayer perfectly suited as membranes?

Answer 4

since the outer surfaces of the hydrophilic phosphate heads can interact with water.

Question 5

Why is the model known as the fluid mosaic model?

Answer 5

The fluid part because the phospholipids can move relative to each other. And mosaic because there are proteins embedded in the bilayer.

Question 6

What are the features of a cell-surface membrane?

Answer 6

• phospholipids
• cholesterol
• intrinsic proteins OR extrinsic proteins
• glycoproteins
• glycolipids

Question 7

Channel proteins -

Answer 7

• embedded in phospholipid bilayer
• provides a hydrophilic channel which allows the passive movement of polar molecules or ions down a concentration gradient through a membrane.

Question 8

Carrier proteins -

Answer 8

• embedded in cell-surface membrane
• permits facilitated diffusion
• play an important role in transporting substances across the membrane down the concentration gradient

Question 9

Glycoproteins -

Answer 9

• made out of proteins
• intrinsic proteins, embedded in cell surface membrane
• attached are sugar chains
• FUNCTION: help cell adhesion and as receptors for chemical signals

Question 10

Glycolipids -

Answer 10

• made out of lipids
• similar to glycoproteins
• they have attached a sugar chain (carbohydrate)
• they are cell markers or antigens

Question 11

Extrinsic proteins -

Answer 11

• present on side of the bilayer
• normally have hydrophilic R-groups on their outer surfaces and interact with the polar heads of the phospholipids or with intrinsic proteins.

Question 12

Cholesterol -

Answer 12

• lipid that has a hydrophilic end and a hydrophobic end

- FUNCTION: regulate fluidity of membranes and to add stability to membranes.