L16 - Transport across cell membranes

Question 1

What are the different types of transport across cell membranes

Answer 1

Non mediated transport, mediated transport, passive transport, active transport, vesicular transport

Question 2

What is non-mediated transport

Answer 2

Does not directly use a transport protein
Important for absorption of nutrients and excretion of wastes

Question 3

What molecules use non-mediated transport

Answer 3

Nonpolar, hydrophobic molecules (e.g oxygen, CO2, nitrogen, fatty acids, steroids, small alcohols, ammonia and fat-soluble vitamins)

Question 4

What is mediated transport

Answer 4

Moves materials with the help of a transport protein

Question 5

Describe the structure of ion channels

Answer 5

Water filled pore lined by hydrophilic amino acids
This shields the ions from the hydrophobic core of the lipid bilayer

Question 6

What is ionic selectivity

Answer 6

There are specific amino acids lining water filled pores, allowing it to be selective to a particular ion (via ion selectivity filter)
Specificity can be based on atomic radius

Question 7

What are stimuli that control opening of ion channels

Answer 7

Voltage, ligand binding, cell volume, pH, phosphorylation

Question 8

What is the patch clamp technique

Answer 8

A way to isolate and measure one single ion channel
By taking a piece of glass, and sticking it on the cell causing the membrane to be sucked into the pipette

Question 9

What is carrier mediated transport

Answer 9

When the transporter undergoes a conformational change due to protein binding to transport protein

Question 10

Is mediated transport passive or active

Answer 10

Can be both

Question 10

What are properties of carrier mediated transport proteins

Answer 10

Specificity, inhibition, competition, saturation

Question 11

What are the steps of faciliated diffusion of glucose

Answer 11

Glucose binds to transport protein (GluT)
Transprot protein changes shape and glucose moves across cell membrane
Kinase enzyme reduces concentration inside cell by converting glucose into glucose-6-phosphate

Question 12

What are the two forms of active transport

Answer 12

Primary active transport - energy is directly derived from ATP hydrolysis
Secondary active transport - energy stored in an ionic concentration gradient is used to drive active transport of other substances against concentration gradient

Question 13

What percentage of cell energy is used on primary active transport

Answer 13

~30%

Question 14

Describe the Na/K ATPase pump

Answer 14

3 Na+ ions removed from cell, 2K+ brought into cell - pump generates a net current and is electrogenic

Question 15

What are examples of secondary active transporters

Answer 15

Na+ antiporters (Ca2+ or H+)
Na+ sympoters or cotransporters (same direction into cell, glucose or amino acids)