Lecture 7 - Crossing Membranes

Question 1

How do solutes cross membranes?

Answer 1

simple diffusion, facilitated diffusion, active transport

Question 2

What types of molecules diffuse freely?

Answer 2

small, uncharged molecules

Question 3

What types of molecules can’t diffuse freely?

Answer 3

large polar molecules, charged ions

Question 4

Simple diffusion

Answer 4

unassisted movement down the gradient

Question 5

Facilitated diffusion

Answer 5

protein mediated movement down the gradient
- does not require energy (ATP)
- it only moves molecules from high to low concentrations
- ex: glucose

Question 5

What types of proteins mediate facilitated diffusion?

Answer 5

• channels: pores, do not change structure as molecule passes through
• carriers: undergo a conformational change as solute moves

Question 6

Are carrier proteins highly specific to their solute?

Answer 6

yes

Question 7

How can carrier proteins transport two molecules?

Answer 7

coupled transport is used to transport one molecule against its concentration gradient by transporting it with a molecule along its gradient
- symport: molecules transported in same direction
- antiport: molecules transported in opposite direction

NO ATP

Question 8

What are the 3 types of hydrophilic transmembrane channels?

Answer 8

1. ion channels: specific to certain ions
2. porins: not very specific, only in mitochondria/chloroplast and bacteria
3. aquaporins: specific to H2O

Question 9

Ion channels

Answer 9

transmembrane proteins that allow rapid passage of specific ions
- typically gated

Question 10

What opens ion channels?

Answer 10

• voltage
• ligand
• temperature
• pressure

Question 11

How do potassium channels keep smaller ions out?

Answer 11

they have a filter
- potassium ion must shed its water molecule
- 8 oxygen atoms in the channel act as a replacement for the water molecules
- the ions move along the oxygen sites
- sodium ions are slightly smaller so they fail to interact with the oxygen atoms

Question 12

Why is passing ions important?

Answer 12

• membrane potential: the difference in the concentrations of ions on opposite sides of a membrane
  - cell membranes: -70 mV to -40 mV
• depolarization: interior voltage becomes less negative
• hyper polarization: interior voltage becomes more negative

cells read the change in voltage and use it as an intracellular signal

Question 13

Ligand-gated ion channels convert a ________ signal into the cell

Answer 13

chemical

Question 14

What are the four types of gated channels?

Answer 14

• ligand-gated
• temperature-gated
• pressure-gated
• voltage-gated

Question 15

Voltage-gated sodium channels

Answer 15

transmit signals in a wave through the nervous system