membrane structure and function

Question 1

common features of a membrane

Answer 1

Non covalent assemblies (held by a lot of weak forces)

Asymmetric 

Specific proteins that carry out distinctive functions 

Fluid 

Two molecules thick: closed boundaries 

Electrically polarized

Question 2

lipid composition

Answer 2

Hydrophobic tail

Hydrophilic head 

Phospholipids and glycolipids are amphipathic (have both hydrophobic and hydrophilic ends) 

Readily form a bilayer in aqueous media 

Form lipid bilayer (liposomes) 

Have clinical uses such as delivering drugs

Question 3

Effects of high temperature on the fluidity of membrane

Answer 3

Increases fluidity

The fatty acid tails of the phospholipid becomes less rigid 

Also makes the membrane more fluid

Question 4

Effects of low temperature on the fluidity of membrane

Answer 4

Fluidity decreases

Question 5

Effects of cholesterol on the fluidity of membrane

Answer 5

Cholesterol molecules slip in between the phospholipids

At low temperature, cholesterol cause fluidity to increase because the cholesterol   therefore fluidity decreases 

At high temperatures, cholesterol will cause phospholipids to come in closer and bond with the cholesterol and phospholipid making the membrane more rigid 

In spur cell anaemia, the cholesterol content increases by 25-65% causing the RBC to look abnormal

Question 6

Effects of chain length on the fluidity of membrane

Answer 6

Increased length increases rigidity as there are more bonds

Therefore less fluid

Question 7

Effects of degree and extent of saturation on the fluidity of membrane

Answer 7

The more saturated, the more rigid

Unsaturated chains contain a double bond which causes a kink in the chain, which decreases the interactions between the chains and increases fluidity 

Straight chains have more interactions between chains therefore less fluid

Question 8

Which orientation of movement is ideal for phospholipids?

Answer 8

Lateral movement is more rapid compared to transverse. Transverse movement is slow and requires enzymes

Question 9

Membrane synthesis lipids

Answer 9

Phospholipids are manufactured on the cytosolic surface of the ER and enzymes deposit these phospholipids on the cytosolic side of the bilayer

Scramblases remove randomly phospholipid from one half of the lipid bilayer and insert it in the other half 

This ensures the phospholipid are evenly distributed between each monolayer 

Floppase moves phospholipids from the extracellular side to the cytosolic side 

These enzymes maintain the asymmetric arrangement of the bilayer

Question 10

what happens to the contents of the cell during apoptosis?

Answer 10

They aren’t released

Question 11

Does apoptosis stimulate any response?

Answer 11

No apoptosis doesn’t stimulate any response including inflammation

Question 12

What does the cell undergoing apoptosis release on its membrane and what enzymes does that activate/inactivate?

Answer 12

• Phosphatidylserine on outside of cell: “Eat me signal” Caspases enzymes inactivate Flippase and activate the scramblase by cleavage

Question 13

Integral membrane protein

Answer 13

Transmembrane region is often an alpha helix and is usually hydrophobic

Strong non covalent bonds  

Can pass through membrane single or multiple times 

Protein is interlinked with membrane so very difficult to extract

Question 14

Peripheral membrane protein

Answer 14

Located on the extracellular side

Associated by non covalent bonds 

Loosely associated with membrane therefore easier to extract 

Can be associated with lipids or proteins

Question 15

Lipid anchored membrane proteins

Answer 15

Covalently linked to a lipid molecule

Question 16

Membrane carbohydrates

Answer 16

Form 2-10% of membrane weight

Face away from the cytosol 

Involved in cell-cell interactions or cellular recognition 

In red blood cells 8% of weight is carbohydrate  

Blood group determined by the polysaccharides attached to red blood cells