Cell Processes: Transport Across Cell Membranes

Question 1

What is non-mediated transport?

Answer 1

transport that doesn’t directly use a integral membrane transport protein (molecules are permeable across the hydrophobic core of phospholipid bilayer)

Question 2

What is mediated transport?

Answer 2

transport that moves materials with the help of a transport protein

Question 3

What is passive transport?

Answer 3

transport that moves substances down their concentration or electrochemical gradient with only their kinetic energy

Question 4

What is active transport?

Answer 4

transport that uses energy to drive substances against their concentration or electrochemical gradients

Question 5

What is vesicular transport?

Answer 5

transport that moves materials across membranes in small vesicles either by exocytosis or endocytosis

Question 6

What is non-mediated transport important for?

Answer 6

absorption of nutrients – excretion of wastes

Question 7

What type of molecules undergo non-mediated transport?

Answer 7

Nonpolar and hydrophobic molecules

Question 8

Examples of molecules that undergo non-mediated transport

Answer 8

oxygen, carbon dioxide, nitrogen, fatty acids, steroids, small alcohols, ammonia and fat-soluble vitamins (A, E, D and K)

Question 9

What is the function of ion channels?

Answer 9

mediate the movement of ions down their electrochemical gradient

Question 10

What is formed in the centre of an ion channel and what is its functions

Answer 10

a water filled pore that shields the ions from the hydrophobic core of the lipid bilayer

Question 11

Why is transport through the ion channel rapid?

Answer 11

ions do not bind to the channel pore (passive diffusion)

Question 12

What determines what ions can pass through an ion channel (ionic selectivity)

Answer 12

certain amino acids lining the pore determine

Question 13

What is ionic selectivity?

Answer 13

ion channels only allow certain ions to pass through

Question 14

What is the result of channels being ion selective?

Answer 14

the channel can harness the energy stored in the different ion gradients

Question 15

Why can ion channels NOT be open all the time?

Answer 15

it would get rid of the ion gradient

Question 16

What do ion channels contain to control passage of ions

Answer 16

gates

Question 17

Examples of stimuli that control channel gate opening and closing

Answer 17

voltage, ligand binding, cell volume (stretch), pH, phosphorylation

Question 18

What is a patch clamp?

Answer 18

A sensitive voltage clamp method that permits the measurement of ionic currents flowing through individual ion channels

Question 19

Number of ions that are able to diffuse through one ion channel per second

Answer 19

1 million

Question 20

the current through a single ion channel

Answer 20

10^-12 amps

Question 21

How does carrier mediated transport work?

Answer 21

The substrate to be transported directly interacts with the transporter protein

Question 22

Is carrier mediated transport faster or slower than ion channels and why?

Answer 22

Slower because the transporter undergoes a conformational change

Question 23

What is the general function of carrier mediated transport?

Answer 23

to take one molecule from one side of the membrane to the other

Question 24

Carrier proteins exhibit these 4 properties

Answer 24

specificity, inhibition, competition, saturation

Question 25

Is carrier mediated transport active or passive?

Answer 25

it can be both

Question 26

What does saturation mean for carrier mediated transporters?

Answer 26

They have only a certain number of binding pockets so they cannot intake anymore molecules that their binding pockets allow

Question 27

Does increasing concentration increase uptake with carrier mediated transporters

Answer 27

To a point, eventually it will reach a point where uptake is saturated

Question 28

Name of protein that takes up glucose

Answer 28

Glucose transporter protein (GLuT)

Question 29

Amount of glucose in blood

Answer 29

5

Question 30

Process of glucose moving into a cell

Answer 30

Glucose BINDS to transport channel protein > changes conformational shape of protein > allowing it to go into cell

Question 31

Does glucose move down its concentration gradient in facilitated diffusion?

Answer 31

Yes

Question 32

What is glucose converted into in the cell by a kinase enzyme?

Answer 32

glucose-6-phosphate

Question 33

Why is glucose converted into glucose-6-phosphate

Answer 33

to maintain glucose concentration gradient

Question 34

What cells do Facilitated diffusion of glucose

Answer 34

Muscle, nervous, fat cells

Question 35

what is GluT NOT called

Answer 35

do not call this a glucose channel that is doing passive diffusion (it is a carrier protein, passive facilitated diffusion)

Question 36

What is active transport?

Answer 36

An energy requiring process that moves molecules and ions against their concentration or electrochemical gradients

Question 37

What is primary active transport?

Answer 37

A form of active transport in which energy is directly derived from the hydrolysis of ATP to make ion gradients

Question 38

How much cell energy is used on primary active transport?

Answer 38

30%

Question 39

What is secondary active transport?

Answer 39

A form of active transport in which energy is stored in an ionic concentration gradient is used to drive the active transport of a molecule against its gradient

Question 40

Process of Sodium and Potassium ATPase

Answer 40

1. Na+ binds 2. ATP is split and Na+ is pushed out of the cell 3. K+ binds and phosphate is released 4. K+ is pushed in

Question 41

With a Na/KATPase, how many Na+ are removed

Answer 41

3 Na+ ions are removed from the cell

Question 42

With a Na/KATPase, how many K+ are brought into a cell

Answer 42

2 K+ ions are brought into the cell

Question 43

What is the result of a Na/KATPase

Answer 43

pump generates a net current and is electrogenic

Question 44

What does electrogenic mean

Answer 44

producing a change in the electrical potential of a cell.

Question 45

Other examples of ATPase ion pumps

Answer 45

Ca/K ATPase (Muscle SR), H/K ATPase (stomach)

Question 46

What does a Na pump do

Answer 46

maintains a low concentration of Na+ and a high concentration of K+ in the cytosol

Question 47

What type of transport is a Na pump

Answer 47

primary active transport

Question 48

What is a Na ion concentration gradient important for (6)

Answer 48

Maintain resting membrane potential Electrical excitability Contraction of muscle Maintenance of steady state cell volume Uptake of nutrients via secondary active transporters Maintenance of intracellular pH by secondary active transporters

Question 49

What is the pump-leak hypothesis

Answer 49

Na and K are continually leaking back into the cell down their respective gradients so the pump works continuously to maintain the ion gradient

Question 50

What type of transport are Na+ antiporter/exchangers

Answer 50

secondary active transport

Question 51

What do Na+ antiporter/exchangers do?

Answer 51

Allow Na+ ions to rush inwards and Ca2+ or H+ are pushed out

Question 52

What do Na+ symporter/cotransporters do?

Answer 52

Glucose or amino acids rush inward together with Na+ ions

Question 53

What are secondary active transporter powdered by?

Answer 53

Na+ gradient initially established by the Na pump