Transport Across Cell Membranes

Question 1

what is secondary active transport?

Answer 1

movement of substances against their concentration gradient using the energy stored in an ion gradient, usually Na+, established by primary active transport

Question 2

what pump establishes the Na+ gradient for secondary active transport?

Answer 2

the Na+/K+ ATPase (sodium-potassium pump)

Question 3

what does the sodium-potassium pump do?

Answer 3

pumps 3 Na+ out and 2 K+ in, using ATP, creating an electrogenic gradient

Question 4

what are Na+-dependent symporters?

Answer 4

transporters that move Na+ and other substance into the cell together

Question 5

what are Na+-dependent antiporters?

Answer 5

transporters that move Na+ into the cell while exporting another ion, like H+ or Ca2+

Question 6

why is the sodium-potassium pump considered electrogenic?

Answer 6

because it creates a net outward positive charge by pumping more positive ion out than in

Question 7

what is facilitated diffusion?

Answer 7

passive movement of molecules across membranes via specific transport proteins without energy input

Question 8

what is the role of GLUT proteins?

Answer 8

facilitate the diffusion of glucose into the cell

Question 9

what are ion channels?

Answer 9

water-filled pores that allow passive diffusion of ions down their electrochemical gradient

Question 10

what is the pump-leak hypothesis?

Answer 10

the Na+/K+ pump continuously works to counteract ion leakage across the membrane

Question 11

what type of transport is mediated by carrier proteins but doesn’t use energy

Answer 11

facilitated diffusion

Question 12

why do ion channels transport ions so rapidly?

Answer 12

because ions do not bind to the channel

Question 13

what are the two main classes of membrane transport proteins?

Answer 13

channels and carriers

Question 14

what is Tmax?

Answer 14

the maximum rate of transport when all carrier binding sites are saturated

Question 15

name one method used to study/record ion channels

Answer 15

patch clamp technique

Question 16

why is secondary active transport considered “active” if it doesn’t directly use ATP?

Answer 16

because it moves substances against their gradients, powered by ion gradients that are maintained using ATP

Question 17

how does intracellular glucose concentration remain low despite facilitated diffusion?

Answer 17

glucose is phosphorylated to glucose-6-phosphate, preventing it from diffusing out and maintaining a gradient

Question 18

what would happen if the Na+/K+ pump stopped working?

Answer 18

Na+ gradients would dissipate, disrupting secondary transport, membrane potential, and cell volume regulation

Question 19

compare carrier and channel proteins in terms of speed and mechansism

Answer 19

channels are faster and allow bulk ion flow; carriers are slower and require conformational changes

Question 20

how does the Na+/H+ exchanger regulate pH?

Answer 20

by removing H+ from the cell in exchange for Na+ entry, reducing intracellular acidity

Question 21

why is active transport essential in epithelial cells?

Answer 21

it allows absorption of nutrients and ions even against concentration gradients, especially in the gut and kidneys

Question 22

what features make carrier-mediated transport similar to enzyme activity?

Answer 22

specificity, saturation kinetics, competition, and inhibition

Question 23

why can secondary active transport be symport or antiport?

Answer 23

because it can move molecules in the same or opposite directions relative to the driving ion

Question 24

how does membrane potential affect ion movement?

Answer 24

it adds an electrical component to the gradient, influencing ion direction and rate

Question 25

how is intracellular ion balance related to osmotic balance?

Answer 25

ion gradients regulate water movement, impacting cell volume and preventing lysis or shrinkage

Question 26

secondary active transport uses the potential energy stored in ___ gradients

Answer 26

Na+

Question 27

the Na+/K+ ATPase pumps ___ Na+ out and ___ K+ in

Answer 27

3; 2

Question 28

Na+-dependent symporters transport Na+ along with ___ or ___

Answer 28

glucose; amino acids

Question 29

carrier-mediated transport involves a ___ change in the protein to move the solute

Answer 29

conformational

Question 30

the sodium-potassium pump directly uses ___ to drive ion movement

Answer 30

ATP

Question 31

___ is a passive process that uses a transport protein without energy input

Answer 31

facilitated diffusion

Question 32

the glucose transporter family (GLUT) moves glucose ___ its concentration gradient

Answer 32

down

Question 33

ion channels are ___ pores that allow ion movement without binding the ion

Answer 33

water-filled

Question 34

carrier proteins exhibit saturation because they have limited ___ sites

Answer 34

binding

Question 35

the pump-leak hypothesis explain how the constant action of the pump balances ___

Answer 35

ion leakage

Question 36

voltage-gated ion channels open in response to changes in ___

Answer 36

membrane potential

Question 37

the ___ technique measures the activity of individual ion channels

Answer 37

patch clamp

Question 38

primary active transport uses ___ hydrolysis for energy

Answer 38

ATP

Question 39

in secondary transport, Na+ moves ___ its gradient, while glucose moves ___ its gradient

Answer 39

down; against

Question 40

intracellular phosphorylation of glucose reduces free glucose levels, maintaining the ___ gradient

Answer 40

diffusion