Hillard

Question 1

Overview

Answer 1

1. much of cell signaling initiated by binding of small molecules to receptors
2. difference in distance from site of release and target define the types of signaling
3. different time courses

Question 2

Ionotropic receptors TRP channels

Answer 2

NT’s and sensory stimuli utilize this cell signaling method

The receptor transducer and amplifier are combined and release messengers such as Ca2+, Na+, and Cl-

Question 3

Voltage-operated calcium channels

Answer 3

Electrical signals like membrane depolarization active use these

Change in membrane potential (depolarization) opens Ca2+ channels flowing the cell with Ca2+ which acts as a messenger

Question 4

GPCR

Answer 4

Acted on by NTs and hormones

1. GPCR is bound by ligand
2. conformational change in alpha and beta/gamma subunit inside cell GDP exchanged for GTP
3. signal amplified by AC
4. AC stimulates production of cAMP

Or amplifier is PLC and second messengers are DAG and InsP3 and Ca2+

Question 5

Genomic and nongenomic action of steroid hormones

Answer 5

Both of these happen in the cell

Genomic action: receptor, transducer, and messenger are all in one and the amplification is through regulation of gene transcription

Nongenomic action: GPCR

Question 6

Tyrosine kinases and serine/threonine kinases

Answer 6

TK: Growth and survival factors

Use transducers, amplifiers and messengers

S/T Kinases: transforming growth factor B superfamily

Combined transducer and amplifier

Question 7

Summary of chemical cell signaling

Answer 7

• greater variety of ligands and signaling motifs
• effective way to interfere selectively with a signaling pathway is to mimic or inhibit the ligand binding event
• trying to alter signaling motif can result in off target effects

Question 8

Small molecular weight amines as ligands

Answer 8

• ACh, glutamate, NE, and dopamine
• stored and released in vesicles
• mech for tight regulation of amount released; inactivation
• fast or medium transmission

Question 9

Lifecycle of ACh

Answer 9

• ACh synthesized by ChAT
• packaged into vesicles by VAChT
• once in synapse used to signal or degraded by AChE
• AChE degrade ACh into acetate and choline
• Choline imported back into the cell via the CHT (choline transporter)
• CHT rate-limiting step of this process
• Neuromuscular junction used ACh
• Release from vesicles is regulated by calcium

Question 10

Pathway of epinephrine synthesis

Answer 10

Tyrosine (TH with cofactor TTHP) > DOPA > Dopamine > NE > Epinephrine

First rxn is rate-limiting step

Question 11

Peptides as ligands

Answer 11

• Common in nervous system
• Large
• Not released using synaptic vesicles but through secretory pathway
• synthesized as large precursors

(example: chemokines)

Question 12

Lipid signaling molecules

Answer 12

• membrane soluble
• made on demand
• derivatives of arachidonic acid
• targets can be intracellular and membrane

EX: 2-arachidonoylglycerol (2-AG)

Question 13

Gaseous molecules

Answer 13

-can diffuse freely through membranes and water

EX: NO (important transmitter in vasculature)

Question 14

Steroid hormones

Answer 14

Cholesterol can be converted into cortisol or aldosterone

Question 15

PARs

Answer 15

• thrombin receptors
• important in blood clotting
• ligand is part of receptor
• peptide ligand gets cleaved off by thrombin causing activation of receptor

Question 16

Equation explaining ligand and receptor relationship

Answer 16

Ligand + Receptor = LR complex = effect

Question 17

What does binding involve?

Answer 17

• overcoming Brownian motion of the ligand in solution
• breaking H bonds between ligand and water
• energy required to transduce the receptor

Question 18

Ligand binding to receptor and the law of mass action

Answer 18

Law of mass action: proposition that the rate of a chemical reaction is directly proportional to the product of the activities or concentrations of the reactants

k1: rate constant for association
k2: rate constant for dissociation

Question 19

Equilibrium

Answer 19

k1 [L] * [R] = k2 [LR]

k2 / k1 = [L] * [R] / [LR]

k1 / k2 = Kd

Question 20

Kd

Answer 20

• Equilibrium dissociation constant
• goodness of fit
• inversely related to affinity of L for receptor
• units are concentration
• when [L] is large, [LR] = Rt
• when [L] = Kd, [LR] = 1/2 Rt

Question 21

Fractional occupancy of receptor by ligand at equilibrium

Answer 21

[LR] / Rt

-under most physiological conditions, the fractional occupancies of receptors by their ligands is very small

Question 22

Saturation binding assay

Answer 22

• performed at equilibrium
• used to determine Kd value for LR complex
• can be used to estimate total # of receptors (Rt)
• determine LR at various conc of L
• if need to determine time to equilibrium, use lowest [L]

Question 23

Competition among ligands

Answer 23

• Reversible competitive
• Irreversible competitive
• Noncompetitive
• Partial agonist/antagonist

Question 24

Random Tidbits

Answer 24

-Usually, all receptors do not need to be bound to produce maximal effect