module 2 lectures 3+4

Question 1

Passive transport - GLUT1

Answer 1

Glucose transporter in erythrocytes
Implicated in diabetes
Facilitated diffusion: 50,000x faster than uncatalyzed
Passive transport: [glucose] cannot be higher than surrounding medium
Transport process can be described like enzyme reaction

Question 2

Electroneutral co-transport: chloride-bicarbonate exchanger

Answer 2

CO2 transporter in erythrocytes
- Increases transport rate >1Mx
- 14 TM helices
- Antiporter: Cl-, HCO3-

Question 3

Active transport

Answer 3

Requires energy

From chemical reaction: primary active transport
- ATP-driven ion transport in reverse makes ATP
From coupled transport: secondary active transport
- Ion gradients from primary transport provide the energy for secondary transport
- These ion gradients essential: ionophores (vancomycin) collapse them and kill cells

Question 4

V-class proton pumps

Answer 4

vacuolar membranes in plants, yeast + fungi
endosomal and lysosomal membranes
ATP hydrolysis

Question 5

F-class proton pumps

Answer 5

bacterial
inner mitochondrial membrane
ATP synthesis

Question 6

P-class pumps

Answer 6

ATP hydrolysis
plasma membrane of plants and fungi
e.g. Na/K pumps

Question 7

ABC superfamily

Answer 7

bacterial plasma membranes
ATP hydrolysis

Question 8

P-type ATPases

Answer 8

cation transporters
phosphorylated on Asp

antiporter = 3Na+ / 2K+
create v= 50-70mV

Question 9

F and V-type ATPases

Answer 9

Proton transport driven by ATP hydrolysis
V-type structurally related (Vo, V1)
Acidify intracellular compartments

Question 10

ABC (ATP binding cassette) transporters

Answer 10

Pump amino acids, peptides, proteins, metal ions, lipids, compounds (drugs)

MDR1: multi-drug transporter
- Resistance of tumors to drugs

CFTR: Cl- channel
- Defective transport makes mucus thick: bacteria grow

Question 11

Secondary transport: lactose permease

Answer 11

H+/lactose co-transporter (E. coli)
Lactose goes in the cell
12 TM helices
Protonatable Glu, Arg side chains
Major facilitator superfamily

Question 12

Ion channels

Answer 12

Differ from transporters
- Flux ~ unrestrictive diffusion > transporters
- Ligand- or voltage gated

Open only for ms
- Cannot be monitored biochemically
- Instead monitored electrically – patch-clamp (monitoring one-few channels)

Question 13

Ion channels

Answer 13

Differ from transporters
- Flux ~ unrestrictive diffusion > transporters
- Ligand- or voltage gated

Open only for ms
- Cannot be monitored biochemically
- Instead monitored electrically – patch-clamp (monitoring one-few channels)

Question 14

Bacterial K+ channel

Answer 14

• K+ passes 10,000x more readily than Na+
• 4 subunits, 2 TM helices each
• Carbonyls coordinate K+ - replace waters

Question 15

Voltage- and ligand-gated channels in neurons

Answer 15

Muscle contraction
- Action potential in the motor neuron opens voltage-gated Ca2+ channel and releases acetylcholine
- Acetlylcholine opens nicotinic acetylcholine receptor (ligand-gated channel)
- - Acetylcholine transient ligand
- - Na+/K+ antiporter
- - Associated with learning and memory and disorders (schizophrenia, epilepsy, drug (e.g. nicotine) addiction, Alzheimer’s)
- Depolarization of membrane leads to opening of voltage-gated Na+ channel and generation of action potential
- Ca2+ channels release Ca2+ from sarcoplasmic reticulum
- Same family as GABA and Gly receptors (Cl- and HCO3- channels) and serotonin receptor (cation channels)

Question 16

Consequences of defective ion channels

Answer 16

• Voltage gated Na+ channel: muscle paralysis/stiffness
• Cystic fibrosis
• Toxins target ion channels