Biochemistry - Transport Mechanisms

Question 1

Energy of passive vs active transport

Answer 1

• Passive: no energy required
• Active: energy required

Question 2

Movement of materials relative to concentration gradient (passive vs active)

Answer 2

• Passive: high to low (with concentration gradient)
• Active: low to high (against concentration gradient)

Question 3

Simple diffusion

Answer 3

• Net movement of materials from an area of high to low concentration
• All gas and liquid particles partake in it all the time
• Random

Question 4

Facilitated diffusion

Answer 4

• Transport of ions and polar molecules through a membrane via protein complexes
• Channel proteins or carrier proteins may be used

Question 5

Osmosis

Answer 5

• Passive diffusion of water across a membrane
• Water moves from an area of low solute concentration to an area of high solute concentration
• Results in equal solute concentrations on either side of membrane

Question 6

Factors that affect the rate of diffusion

Answer 6

• Temp: more heat = faster movement of particles
• Distance travelled: smaller distance = faster movement
• Mass of particles: lower mass = less energy needed to make them move faster
• Density of medium: denser medium = more difficult for particles to move through it, diffusion through gas is faster than liquid
• Concentration gradient: the bigger the difference, the steeper the concentration gradient, the faster the molecules will diffuse

Question 7

Equilibrium (net movement of materials)

Answer 7

Molecules of a substance are moving equally in both directions (equal concentrations in both areas)

Question 8

Channel proteins

Answer 8

Provide a “tunnel” through the membrane through which the molecules can diffuse

Question 9

Carrier proteins

Answer 9

Change shape when their specific particle binds, change of shape moves particle across membrane

Question 10

Isotonic solution

Answer 10

• Concentration of solutes is equal on both sides
• Water moves back and forth but amount of water on each side doesn’t change

Question 11

Hypotonic solution

Answer 11

• Less solutes outside the cell than inside
• Water moves into the cell

Question 12

Hypertonic solution

Answer 12

• More solutes outside the cell than inside
• Water moves out of cell

Question 13

Aquaporin

Answer 13

• Membrane proteins that provide a means for water to travel through a membrane following its concentration gradient
• Specific to water because water is polar and cannot directly diffuse through cell membrane

Question 14

Primary active transport

Answer 14

• Energy in form of ATP molecules is used to move materials across membrane
• ATP is used to change shape of transport protein, allowing it to shuttle materials across membrane
• Creates concentration gradient (represents stored energy that can be used for secondary active transport)

Question 15

Secondary active transport

Answer 15

• Uses energy of high concentration gradient of one substance to move other substances across membrane
• May use concentration gradient to shuttle substances in same direction (symport proteins) or in opposite directions (antiport proteins)

Question 16

Influence of ATP on membrane proteins

Answer 16

• Energy from ATP molecule is used to change conformation of transport proteins, allowing them to shuttle substances across cell membranes

Question 17

Example of primary active transport

Answer 17

Na/K Pump
- Necessary for nerves + muscles to function
- Pump binds to 3 sodium ions and ATP molecule
- ATP splitting provides energy to change channel shape, sodium ions are driven through channel
- Sodium ions released outside of cell membrane, new shape of channel allows 2 potassium ions (from outside) to bind
- Release of phosphate allows channel to revert to its original form, releasing potassium ions on inside of membrane

Question 18

Proton pump

Answer 18

• ATP is used to move H+ ions across membrane, building up a concentration gradient
• Creates a charge gradient and pH gradient

Question 19

Symport protein

Answer 19

• Secondary active transport
• Shuttles substances in the same direction

Question 20

Antiport protein

Answer 20

• Secondary active transport
• Shuttles substances in the opposite directions

Question 21

Exocytosis

Answer 21

• Secretory vesicles move through cytosol + contact cell membrane
• Vesicle membrane fuses with cell membrane, releasing contents of vesicle into cell exterior
• All eukaryotic cells partake in exocytosis

Question 22

Endocytosis

Answer 22

• Proteins + other substances trapped in pit-like depression that bulges inward from cell membrane
• Depression pinches off as an endocytic vesicle
• Three pathways: bulk-phase, receptor-mediated, phagocytosis
• Most eukaryotic cells partake in endocytosis

Question 23

Bulk-phase endocytosis

Answer 23

• Extracellular water taken in along with molecules in solution in the water, membrane folds inward which encloses solute and water molecules

Question 24

Receptor-mediated endocytosis

Answer 24

• Molecules (proteins or molecules carried by proteins) bind to outer cell surfaces by receptor proteins
• Receptors collect into a pit coated in clathrin (protein network) that reinforce cytosol side
• Pit breaks free, vesicle loses clathrin coating and may fuse with lysosome
• Enzymes within lysosome digest cargo, breaking down into smaller + useful molecules

Question 25

Phagocytosis

Answer 25

• Psuedopods engulf particles to be brought into cell, forming vesicle containing particles within cell
• Cells use phagocytosis to engulf bacteria, parts of dead cells, viruses, or other foreign particles