Exam 1: Sharp and smoothly graded responses/G-protein coupled receptors

Sharper responses occur when....

a target molecule requires simultaneous binding of many effector molecules

Some cell responses increase gradually as the concentration of extracellular signal molecule increases, eventually reaching a plateau as the signaling pathway is saturated, resulting in a _________ response curve.

hyperbolic

In other cases, the signaling system reduces the response at low signal concentrations and then produces a steeper response at some intermediate signal concentration---resulting in a ___________ response curve.

sigmoidal

Protein kinase A phosphorylates ______ ______ ____ _________

transcription factor CREB protein

PKA can directly phosphorylate target proteins OR...

it can phosphorylate transcription factor CREB protein

CREB

protein that can switch genes on/off with memory and connection of memories

- binds to CRE

- once phosphorylated, will recruit CBP

- has a role in development in neurons (formation of long-term memory, survival), and many other organs

What does CBP activate?

transcription of target genes

A change in cAMP concentration can alter ____ ________.

gene transcription

steps of gene transcription w change in cAMP concentration

GPCR activates G protein

G protein activates adenylyl cyclase

increase in cAMP concentration

activation of PKA

phosphorylation and activation of CREB

CREB binds to CRE and recruits CBP promoter

transcription activation

What can be a function of CBP if you know that it activates transcription?

•A. Histone acetyltransferase (HAT)

•B. Histone deacetylase (HDAC)

•C. Histone methyltransferase

A. Histone acetyltransferase (HAT)

Turning on the pathway immediately turns it off: PKA activates cAMP phosphodiesterase, which ______ _____.

lowers cAMP

- mechanism for making a response brief

G-proteins exist in many forms

Gi = ?

Gs = ?

Gq = ?

Gi = inhibitory G-protein, inhibits adenylyl cyclase

Gs = stimulatory G-protein, stimulates adenylyl cyclase

Gq = atypical G-protein, couples to other effector molecules (for example, opens or closes ion channels)

GPCR can activate protein kinase C through ______________.

phosphoinositides

Phosphatidylinositol (PI) is a what charged phospholipid and sits at the what of the plasma membrane

negatively charged

sits at the cytosolic part of the plasma membrane

Phosphoinositides can be phosphorylated at positions _, _, and _ to form phosphoinositides

3,4, and 5

some g proteins activate _____ phospholipid signaling pathway

Inositol

Phospholipase cleaves....

PIP2

Inositol 1,4,5-triphosphate IP3

•Water-soluble small intracellular mediator

•Opens IP3-gated Ca2+-release channels in endoplasmic reticulum

•Increase of Ca2+ conc. in cytosol

•Ca2+ influences activity of some proteins

•Response terminated by lipid phosphatases

IP3 --> IP2, or lipid kinases IP3 --> IP4. Ca2+ is pumped out of the cell

Which of the following is water-soluble?

•A. PIP2

•B. PIP3

•C. IP3

•D. All of the above

•E. None of the above

C. IP3

Diacylglycerol and Ca2+ activate...

protein kinase C (PKC)

activation of PLCb by GPCRs leads to an increase in ____________ ____ and activation of PKC

intracellular Ca2+

IP3 binds to and activates IP3 receptor, a ______-_____ Ca2+ channel on intracellular membranes release of Ca2+ from intracellular stores

ligand-gated

roles of PKC

-contraction of smooth muscle

-Vasoconstriction

-secretion (salivary gland, sweat gland, etc.)

- other functions

Ca2+ functions as a ubiquitous intracellular mediator

- Many extracellular signals increase Ca2+ concentration

- Ca2+ concentration is normally low in the ______, but high in the extracellular fluid and in the lumen of endoplasmic reticulum

- concentration is kept low by pumps in the plasma membrane, ER, and mitochondria, and by Ca2+ binding proteins

- signals can transiently open the channels in plasma membrane or ER

- high Ca2+ concentrations activate Ca2+ responsive proteins

cytosol

Calmodulin

- most important protein, which helps to relay (1)___ signal

- found in all (2)______ cells

- constitute up to 1% of cell protein mass

- intracellular Ca2+ receptor

- highly conserved

- does NOT have enzymatic activity; acts by binding to and activating other proteins

1. Ca2+

2. eukaryotic

Calmodulin has ___ Ca2+ binding sites

- Ca2+ binding induces conformational change

4

Calmodulin goes through conformational change upon binding _______

calcium

Calmodulin activates other proteins by_____

•A. Inducing conformational change

•B. Phosphorylation

•C. Dephosphorylation

A. Inducing conformational change

Calmodulin activates:

plasma membrane Ca2+ pumps, calmodulin-dependent kinases, some gene regulatory proteins

the role of CaMKII

- enriched in nervous system, can constitute up to 2% of the cell protein mass in some braincells

- highly concentrated at synapses

- CaMKII can stay active for a long time after Ca2+ impulse and serve as a memory devise

- mice which lack a brain-specific form of CAMKs have defects in their ability to remember object's locations

CaMKII strengthens __________, which accounts for long term memory

synapses

which neurotransmitter is one of the main in the mammalian central nervous system?

glutamate

CaMKII helps in addition of glutamate receptors to the membrane of ________ neurons

postsynaptic

Ca2+/Calmodulin-Dependent Protein Kinases Mediate Many Responses to Ca2+ Signals

steps:

A domain pops out of CaMK II kinase complex

Calmodulin binds (1)____

This enables calmodulin to bind to CaMK II domain and activate it by promoting a conformational change

This results in a (2)________ _________ ________.

When another domain pops out, it gets activated as well, and then CaMKII domains (3) ___________ each other

Phosphorylates CaMK stays phosphorylated and active even after calmodulin dissociates

1. Ca2+

2. partially active kinase

3. phosphorylate

Q: Which of the following explains long-term memory?

•A. CaMKII stays activated by calmodulin

•B. CaMKII is autophosphorylated

B. CaMKII is autophosphorylated

The same signaling molecule, _________, can bind to GPCR or an ion channel receptor

acetylcholine

Nicotinic acetylcholine receptors is an ___ ____ __________

can also be opened by nicotine, which causes its addictive effects

ion channel receptor

signal transduction pathway for rods

•Rods are responsible for night vision

•When rhodopsin absorbs a photon, its conformation changes

• Then α subunit of G protein activates cGMP phosphodiesterase. cGMP concentration falls

•cGMP-sensitive channels close.

•This causes hyperpolarization of the neuron

•This inhibits release of glutamate

•Glutamate inhibits the next neuron in the chain (bipolar cell)

•Bipolar cell looses its inhibition and transmits the signal

_____ and _____ are based on GPCRs that regulate ion channels through cAMP/cGMP

smell & vision

A possible role of cAMP is...

•A. Activation of a kinase

•B. Opening an ion channel

•C. Both A and B

•C. Both A and B

T/F: Glutamate is always an inhibitory neurotransmitter

false

Rod bipolar cells are inhibited by...

glutamate

_____ decreases the glutamate release and so activates the bipolar cells

light

Dark vs. light ?

Dark:

GPCR rhodopsin inactive

High level of cGMP

Neuron depolarized

High rate of neurotransmitter glutamate release

Glutamate inhibits bipolar cells

No signal

Light:

Stimulates GPCR

Low level of cGMP

Na-channels close

Low rate of glutamate release

Bipolar cell gets activated

Signal gets transmitted to the brain

Which of the following is mostly based on cAMP increase?

smell

vision

smell

comparison of the light and the smell signal transduction pathways

light:

•Rhodopsin GPCRs

•Activation leads to decrease in cGMP

•Na-channel closes

•Glutamate level decreases

•Intermediate neurons are activated

•Signal is transmitted

smell:

•Olfactory GPCRs

•Activation leads to increase in cAMP

•Na-channel opens

• Neural cell transmits the signal to the brain

Gas ____ is a signal molecule in animals and plans

NO (nitrous oxide)

NO (g)

- relaxes smooth muscles in animals

- can lead to dilation of blood vessels

- can diffuse across the membrane in and out of cells

Nerves release what neurotransmitter ___?

& how do the cells respond?

acetylcholine

endothelial cell responds by releasing NO

NO relaxes smooth muscle cells

blood vessel dilates

NO(g) only acts _______ & why

locally

- lifetime is 5-10 seconds

- oxygen and water eventually convert it into nitrites and nitrates

signaling molecule

cyclic GMP

signaling molecule

relaxes smooth muscles

- produced from GTP

what catalyzes the conversion of cGMP to GMP?

phosphodiesterase

Which enzyme does Viagra block?

•A. It blocks guanylyl cyclase that makes cGMP, which is a signal to relax a smooth muscle

•B. It blocks cGMP phosphodiesterase

•C. It blocks GPCR

•B. It blocks cGMP phosphodiesterase

Mechanism of relaxation of smooth muscle

NO is produced in cells from amino acid arginine by NO synthase (NOS)

NO binds to active site of guanylyl cyclase, activating it to produce other intracellular signaling molecule cyclic GMP

cGMP relaxes smooth muscles and helps blood vessels dilate

The drug nitroglycerine is converted into NO in the body.

- It is used to prevent heart attack

NO synthase in smooth muscle relaxation pathway is in _____

•A. Smooth muscle cells

•B. Nerve cells

•C. Epithelial cells

B. Nerve cells