3.a. The fluid-mosaic model of plasma membranes

Question 1

What are the two substances that membranes are made up of?

Answer 1

• Proteins

- Phospholipids

Question 2

Phospholipids form bilayers. What does this mean?

Answer 2

One sheet of phospholipid molecules are opposite another

Question 3

Describe the positioning of the phospholipid on the inner layer of the membrane (2)

Answer 3

• Hydrophilic heads point in

- Towards cytoplasm (interacts with water there)

Question 4

Describe the positioning of the phospholipid layer on the inner layer of the membrane

Answer 4

• Hydrophilic heads point out

- Interact with water surrounding cell

Question 5

In what direction do the hydrophobic tails point?

Answer 5

Towards each other

Question 6

What are the two types of protein in a membrane?

Answer 6

Extrinsic and intrinsic proteins

Question 7

What are the three roles of an extrinsic protein?

Answer 7

• To give structural support
• To form recognition sites (by identifying cells)
• Receptor sites for hormone attachment

Question 8

What are the two roles of an intrinsic protein?

Answer 8

• Channel protein (to move ions by active transport)

- Carrier protein (to allow water-soluble substances across)

Question 9

How is the membrane like a fluid-mosaic model?

Answer 9

Fluid=Phospholipid molecules can move within a layer

Mosaic= Proteins embedded in bilayer vary in shape, size, and pattern

Question 10

What other substances does a membrane contain and where are they found?

Answer 10

• Cholesterol, animal cell membranes

- Glycoproteins and glycolipids, outer layer of membrane

Question 11

What is the carbohydrate layer around the membrane called?

Answer 11

Glycoalyx

Question 12

What are the roles of cholesterol and glycoproteins in the cell membrane?

Answer 12

• Cholesterol= makes the membrane more rigid/stable

- Glycoproteins= some molecules in the glycoalyx are hormone receptors