Unit 5

Question 1

ATP powered pumps

Answer 1

• Couples hydrolysis of ATP to transport of a molecule against its conc. gradient

Question 2

Channel proteins (ions)

Answer 2

• Transport ions down conc. gradient through hydrophillic pore in emmbrane protein. Can exist in an open or closed conformation & when open many ions can pass simultaneously

Question 3

Carrier Proteins (transporters)

Answer 3

• Bind water-soluble molecule on one side of the membrane & deliver them to the other side. involves a conformational change in the protein. Only bind over a few molecules at a time

Question 4

Uniports

Answer 4

• Work in passive diffusion & are selected for one type of molecule. They move molecules down their conc. gradients
• High rate of substance movement
• Partition coeffecient irrelevant
• No contact with hydrophobic lipid environment
• Limited by # of uniporters in membrane
• Specific transport

Question 5

GLUT1

Answer 5

• Main unporter for glucose in erythrocytes

Question 6

Symporter / Antiporter

Answer 6

• Use an existing electrochemical gradient rather than ATP hydrolysis to move 1 of the molecules against its conc. gradient & a second molecule down its gradient
• Secondary active transport
• Conformational change necessary to deliver the 2 molecules to other side of membrane only happens when both are bound to transporter

Question 7

P-class ATP powered pumps

Answer 7

• Heterotetramer with 2 subunits α α & β
• β phosphorylated during transport

Question 8

V-class ATP powered pumps

Answer 8

• Multiple subunits
• transports only protons against their gradient
• acidifies lysosome & vacuole

Question 9

F-class ATP powered pumps

Answer 9

• Multiple subunits
• related to V-class
• only member that generates ATP
• pumps only protons
• found in inner membrane of mitochondria, thylakoid, bacterial plasma membrane

Question 10

ABC superfamily

Answer 10

• More members than other classes
• Transport sugars, amino acids, phospholipids, proteins
• Responsible for multidrug resistance

Question 11

K+ / H+ ATPase

Answer 11

• Pareital cells of stomach
• Produces acidic environment
• Target of drugs like Prilosec, Nexium, Prevacid
• Acidity can also be centralised by basic anions found in over-the-counter medications

Question 12

Na+ / K+ ATPase

Answer 12

• Inhibited by the poison ouabain. By altering Na+ gradient, it indirectly affects Na+ / Ca2+ exchanger pumping Ca2+ out of cells, causing increased intracellular Ca2+. Affects heart contractions

Question 13

CFTR

Answer 13

• Cystic Fibrosis Transmembrane conductance Regulator
• Member of ABC superfamily
• Not a pump, but rather a transport of Cl- coupled to both ATP hydrolysis & ATP binding
• Epithelial cells of lung
• Allows water to flow out in response to outward movement of ions, hydrating mucous layer
• Layer captures bacteria & is easily washed away from airways

Question 14

∆F508

Answer 14

• Accounts for ~70% of CFTR mutations in the US
• Protein doesn’t fold at body T, but folds & is functional at lower T

Question 15

∆G551D

Answer 15

• Accounts for 4% of CFTR mutations
• Channel reaches cell surface but doesn’t open properly
• Kalydeco is an approved drug keeping channel open

Question 16

Voltage-gated ion channels

Answer 16

• Respond to changes in electric potential across membrane
• Found in all nerve cells, also found in muscle cells, egg cells & plants
• Opening of channel further changes membrane potential, can either activate / inactivate other voltage - gated channels

Question 17

Ligand-gated ion channels

Answer 17

• Respond to binding of a ligand e.g. a neurotransmitter or inward-rectifying potassium channels (Kir) that respond to the intracellular ligand PiP2

Question 18

Mechanically-gated ion channels

Answer 18

• Respond to mechanical force
• Auditory hair cells use this: Sound waves cause channel to open, causing ion flow that affects voltage-gated channels who transmit signal to brain