Cell Membranes

Question 1

What is the fluid mosaic model?

Answer 1

The model that shows how proteins and lipids are arranged in cell membranes.
It is fluid as components of membrane move in relation to each other
Mosaic due to the protein components in bilayer.

Question 2

What is the width of the cell membrane?

Answer 2

7-8nm

Question 3

What is an intrinsic protein?

Answer 3

Protein molecules spanning the phospholipid bilayer of the plasma membrane

Question 4

Intrinsic protein functions are:

Answer 4

Transport proteins which transport water soluble molecules and ions in/out of cell.
Hydrophobic portion on outside, hydrophilic portion forms channel on inside of protein.
Can be enzymes

Question 5

What is an extrinsic protein?

Answer 5

Protein molecules attached to surface of plasma membrane, can float or be fixed.
Can provide mechanical support.

Question 6

What are the general functions of membrane?

Answer 6

1. Selectively permeable (controls movement of ions/molecules in/out
2. Absorption of nutrients
3. Secretion of chemicals
4. Forms boundary around cell -retains contents, internal boundary between organelles and cytoplasm (compartmentalisation)
5. Isolates digestive enzymes
6. RER - attachment of ribosomes
7. SER - Golgi body

Question 7

What is a glycoprotein?

Answer 7

Protein with carbohydrates attached to it (e.g. glycocalyx)

Question 8

What are glycoprotein functions?

Answer 8

1. Stabilising membrane, carb section forms hydrogen bonds with water
2. Receptor: carb chain can bind with chemicals that signals cell to respond. E.g. insulin binds to receptors on membrane of liver cells to signal to absorb glucose, drugs may block receptors
3. Cell recognition: some act as self recognition sites, which indicates they belong to organism, stopping WBC attack
4. Anti gen, if cells enter body of another organism, WBC attacks

Question 9

What is a glycolipid?

Answer 9

Lipid with carbs attached to it.

Question 10

Function of glycolipid?

Answer 10

Carbs chain extends to watery environment outside and stabilises membrane.
Acts as recognition site

Question 11

What is the phospholipid component?

Answer 11

Makes up most of plasma membrane
Forms phospholipid bilayer
Hydrophilic head faces outwards, attracted to water surrounding cell.
Hydrophobic tail faces inwards, repelled by water
Small non polar molecules pass through bilayer via simple diffusion.

Question 12

What is cholesterol?

Answer 12

A lipid soluble molecule that can combine with other lipids.
It’s a steroid
Forms between phospholipid molecules

Question 13

Function of cholesterol?

Answer 13

Makes membrane more stable as pulls phospholipid tails together making it less fluid.
Very hydrophobic to prevent leakage of water and ions.

Question 14

How does heat effect membranes

Answer 14

When temp increases, phospholipid molecules that make membrane so increase in kinetic energy and move faster, size of gaps in membrane increases
So the membrane becomes more fluid and more permeable.
Also proteins denature