5.1 - Membrane Function & Structure

Question 1

Define compartmentalisation.

Answer 1

Formation of separate membrane-bound areas

Question 2

What occurs during compartmentalisation?

Answer 2

• Membranes separate contents of a cell from its environment
• Membranes separate organelles from one another

Question 3

Why is compartmentalisation important?

Answer 3

Metabolism in a cell includes different and incompatible reactions so different regions need to be split.

Question 4

State the components of a plasma membrane.

Answer 4

Phospholipid bilayer
Intrinsic proteins
Extrinsic proteins
Glycolipids
Glycoproteins
Cholesterol

Question 5

Describe the features of intrinsic proteins.

Answer 5

aka - integral, transmembrane proteins

• Embedded through both layers of the bilayer
• Have amino acids with hydrophobic R-groups on the external surface, this keeps them in place as the interact with the hydrophobic core of the membrane

Question 6

What are the 2 types of intrinsic proteins?

Answer 6

Channel proteins

Carrier proteins

Question 7

What are the features and functions of channel proteins?

Answer 7

• Hydrophilic channel allowing passive movement of polar molecules and ions down the concentration gradient
  - They would usually pass through the membrane very slowly as the centre of the bilayer is hydrophobic.
• Held in place by hydrophobic R-groups on the external surface of the protein interacting with the hydrophobic centre of the bilayer.

Question 8

What are the features and functions of carrier proteins?

Answer 8

Role in passive & active transport.

This involves the shape of the protein changing

Question 9

What is the structure of a glycoprotein?

Answer 9

• Embedded in cell surface proteins
• They are extrinsic proteins
• Consist of carbohydrate chains of varying lengths attached to proteins

Question 10

Describe the functions of glycoproteins.

Answer 10

• Cell adhesion - when cells join to form tight junctions in cell tissues
• Act as receptors for chemical signals - chemicals bind to receptors and causes a direct effect or series of events
• Cell signalling (communication)

Question 11

What is cell signalling?

Answer 11

• Neurotransmitter receptors at nerve cell synapses have neurotransmitters such as acetylcholine which bind and trigger an impulse in the next neurone
• Receptors for peptide hormones such as insulin and glucagon

Question 12

What are the features and functions of glycolipids?

Answer 12

• Lipids attached to carbohydrate chains
• Cell markers (antigens) recognised by the immune system as self (part of the organism) or non-self (not part of the organism), triggering an appropriate response.

E.g. antibody production

Question 13

What are the features and functions of extrinsic proteins?

Answer 13

• Peripheral proteins

- Hydrophilic R-groups on outer surfaces (to interact with the hydrophilic phosphate heads.

Question 14

What is the structure and function of cholesterol?

Answer 14

• Is an amphipathic (dual hydrophilic and hydrophobic ability) lipid
• Regulates membrane fluidity
• Positioned between phospholipid in the bilayer
• The hydrophilic end interacts with the phosphate ends and the hydrophobic ends interact with the fatty acid tails
• Stops phospholipids from getting too close and crystallising