Lecture 12 part 2

Question 1

Sensory transduction in vision

Answer 1

rods and cones are responsible for detection of light

Question 2

Rods

Answer 2

sense low levels of light but cannot discriminate colors

Question 3

Cones

Answer 3

less sensitive to light but can discriminate colors.

Question 4

Outer segment of rods and cones contain what?

Answer 4

loaded with rhodopsin

Question 5

Inner segment of rods and cones contain what?

Answer 5

produces ATP required to maintain the membrane potential needed for phototransduction. Potential is established by the Na-K ATPase

Question 6

cGMP and rod cells

Answer 6

Degradation of cGMP, caused by light, closes the ion gated channel (of Na and Ca) and hyperpolarizes the cell.

Question 7

In dark, cGMP levels and membrane potential

Answer 7

high concentration.

-45 mV. Since channels are open, cant get to -70.

Question 8

In light, cGMP levels and membrane potential

Answer 8

cGMP is degraded, channels close. hyperpolarizes to -75.

Question 9

Rhodopsin and what happens in light

Answer 9

integral membrane protein in the outer segment. In light, converts 11-cis-retinal to all-trans-retinal, causing a (cc) and thus interacts with transducin

Question 10

Transducin when not bound with rhodopsin (cis retinal)

Answer 10

heterotrimeric G-protein that binds GDP in the dark.

Question 11

Transducin when bound with rhodopsin (trans retinal)

Answer 11

binds GTP and dissociates into alpha and beta-gamma. Alpha associates with cGMP phosphodiesterase (PDE) which converts cGMP to 5’-GMP

Question 12

cGMP phopshodiesterase (PDE)

Answer 12

converts cGMP to 5’-GMP. cGMP cant bind to channels, closing the channels, causing the hyperpolarization of the cell.

Question 13

Olfaction uses what type of receptors?

Answer 13

G protein-coupled receptors

Question 14

Binding of an odorant causes what?

Answer 14

causes replacement of GDP by GTP on the G protein, which then activates AC, raising cAMP.

Question 15

Phosphorylation of G-protein olfactory molecule causes what?

Answer 15

will inactivate the receptor, causing it to be recycled and then being put back onto the membrane. This is a form of desensitization.

Question 16

cAMP causes what in the olfaction mechanism?

Answer 16

opens the cAMP-gated Na and Ca channels and depolarizes the cell as Na and Ca rush into the cell.

Question 17

Gustducin

Answer 17

G protein in taste. cAMP produced, activation of PKA, and phosphorylation of K channels, causing them to close.

Question 18

K channels closing in taste causes what?

Answer 18

reduced outflow of K causes depolarization and the signal is sent to the brain.

Question 19

2 types of gated ion channels

Answer 19

voltage gated and ligand gated

Question 20

2 general ways to depolarize a membrane

Answer 20

influx of positively charged ions or efflux of negatively charged ions

Question 21

High [Na] is where and flow in which direction

Answer 21

outside the cell.

flow into the cell.

Question 22

High [K] is where and flow in which direction

Answer 22

inside the cell. flow out of the cell.

Question 23

High [Ca] is where and flow in which direction

Answer 23

outside the cell. flow into the cell.

Question 24

High [Cl] is where and flow in which direction

Answer 24

outside the cell. but flow out of the cell since lots of negative charge already in the cell.

Question 25

Voltage gated Na channel structure

Answer 25

4 domains clustered around a central pore. 4 helices (voltage sensors - one from each domain) carries a positive charge, keep the channel closed when negative potential.

Question 26

Depolarization and the voltage gated Na channel

Answer 26

the voltage sensing helices move toward the outside of the membrane, opening up the channel, allowing Na to flood in. Tethered ball will plug the channel shortly after opening

Question 27

What type of residues would you see in the core of the Na channel?

Answer 27

Hydrophobic since they need to move sodium ions.

Question 28

Residues in the voltage sensing helix?

Answer 28

heavily positively charged (lysine, arg)

Question 29

Tethered ball and its affinity

Answer 29

high affinity to binding in the pore region when the pore is open.

Question 30

Resetting the tethered ball

Answer 30

membrane is repolarized, pull down the voltage sensing helices, closing the channel and squeezing out the ball.

Question 31

Voltage gated Na channel selectively

Answer 31

Potassium ions are too large and anions are repelled from going through.

Question 32

Hydrated potassium interacts with what in K channel pore?

Answer 32

carbonyl groups

Question 33

What opens the voltage-gated K channel?

Answer 33

arg-containing helices (voltage sensors) that open and close.

Question 34

Acetylcholine receptor channel structure

Answer 34

5 subunits to create a central pore. Pore is normally held closed by leucine side chains that extend into the middle and block ion passage.

Question 35

Binding of acetylcholine to the ligand gated ion channel

Answer 35

causes a (cc), twisting of subunits, that moves the hydrophobic side chains out of the pore and allows ion passage.

Question 36

What ions flow through a acetylcholine ligand gated ion channel?

Answer 36

sodium, potassium, and calcium

Question 37

How many acetylcholines need to cause a (cc)?

Answer 37

2

Question 38

Steroid hormone receptor

Answer 38

Hormone is carried by serum binding proteins across the plasma membrane and bind to specific receptors in the nucleus (Rec). Rec (cc) binds to other hormone-receptor complexes and binds to hormone response elements (HREs)

Question 39

Hormone receptor complexes (HREs)

Answer 39

specific regulatory regions in the DNA that are adjacent to specific genes. Can act as an inhibitor or activator

Question 40

Eicosanoids

Answer 40

lipid signaling molecule. paracrines (act locally). affect function, inflammation, fever, pain, blood clot formation, gastric acid secretion.

Question 41

3 types of eicosanoids

Answer 41

prostaglandins, thromboxanes, and leukotrienes

Question 42

Prostaglandins

Answer 42

bind to G protein receptors and affect cAMP levels. NSAIDS prevent synthesis

Question 43

Prostaglandins’ clinical activity (4)

Answer 43

stimulate uterine contraction, affect blood flow to specific organs, elevate body temp, and cause inflammation and pain.

Question 44

Thromboxanes

Answer 44

bind to thromboxane receptors, G-protein coupled receptors. NSAIDS inhibit

Question 45

Thromboxanes’ clinical activity (2)

Answer 45

produced by platelets and act in the formation of blood clots and restriction of blood flow

Question 46

Leukotrienes

Answer 46

primarily act on GPCR, other receptors too.

Question 47

Leukotrienes’ clinical activity (3)

Answer 47

induce constriction of lung airways, overproduction can cause asthmatic attack, and allergic rxn can cause a strong contraction of the smooth muscle of the lung (anaphylactic shock)