Transport Across Membrane

Question 1

What are some impediments to movement of a polar chemical from outside to inside a cell?

Answer 1

• Could be going against electrochemical gradient

- Need to get thru hydrophobic core of plasma membrane

Question 2

Compare passive diffusion and facilitated diffusion.

Answer 2

Passive diffusion does not require binding for transport, thus the concentration is proportionate to the rate of transport. Carrier-mediatied diffusion is a rectangular hyperbola that reflects the ability to saturate the receptors.

Question 3

Compare passive and active transport.

Answer 3

Passive does not require energy, whereas active transport does.

Question 4

What are some defining characteristics of GLUT 1, GLUT 4, and GLUT 5?

Answer 4

• GLUT 1 is the most ubiquitous at the glucose level of blood.
• GLUT 4 is insulin sensitive
• GLUT 5 carries fructose

Question 5

In active transport, what is the significance of a positive delta G? A negative delta G?

Answer 5

• Positive: requires energy

- Negative: Spontaneous

Question 6

What are 3 types of energy-linked transport processes?

Answer 6

• Driven by ATP hydrolysis
• Driven by ion gradients
• Drug Resistance genes - cancer (efflux pumps) i.e. p-glycoprotein

Question 7

What is the sodium potassium pump?

Answer 7

Pumps 3 sodiums out, and 2 potassiums in via a conformational shape change.

Question 8

What are ABC transporters?

Answer 8

ATP-Binding Cassette Transporters. Somewhere in their sequence is a structure that binds ATP. 49 total known in human genome.

Question 9

What is the difference between primary and secondary active transport?

Answer 9

If the active process uses chemical energy, such as from ATP, it is termed primary active transport. Secondary active transport involves the use of an electrochemical gradient.

Question 10

What is the mechanism of ionophores?

Answer 10

Transport ions across cell membrane and dissipate gradient.

Question 11

What are ligand-activated ion channels?

Answer 11

A group of transmembrane ion channel proteins which open to allow ions such as Na+, K+, Ca2+, or Cl- to pass through the membrane in response to the binding of a chemical messenger (i.e. a ligand), such as a neurotransmitter.

Question 12

What are aquaporins?

Answer 12

Transmembrane proteins that allow water to be transported across the cell membrane.

Question 13

What is the difference between channels and pumps?

Answer 13

Channels are passive (using gradient), whereas pumps are active (going against gradient).

Question 14

Why are ion channels considered allosteric proteins?

Answer 14

Because they have an extracellular domain where ligands bind allosterically.

Question 15

What is responsible for the rising action potentials in neurons?

Answer 15

Sodium channels

Question 16

What channelopathy is associated with cystic fibrosis?

Answer 16

Phenylalanine deletion in the CFTR gene, causing a defect in the chlorine transporter.

Question 17

What ABC transporter is involved in drug resistance?

Answer 17

MDR PGY1 p-glycoprotein.

Question 18

A mutation in ABCA transporter causes what?

Answer 18

Tangiers Disease: abnormal HDL and LDL cholesterol metabolism.

Question 19

What are similarities between Na+, K+, and Ca++ channels?

Answer 19

24 transmembrane segments, 4 domains, and 1 segment in each domain having positive charge so it would change conformation in response to membrane potential.