Membrane Bilayers and Membrane Proteins

Question 1

Name the two main types of lipids

Answer 1

• Phospholipid

- Glycolipid

Question 2

Describe the structure and characteristics of a fatty acid

Answer 2

• Hydrocarbon chain of varying length
• Can be straight and saturated with single bonds (trans)
• Can be bent and non-saturated by presence of a double bond (cis)

Question 3

Why is a lipid amphipathic?

Answer 3

It has a hydrophilic head and a hydrophobic tail

Question 4

How are lipid bilayers formed?

Answer 4

• Lipid membrane is polar

- There is interaction between hydrophilic heads and hydrophobic tails

Question 5

What are the four types of motion that can occur in the lipid bilayer?

Answer 5

• Flexion
• Rotation
• Flip Flop
• Lateral Diffusion

Question 6

Name 3 functions of biological membranes

Answer 6

• Selectively permeable barrier
• Chemical environment control
• Communication
• Recognition
• Signal Generation
• Secretion
• Transport

Question 7

What is the most abundant component of membrane bilayers (dry weight)

Answer 7

Protein (60%)

Question 8

What influence do unsaturated fatty acids have on membrane fluidity?

Answer 8

The double bond creates greater room for movement between lipids and prevents crystallisation

Question 9

What are the 3 main elements of a cholesterol molecule?

Answer 9

• Polar Head
• Rigid Steroid Ring
• Non-Polar Hydrocarbon Tail

Question 10

Which part of the cholesterol molecule restricts movement?

Answer 10

Rigid Steroid ring

Question 11

Which part of the cholesterol molecule allows movement in the lipid bilayer?

Answer 11

Hydrocarbon tail

Question 12

How does the cholesterol molecule connect to phospholipids?

Answer 12

It forms a hydrogen bond

Question 13

What is the role of cholesterol in the lipid membrane?

Answer 13

• Stabilises the membrane

- Counteracts temperature changes

Question 14

Name 2 positions proteins are integrated into the membrane and what forces are they under?

Answer 14

Peripherally - bound to surface by electrostatic or hydrogen bonds
Integrally - interact with hydrophobic domains

Question 15

How are integral proteins are inserted into the membrane and what are they not removed by?

Answer 15

• Inserted by interacting with hydrophobic domains of lipid bilayer
• Cannot be removed by pH or ionic changes
• Only removed by detergents/solvents

Question 16

What is membrane asymmetry?

Answer 16

Opposite sides of the membrane have different compositions

Question 17

Give 3 pieces of evidence for the presence of membrane proteins

Answer 17

• Facilitated Diffusion
• Ion Gradients
• Freeze Fracture
• Cell Response Specificity

Question 18

Name the 3 ways membrane proteins associate with the lipid bilayer

Answer 18

• Peripheral
• Integral
• Transmembrane

Question 19

How can membrane proteins move?

Answer 19

• Conformational Change
• Rotational
• Lateral

Question 20

How do membrane proteins contribute to the cytoskeleton? Give an example of this

Answer 20

• Attachment proteins bind the cytoskeleton to the membrane

- Erythrocyte Cytoskeleton - Spectrin lattice joined end to end

Question 21

Name 3 mechanisms that restrict membrane protein mobility

Answer 21

• Lipid mediated effects
• Protein association
• Cytoskeleton association

Question 22

What ‘locks’ proteins into the membrane?

Answer 22

Hydrophobic nature of amino acid chain

Question 23

What makes proteins inside a eukaryotic cell?

Answer 23

• RNA

- Ribosomes

Question 24

What pauses protein synthesis and what restarts it?

Answer 24

• Signal Recognition Particle pauses protein synthesis

- Docking Protein restarts protein synthesis

Question 25

What is the role of a Docking Protein?

Answer 25

It brings the new protein and ER nearer the membrane so it can be fed through the bilayer

Question 26

What feeds the protein through the bilayer?

Answer 26

Signal Sequence Receptor

Question 27

How is the correct orientation of membrane proteins achieved?

Answer 27

Through membrane synthesis where the protein is directly inserted into the membrane and locked in by the hydrophobic amino acid chain