Cell membrane transport

Question 1

Describe uniport, symport and antiport modes of transportation

Answer 1

Uniport: One molecule is transported into the cell
Symport: Two different molecules are transported into the cell.
Antiport: One molecule is taken into the cell while the another molecule is simultaneously taken out of the cell.

Question 2

List the factors affecting diffusion

Answer 2

Concentration gradient
Mass of molecules
Solvent density
Membrane permeability
Surface area and thickness of membrane
Temperature
Pressure

Question 3

What are the types of passive diffusion?

Answer 3

-Simple diffusion
Facilitated diffusion
Osmosis

Question 4

Define osmosis

Answer 4

Movement of water from a region of high water concentration (or low solvent concentration) to a region of low water concentration (or high solvent concentration) across a semi-permeable membrane.

Question 5

What is osmotic pressure?

Answer 5

Pressure required to stop osmosis

Question 6

What is osmolality?

Answer 6

The concentration of a solution expressed as the total number of solute particles per kilogram.

Question 7

What is tonicity?

Answer 7

The ability of an extracellular solution to make water move into or out of a cell by osmosis.

Question 8

What happens when a cell is placed in a hypertonic solution?

Answer 8

Water moves from the cell to the surrounding solution

Question 9

What happens when a cell is placed in a hypotonic solution?

Answer 9

Water moves from the surrounding solution to the cell by osmosis, causing the cell to burst

Question 10

What happens when a cell is placed in an isotonic solution?

Answer 10

No net movement of water

Question 11

What is active transport?

Answer 11

Use of energy to transport molecules into or out of the cell against concentration gradient

Question 12

Differentiate between primary and secondary active transport

Answer 12

Primary active transport uses ATP to transport molecules into the cell
Secondary active transport uses energy derived secondarily from energy that has been stored in the form of ionic concentration differences of secondary molecular or ionic substances between the two sides of a cell membrane, created originally by primary active transport.

Question 13

Give an example of primary active transport

Answer 13

Sodium-potassium pump
Pumps Na+ outward and K+ inward
Carrier protein: 2 globular proteins
3 binding sites for Na+
2 binding sites for K+
ATPase activity near Na+ binding site
Controls cell volume

Question 14

Name 2 other primary transporters

Answer 14

H+ : Gastric glands, late distal tubules of kidney

Ca2+ : sarcoplasmic reticulum of muscles

Question 15

Give an example of co-transport (secondary active)

Answer 15

Glucose-Na+ co-transport
“Symport pump”
Glucose “piggy backs” on Na+
No ATP used to transport ATP
ATP was used to transport NA+ to create gradient

Question 16

Give an example of counter-transport (secondary active)

Answer 16

Na+/Ca2+ —–> proximal tubules

Question 17

Describe exocytosis

Answer 17

• Vesicles containing molecules are transported from within the cell to the cell membrane
• The vesicle membrane attaches to the cell membrane.
• Fusion of the vesicle membrane with the cell membrane releases the vesicle contents outside the cell.

Question 18

Explain the three types of exocytosis

Answer 18

Constitutive: Regular secretion of molecules, performed by all cells. Functions to deliver membrane proteins and lipids to the cell’s surface and to expel substances to the cell’s exterior.

Regulated: Relies on the presence of extracellular signals for the expulsion of materials within vesicles. Regulated exocytosis occurs in secretory cells and not in all cell types. Secretory cells carry neurotransmitters, hormones and digestive enzymes.

Lysosomal: Fusion of vesicles within lysosomes. Lysosomes contain acid hydrolase enzymes —-> breaks down waste, microbes and cellular debris

Question 19

Explain the process of exocytosis

Answer 19

Trafficking: Vesicles transported to cell membrane along microtubules of the cytoskeleton (motor proteins)
Tethering: Vesicle linked to and pulled into contact with the cell membrane.
Docking: attachment of the vesicle membrane with cell membrane. Phospholipid bilayers of the vesicle membrane and cell membrane begin to merge.
Priming: Occurs in regulated exocytosis and not in constitutive exocytosis. Specific modifications (signalling) that must happen in certain cell membrane molecules for exocytosis to occur.
Fusion: Vesicle membrane fully fuses with the cell membrane (ATP requiring). The fusion of the membranes creates a fusion pore. In kiss-and-run fusion, the vesicle temporarily fuses with the cell membrane to create a fusion pore and release its contents to the exterior of the cell. The vesicle then pulls away from the cell membrane and reforms before returning to the interior of the cell.

Question 20

What are the functions of endocytosis

Answer 20

Procure the nutrients for cellular growth and repair,
Seize the toxin or unwanted pathogens and eventually neutralize them in the cells
Eliminate the old or non-functional cells