Cell Membranes

Question 1

What does cholesterol do to the membrane?

Answer 1

Regulates fluidity + flexibility of membrane by packing phospholipids more tightly

Question 2

Why do phospholipids organise themselves into micelles and liposomes?

Answer 2

Keeps the head ‘wet’ and tails ‘dry’

Question 3

What is a micelle?

Answer 3

A monolayer of phospholipids (2-20nm)

Question 4

What is a liposome?

Answer 4

A bilayer (varying in size)

Question 5

What are proteins used for in the membrane?

Answer 5

Anagram - TRACIE

Transport = facilitated protein channels + active protein pumps
Receptors = peptide based hormones (insulin)
Anchorage = cytoskeleton attachments + extracellular matric
Cell recognition = antigens
Intracellular joinings = tight junctions + plasmodesmata
Enzymatic Activity = metabolic pathways (e.g. ETC)

Question 6

How are large molecules moved across membranes?

Answer 6

• Vesiculation (vesicle required)
  Endocytosis = movement in
  Exocytosis = movement out

Question 7

How are small molecules moved across membranes?

Answer 7

1. Simple Diffusion = gases + small uncharged polar molecules
2. Facilitated diffusion - passive transport = faster than simple + exhibits saturation kinetics.
   - Selective + susceptible to competition
3. Active transport - requires energy = uses carrier proteins against conc. gradients

Question 8

What are the two types of endocytosis?

Answer 8

• Pinocytosis: ‘cellular drinking’

- Phagocytosis: ‘cellular eating’

Question 9

What are the two types of exocytosis?

Answer 9

• Constitutive: continuous

- Regulated: triggered by receptors

Question 10

What are the 2 main families of Active Transport Proteins?

Answer 10

1. P Class Transporters (ion pumps)
   - Need a change in structure + shape to get across membranes (Phosphorylation = P)
2. ABC transporters
   - ‘ATP-Binding Cassettes’

Question 11

What do active transport proteins do, generally?

Answer 11

Use ATP hydrolysis to pump molecules across membranes