Biochemistry - Cell Membranes

Question 1

Describe the plasma membranes of red blood cells

Answer 1

Sheet like structure between 60-100 Angstroms
Consists of mainly lipids + Proteins
very fluid
allows for diffusion of molecules

Question 2

What are fatty acids?

Answer 2

Building blocks of lipids (Possess hydrophobic properties)
Oleate is a 18 C Unsaturated chain
Palmitate is a 16 C Saturated chain

Question 3

What are phospholipids?

Answer 3

Phospholipid Comprised of: 2 FA’s, Glycerol, Phosphate + Alcohol
Simplest Phophatidate + Alcohol (Serine/Choline) forms a Phosphoglyceride
Sphignomyelein (Glycerol replaced by Sphingosine) form long unsaturated hydrocarbon chain
Bilayered sheets form (due to hydrophobic tails + hydrophilic heads)
Sheets are self assembled self sealing & Widespread & Close in on themselves

Question 4

What is cholesterol?

Answer 4

Contains 4 Hydrocarbon rings with a OH group on one end and a steroid group on other
Cholesterol sits parallel to phospholipid
Disrupts shape of reg. phospholipids + form complex with phospholipid which decreases fluidity

Question 5

What are the different types of membrane proteins

Answer 5

Integral proteins - span within layer intrinsic

Peripheral proteins - bind to surface of integral proteins & phospholipid head

Question 6

What are alpha spanning helices?

Answer 6

Bacteriarhodopsin that span inner part of membrane have non polar AAs

Question 7

What are Porins?

Answer 7

Consists of Beta pleated strands
Antiparallel arrangement
forms hydrogen bonds between chains)

Question 8

What is Prostaglandin H2 Synthase-1?

Answer 8

Held in the membrane by alpha helices within the membrane (has hydrophobic side chains)
Catalyses: Arachidonic acid Prostaglandin H2
Only detergents can remove protein (strongly bonded)

Question 9

Describe membrane spanning proteins

Answer 9

Membrane proteins may have alpha helices to span hydrophobic part, amino acids are found in this region and are non polar.
The more –ve the value of AA (free energy change), the more likely to be found in hydrophobic part
A hydropathy plot detects the hydrophobic parts of the protein in a 20 AA window. if free energy is plotted the highest hydropathy index = Hydrophobic part of protein.

Question 10

Describe the fluid mosaic model

Answer 10

Fluid (movement of phospholipid) mosaic (arrangement of proteins)
acts as a permeability barrier & solvent for intrinsic proteins

Question 11

Describe the diffusion of phospholipids

Answer 11

Lateral diffusion is fast and occurs from one face to same face
Transverse diffusion is slow and occurs one face to another (flip-flop)

Question 12

What affects membrane fluidity?

Answer 12

Affected by double bond + length of fatty acid
Double bond introduces kink so pack together less tightly
Cholesterol

Question 13

Whats the difference between gram negative and gram positive bacteria?

Answer 13

2 membranes = gram positive (gram staining shows which bacteria is present)
1 membrane = gram negative

Question 14

Describe cholesterol endocytosis

Answer 14

Cholesterol Is bound to LDL protein which eventually enters cell
LDL binds to receptor on CSM leads to Vesicle forming & being released from receptor.
Vesicle fuses with lysosome and breaks down LDL to release cholesterol
Process is reversed for neurotransmitters

Question 15

How can molecules be transported across membranes?

Answer 15

Facilitated diffusion/ Active transport/ Exchangers

Question 16

What is the role of P type Ca2+ ATPase?

Answer 16

Hydrolysis of ATP provides energy for the pump

Question 17

What are the 6 steps of P type Ca2+ ATPase function?

Answer 17

Binding of Ca2+
Phosphorylation of ATPase
Eversion of binding sites
Release of Ca2+ into lumen
Hydrolysis (of phosphaspartate)
Eversion (set to OG state)

P type ATPase (flippase) can also transport phospholipid from on side of the membrane to the other

Question 18

What are ATP binding cassette (ABC) transporters?

Answer 18

Called this as has 4 domains (2 bind to membrane, 2 bind to ATP)
Tumour cells less resistant to drugs (multi drug resistance)
Resistance is due to MDR protein which uses ATP and pumps drugs out of cell before they have an effect

Question 19

What does histidine permease do?

Answer 19

Transport histidine into cell

Question 20

What do secondary transporters do?

Answer 20

Use power of concentration gradient to power another

Can be antiport (sodium-calcium) or symport (sodium glucose)