Ch.12: Transport Across Membranes

Question 1

Things unlikely to diffuse across the membrane?

Answer 1

Lipid bilayers are selectively permeable
- polar molecules: H2O, glycerol
- large molecules: amino acids, glucose
-ions: H+, Na+, K+, Ca2+

Question 2

Things likely to diffuse across the membrane?

Answer 2

• small non polar molecules
  ex. O2, CO2, N2, steroid, hormones
  -simple diffusion

Question 3

Cells build gradients
-concentration across membrane?
-what molecules?

Answer 3

• different conc. can be generated across a membrane
• only applies to molecules that can’t simply diffuse

Question 4

Membrane potential

Answer 4

the voltage differences across the membrane
- building of ions across a membrane can generate

Question 5

Resting Membrane Potential

Answer 5

=-20 to -200mV
- Inside of cell is more negative due to large amounts of negatively charged DNA and Proteins

Question 6

Two main classes of membrane transport proteins?

Answer 6

• channel proteins
• transporter/carrier proteins

Question 7

Channel Proteins
- selectivity
- shape
- molecules

Answer 7

• selectivity: size and charge
• shape: stay the same (pore)
• molecules:typically ions

Question 8

Transporter (Carrier) Proteins
- selectivity
- shape
- molecules

Answer 8

• selectivity: binding site specificity
• shape: changes shape to transport molecules
• molecules: most other small molecules
• typically selective for one type of solute

Question 9

Passive Transport
- Movement w/ respect to concentration:
- Energy Requirement:
- Proteins Types:

Answer 9

• Movement w/ respect to concentration: high to low only
• Energy Requirement: no
• Proteins Types: channel mediated or transporter mediated

Question 10

Active Transport
- Movement w/ respect to concentration:
- Energy Requirement:
- Proteins Types:

Answer 10

• Movement w/ respect to concentration: low to high
• Energy Requirement: yes
• Proteins Types: pump (special transporters)

Question 11

What effects movement of charged molecules?

Answer 11

• concentration gradient
• membrane potential/electrical charge

Question 12

Aquaporins

Answer 12

channel proteins that greatly increase the rate of passage of water molecules
- up to 3 billion water molecules pass through a single aquaporin per second

Question 13

Osmosis

Answer 13

water flows from low to high solute concentration
- dictates water flow in and out of cell
- cells have a higher concentration of solutes than their surroundings
- cells must protect themselves from swelling

Question 14

Hypertonic Solution

Answer 14

As the solute concentration in the solution is greater than inside the cell
- water will exit and the water loss causes the cell to shrink in size

Question 15

Isotonic Solution

Answer 15

No water is lost or gained as the concentrations of solutes are the same inside and outside of the cell

Question 16

Hypotonic Solution

Answer 16

as the solute concentration in the solution is less than that inside the cell
- water will enter the cell and cause it to swell
- big problem because cell will burst

Question 17

ATP-Driven Pump

Answer 17

uses energy released by ATP hydrolysis to curve uphill transport of solute

Question 18

Glucose Transporter/Carrier Proteins

Answer 18

glucose transporters passively transport glucose down its concentration gradient

Question 19

Gradient-Driven Pump

Answer 19

links uphill transport of one solute to the downhill transport of another

Question 20

Transport against concentration gradient

Answer 20

requires a pump

Question 20

Light-Driven

Answer 20

energy from sunlight drives transport (seen in bacteria)

Question 21

Na+/K+ pump

Answer 21

an ATP-driven pump that moves Na out of the cell and K into the cell
- helps maintain Na/K gradient
- large amounts of sodium out side of cell and potassium inside the cell

Question 22

What uses 30% of the ATP produced in the body?

Answer 22

Na/K pump

Question 23

What do Gradient Driven Pumps do and what are the types?

Answer 23

pair transport of molecules
types: symport vs. antiport

Question 24

symport vs antiport

Answer 24

symport: two molecules moving out/ moving in the same direction
antiport: two molecules moving in opposite directions

Question 25

Ion channels and membrane potential
- What determines what can go through channels

Answer 25

• selectivity filter: based on diameter, shape, charge distribution
• gated: can be opened and closed

Question 26

Different types of gated ion channels respond to different stimuli

Answer 26

• voltage gated
• ligand-gated (extracellular ligand)
• ligand-gated (intracellular ligand)
• mechanically gated

Question 27

What is the sodium potassium pumps function?

Answer 27

it functions to move Na out of the cell and K into the cell to help maintain the Na/K gradient

Question 28

What factors can ion channels gate for?

Answer 28

diameter, shape, and charge distribution

Question 29

How many ion of each are transferred in one “pump” of the Na/K pump?

Answer 29

3 sodium ions leave the cell and 2 potassium ions enter the cell

Question 30

Which type of proteins are used in active transport, carrier/transporter proteins or channel proteins? Why?

Answer 30

Because unlike channel proteins, carrier proteins close and open, binding to molecules and changing their shape to push the molecules across..

Question 31

Explain how FRAP works?

Answer 31

In FRAP, cell membrane proteins were modified to glow fluorescent green. Then, a laser was shined on part of the cell membrane proteins which destroyed their ability to glow green. However, overtime the green proteins moved to the dark area and the non-green proteins spread out and the whole membrane was mostly green again.