Chapter 9

Question 1

What are the 6 functions of biological membranes?

Answer 1

1. Separate cells from external medium and intracellular compartments
2. Facilitate transport of substrates and ions in the cell
3. Membranes for mitochondria, chloroplasts and plasma membrane of bacteria are sites of energy conversion
4. Neural signal transduction
5. Involved in cell-cell interaction
6. Membranes contain receptors for hormones and other signals

Question 2

What are the 3 forms of membrane?

Answer 2

Micelle- where individual units are wedge-shaped (big circle) (fatty acids and detergents)
Bilayer- individual units are cylindrical (flat stacks) (glycerophospholipids and sphingolipids)
Liposome- bilayer wrapped in a circle like micelle

Pictures on slide 3

Question 3

Why are liposomes more useful than bilayers?

Answer 3

They have no exposed hydrocarbon tails so they are more stable and energetically favourable

Question 4

What is a peripheral protein and an integral protein (single transmembrane helix and multiple trans membrane helix)?

Answer 4

Peripheral protein- attaches to outside membrane wall or other proteins in membrane using lipid anchors (inside or outside cell)
Integral protein- embedded into the membrane and can be detached using detergents
Single helix- has just one row embedded into membrane
Multiple helix- has multiple rows embedded into helix

Diagram on slide 5

Question 5

What are the two types of lipid diffusion across membranes and what is the relative time to complete each?

Answer 5

1. Uncatalyzed transverse (flip flop) diffusion- lipid molecule flips sides of the membrane
   T1/2 is in days length
2. Transverse diffusion catalyze by flippase- flippase embeds in the membrane and the lipid uses it to flip to the other side of membrane
   T1/2 is in seconds length

Question 6

What are the two ways acyl groups are ordered in the lipid bilayer interior?
What changes these states from one to the other?

Answer 6

Paracrystalline state (gel)- ordered state below phase transition temperature
Fluid state- at temperatures well above phase transition, the hydrocarbon chains are disordered and membrane is fluid
Heat changes paracrystalline state to fluid state

Question 7

What state is the lipid membrane in at intermediate temperatures?

Answer 7

Liquid-ordered state (between paracrystalline state and fluid state)
Hydrocarbon chains are partially ordered, but lateral diffusion is possible

Question 8

How is the percentage of total fatty acids affected by temperature for saturated and unsaturated?

Answer 8

Saturated- As temperature goes up, more fatty acids are needed and used
Unsaturated- as temperature goes up, less fatty acids are needed

Question 9

How does the percentage of total fatty acids change as you get more carbons?
More double bonds?

Answer 9

More carbons - higher fatty acid percentage

More double bonds- higher fatty acids percentage

Question 10

How do sphingolipids create lipid tarts in biological membranes?

Answer 10

Sphingolipids associate with cholesterol to form lipid rafts that are domains of liquid ordered lipid surrounded by largely disordered fluid phospholipid

Picture on slide 9

Question 11

How are lipid rafts stabilized?

Answer 11

Interactions between the cholesterol ring and long saturated hydrocarbon tails of sphingolipids

Question 12

What are lipid rafts?

Answer 12

Attachment points for peripheral membrane proteins that are anchored to the membrane by two covalently attached saturated acyl chains or glycosylated phosphoinositol derivatives (GPI)

Question 13

What are the 3 types of covalent attachment inside the cell?

Answer 13

1. Using palmitoyl group on internal Cys or Ser
2. Using N-Myristoyl group on amino-terminal Gly (amide bond)
3. Using farnesyl group on carboxyl-terminal Cys

Picture on slide 11

Question 14

What is the one type of covalent attachment outside the cell?

Answer 14

Using GPI anchor on carbonyl terminus

Picture on slide 11

Question 15

How do you know if a protein is bonded outside the cell or inside the cell based on what it’s bonded to?

Answer 15

Proteins anchored by Glycosylated phosphoinositol (GPI) are always outside the cell
Proteins anchored by fatty acyl or prenyl chains are always inside the cell

Question 16

How are amino acids distributed (inside or outside the cell) in integral membrane proteins?

Answer 16

Charged residues (Asp, Glu, Arg, Ltd) are locates mostly outside the membrane with some exceptions for interactions
Resides with apolar side chains dominate inside the hydrophobic slab of the bilayer
Tryptophan and tyrosine are inbetween the hydrocarbon chain and polar headgroup

Question 17

What are the two archetypes of membrane transport protein structure?

Answer 17

α-helices- coiled up tightly knit through the membrane
β-barrel- membrane spanning strands

Pictures on slide 13

Question 18

How are carbonyl and amide groups of the protein backbone inside the bilayer bonded? Why?

Answer 18

That are bonded with hydrogen bonds so that the transfer of uncompensated electric dipoles on the protein backbone into the apolar core of bilayer won’t have a high energy penalty

All peptide groups inside bilayer cores are hydrogen bonded in secondary regular structures

Question 19

What are the 8 biological processes the membrane fusion is a result of?

Answer 19

1. Budding of vesicles from golgi complex
2. Exocytosis
3. Endocytosis
4. Fusion of endosome and lysosome
5. Viral infection
6. Fusion of sperm and egg
7. Fusion of small vacuoles
8. Separation of two plasma membranes at cell division

Question 20

How does membrane fusion play a role in neural transmission?

Answer 20

Neurotransmitter release in neural synapses involves fusion of membrane vesicles loaded with neurotransmitter with plasma membrane. Requires SNAP and SNARE proteins

Diagram on slide 16 and 17

Question 21

How does concentration gradient drive diffusion across the membrane?
(Equation)

Answer 21

ΔG=2.3RT*log[C2]/[C1]
R=8.32 J/molK

Concentration will always move to the side with less (always find equilibrium m)

Question 22

How does electric potential drive diffusion across the membrane?
(Equation)

Answer 22

ΔG=-mFΔΨ
F= 96480 J/Vmol
ΔΨ= electric potential difference between two compartments

Question 23

What is the entire equation that connects the concentration gradient and electric potential for finding diffusion across a membrane?
What is the equation for protons?

Answer 23

ΔG=-mFΔΨ+2.3RT*[Cin][Cout]

For protons:
ΔG=-FΔΨ+2.3RT*ΔpH(out-in)

Question 24

What are the 6 types of membrane transport?

Answer 24

1. Simple Diffusion (nonpolar only) Sout->Sin (down conc gradient)
2. Facilitated Diffusion- Sout->Sin with help of embedded protein (down electrochemical gradient)
3. Primary Active Transport- uses ATP (against electrochemical gradient)
4. Secondary active transport- driven by ion moving down its gradient (electrochemical gradient)
5. Ion channel- may be gated by a ligand or ion
   (Down electrochemical gradient)
6. Ionophoremediated ion transport- ion bonded to ionophore goes through membrane (down electrochemical gradient)
   Slide 20

Question 25

What are primary active transporters?

Answer 25

Couple endergonic transport of X against its electrochemical gradient (ΔG>0) to an exergonic chemical reaction (ΔG<0)

Question 26

What are secondary active transporters?

Answer 26

Couple endergonic transport of X against X electrochemical gradient (ΔG>0) to exergonic transport of Y down Y electrochemical gradient (ΔG<0)

Question 27

What are passive transporters?

Answer 27

Can only transport X down it’s electrochemical gradient (ΔG<0)