Topic 3B - Transport Across Membranes

Question 1

what passes via diffusion?

Answer 1

hydrophobic small and uncharged molecules

Question 2

what do transporters and channels let through?

Answer 2

inorganic ions, small organic polar molecules

Question 3

three types of active transport

Answer 3

coupled transport
ATP-driven pumps
light-driven pumps

Question 4

symport vs antiport

Answer 4

piggyback vs go in opposite directions

Question 5

what is an example of a symporter that we discussed in class?

Answer 5

Na+-glucose symport for maintaining low [Na+] in cell

Question 6

what are the three classes of ATP-driven pumps?

Answer 6

P-type, V- and F-type, and ABC transporter

Question 7

what kind of pumps are the Ca2+ pump and the Na-K pump examples of? And what do these pumps do?

Answer 7

P-type pumps: phosphorylate and transport ions. Pump Ca and Na out of cell

Question 8

ABC transporters in eukaryotes vs prokaryotes?

Answer 8

eukaryotes = mainly export
prokaryotes = important for export/ import

Question 9

what type of directional transport are ABC transporters

Answer 9

unidirectional!

Question 10

what type of things do ABC transporters transport?

Answer 10

ions, peptides, sugars, amino acids (small molecules)

Question 11

difference between V and F type ATP-driven pumps?

Answer 11

V type = produce ADP from ATP

F type = produces ATP

Question 12

Characteristics of Ion Channels

Answer 12

high selectivity/ narrow
gated
high efficiency!!!
ALWAYS PASSIVE

Question 13

what are the different types of gated ion channels

Answer 13

voltage, extracellular ligand, intracellular ligand, mechanically (mechanosensitive)

Question 14

how is the membrane potential in animal cells created?

Answer 14

K+ leak channel

Question 15

how does K+ leak channel specificity work?

Answer 15

free carbonyl oxygens at selectivity filter allow dehydrated potassium to pass but sodium cannot pass because they will not be able to interact with the carbonyl oxygens as dehydrated molecules and they are too large to pass with their hydrate shells

Question 16

how does the Na+ channel handle selectivity?

Answer 16

conducts mostly hydrated forms so Na fits and K is too big to pass

Question 17

how do aquaporins work? structure and function

Answer 17

have hydrophilic and hydrophobic side –> hydrophilic side allows for water molecules to line up in single row and hydrophobic side makes pore too narrow for hydrated ions to enter
rapid transport of water molecules and blockage of ions (ions create osmotic gradient)
found in areas that excrete lots of water

Question 18

in what type of channels is arginine important?

Answer 18

aquaporins (make more impermeable to hydrogen ions)

Question 19

which channel has lateral ports?

Answer 19

voltage-gated Na+ channel

Question 20

which type of channels open in an all or nothing fashion and have three distinct phases?

Answer 20

voltage-gated cation channels.

Question 21

why is the inactive state of voltage-gated cation channels so important?

Answer 21

prevents signal from propagating backwards…

Question 22

what did the patch clamp technique verify

Answer 22

that voltage-gated cation channels open in all or nothing fashion

Question 23

what are transmitter-gated ion channels used for

Answer 23

converting extracellular chemical signals into electrical signals

Question 24

what are the two types of neurotransmitters and to which ion channels are they related to?

Answer 24

excitatory and inhibitory neurotransmitters. related to transmitter-gated ion channels

Question 25

what do excitatory neurotransmitters do?

Answer 25

open cation channels so the membrane depolarizes (more positive inside)

Question 26

what do inhibitory neurotransmitters do?

Answer 26

open channels that make it more difficult for cell to depolarize (inside more negative)

Question 27

what types of pumps and receptors are involved in muscular contractions

Answer 27

Na and Ca and acetylcholine receptors

Question 28

does acetylcholine have high or low selectivity among cations?

Answer 28

low

Question 29

how can acetylcholine receptors affect operations

Answer 29

block them to relax muscles