Membrane Transport

Question 1

How is chemical disequilibrium maintained across the plasma membrane?

Answer 1

The result of the permeability porperties of the plasma membrane and the actions of specific transport proteins

Question 2

How does cholesterol affect membrane permeability to water?

Answer 2

Low cholesterol = Higher water permeability

Question 3

What four things affect the rate of diffusion of a molecule through a lipid bilayer?

Answer 3

Membrane permeability

Surface area

Thickness

Concentration gradient

Question 4

What is an electrochemical gradient?

Answer 4

The combined effects of the concentration and electrical gradients across a membrane

Question 5

What are the three functional categories of membrane transport proteins?

Answer 5

Channels

Transporters

ATP-powered pumps

Question 6

What is the structure and function of a channel?

Answer 6

Transmembrane protein that forms a water-filled pore

Selective

Rapid

Gated

Flow occurs down the concentration gradient

Question 7

What is the structure and function of transporters (Carrier Proteins)

Answer 7

Bind substrate with high specificity

Do not form direct connection

Conformational change responsible for transport

Facilitated diffuciton

Question 8

What are uniporters?

Answer 8

Carriers that bind and transport only one type of substrate.

Form of facilitated diffusion

Question 9

What are cotransporters and how do they function?

Answer 9

Protein carriers that move more than one substrate at a time.

Often couple transport down a gradient with transport against a gradient

Secondary active transport

Question 10

What are the two types of cotransporters and what is the difference between them?

Answer 10

Symporters - move substrates in the same direction

Antiporters - move substrates in opposite directions

Question 11

Describe the function of ATP-powered pumps.

Answer 11

Use energy from ATP to move substrates against their concentration gradient.

Primary active transport

Question 12

What are aquaporins and what is their function

Answer 12

Family of integral membrane channels that selectively transport water

Question 13

What are the two types of ion channels?

Answer 13

Leak channels - always open

Gated channels - open and close in response to a stimulus

Question 14

What are the three ways ion channels are gated?

Answer 14

Voltage

Ligand

Mechanically

Question 15

How does the selectivity filter on voltage gated K channels work?

Answer 15

The hydration shell of K is displaced as K interacts with carbonyl oxygen groups lining the pore, allowing K to pass.

Na is too small and tends to remain hydrated

Question 16

How does the selectivity filter of a Na channel work?

Answer 16

Essentially a size filter unique to the ionic radius of Na

Question 17

What are three properties of carrier-mediated transporters?

Answer 17

Specificity

Competition (e.g. glucose and galactose

Saturation

Question 18

What is Kt in the rate equation for the transport of glucose through GLUT1?

Answer 18

Used to describe the affinity fo the glucose transporter for glucose

Question 19

What is GLUT4 regulated by and how does this affect transporter kinetics

Answer 19

GLUT4 is regulated by insulin —> induces translocation of GLUT4 to the plasma membrane

Increases Vmax

Question 20

What is SGLT1 an example of?

Answer 20

A symporter.

Transports glucose and sodium from the intestinal lumen into the cell

Glucose moves against its concentration gradient

Question 21

How is the Na gradient maintained for use by SGLT1?

Answer 21

Na/K ATPase at the basal surface of the plasma membrane

Question 22

The Chloride-Bicarbonate exchanger is an example of what kind of transporter?

Answer 22

Antiporter

Question 23

What are P-class pumps and what is an example?

Answer 23

P-class pumps are ion pumps made up of two a subunits, one of which gets phosphorylated during the transport cycle.

Question 24

What is the function digoxin and ouabain

Answer 24

Inhibit Na/K ATPase

Question 25

What is the function and role of V-class pumps?

Answer 25

Pump protons against their electrochemical gradient from the cytosol into intracellular organelles via ATP hydrolysis.

Lower the pH within the lumen of organelles.

E.g. osteoclasts use V-pumps to promote bone resorption

Question 26

What is the function and role of F-class proton pumps?

Answer 26

They utilize potential energy from the movement of protons down their electrochemical gradient to generate the formation of ATP.

Also know as ATP synthase

Question 27

What is the general structure of ABC transporters?

Answer 27

Two transmembrane domains that form pathways through which solutes cross and determine specificity

Two nucleotide binding domains or (ATP-binding cassette domains) that face the cytosolic side

Question 28

What function do ABC transporters usually serve in eukaryotes?

Answer 28

Exporters

Question 29

What does the exporter function of ABC transporter do for the cell?

Answer 29

Protect cells from the toxic effects various endogenous metabolites and xenobiotics

Question 30

What is the effect of multidrug resistant transporters?

Answer 30

The bestow multidrug resistance to tumor cells because they transport the drug out of cell, thus increasing the necessary dose of the drug to kill the cells.

Question 31

What are three factors that channel selectivity can depend on?

Answer 31

Charge of the ion

Size of the ion

Amount of water attracted to and retained by the ion (hydration shell)