Lec. 6: Membrane Function: Passive and Active Transport

Question 1

Tonicity

Answer 1

Hypotonic- water into the cell (cell lyses)
Isotonic- net water in/out of the cell is equal (normal cell)
Hypertonic- water out of the cell (cell shrivels)

DUE TO WATER CONCENTRATION

Question 2

Osmosis

Answer 2

The diffusion of water across a permeable membrane

Question 3

Endocytosis

What are the 3 types?

Answer 3

Vesicle formed from the plasma membrane, bringing external molecules inside the cell

require ATP

Phagocytosis aka cell eating (creation of food vacuole), Pinocytosis aka cell drinking (coated vesicle which is smaller), receptor mediated (coated vesicles with solutes bound to receptors)

Question 4

Exocytosis

What is an example?

Answer 4

• Inernal membrane vesicle fuses with plasma membrane, releasing molecules to the extracellular space
• adds new components to the plasma membrane

require ATP

Neurotransmission

Question 5

Phagocytosis

Answer 5

Cell membrane engulfs large macromolecular structures

(to eat)

ie an amoeba engulfing a green algal cell

Question 6

Pinocytosis

Answer 6

Uptake of extracellular fluids and small molecules via endocytosis

(to drink)

Question 7

In a plant, what tonicity is preferred? What happens in the other tonicity’s?

Answer 7

Hypotonic solution is perferred as cell walls prevents lysing (bursting)
Isotonic results in a flaccid plant cell
Hypertonic plasmolyze (detachment from cell wall)

Question 8

What are the different types of traffic across the cell membrane called?

Answer 8

1. Direct passage through lipid bilayer (small, nonpolar, hydrophobic, UNCHARGED molecules,) NO ENERGY required
2. Transport proteins (Active or passive)
3. Vesicular Transport or Bulk Transport

Exocytosis- vesicle fuses with plasma membrane out the cell
Endocytosis- plasma membrane pinches inward forming a vesicle

Question 9

What does active transport require?

What is an example and how does it work?

Answer 9

Energy (ATP) AND a transport protein

CARRIER PROTEINS NOT CHANNEL

H+ is moved against concentration gradient and creates a voltage across the membrane

Question 10

Sodium/potassium pump

Answer 10

An electrogenic pump (generates a voltage) that maintains high inctracellular K+ and low Na+

3 Na+ out for 2 K+ in the bilayer (helps stabilize membrane potential)

Question 11

ATP structure

Answer 11

Adenine, ribose, 3 phosphate groups

Question 12

Co-transporters

Answer 12

gradient generated by one molecules which drives active transport of another

Ex. H+/sucrose cotransporter

Gradient of H+ ions as protons diffuse back as sucrose travels with it

Question 13

What is the transport of large molecules called?

Answer 13

Vesicular transport- for large molecules like proteins/carbohydrates

Question 14

What is the cause of hypercholesterolemia (high blood pressure)

Answer 14

• Deffective LDL receptors (lack of receptor mediated endocytosis)
• Accumulation and deposition of cholesterol and LDL in blood vessels
• Contributes to early atherosclerosis (hardening/thickening of arteries)