cell signalling 3

Question 1

cAMP as second messenger

cAMP acts as a Second Messenger for several regulatory molecules.

Protein Kinase A (PKA) → cAMP binds to ? site and activates PKA:

• activates enzymes involved in:
   fat ? and
   ? synthesis
• can also move into the nucleus, where it phosphorylates CREB (cAMP response element binding protein
   This alters the ? of specific genes regulated by [cAMP] in the cell
   By binding to ? on the DNA and either stimulating or inhibiting their ?

Answer 1

cAMP as second messenger

cAMP acts as a Second Messenger for several regulatory molecules.

Protein Kinase A (PKA) → cAMP binds to regulatory site and activates PKA:

• activates enzymes involved in:
   fat mobilization and
   cortisol synthesis
• can also move into the nucleus, where it phosphorylates CREB (cAMP response element binding protein
   This alters the expression of specific genes regulated by [cAMP] in the cell
   By binding to specific genes on the DNA and either stimulating or inhibiting their transcription

Question 2

FYI

Activation of enzymes involved in fat mobilization

Glucagon (first or second? messenger) → Adipocytes -> Gs activation of ? -> increase [?] -> stimulates PKA -> PKA activates enzymes involved in ? mobilization (hormone sensitive lipase)

(recall: Glucagon - hormone of starvation

To make more glucose available for our body)

Answer 2

Activation of enzymes involved in fat mobilization

Glucagon (first messenger) → Adipocytes -> Gs activation of AC -> increase [cAMP] -> stimulates PKA -> PKA activates enzymes involved in fat mobilization (hormone-sensitive lipase)

(thus, glucagon is the first messenger that will bind to GPCR stimulatory pathway.

Gs = G alpha subunit of Gs stimulating AC

Right. And what glycerol can do here? Go into the gluconeogenesis pathway to provide glucose for the body and then the free fatty acids can do what? Provide energy through the beta oxidation metabolic pathway, remember?
So that’s how we are wrapping up everything we’ve been discussing so far.
talking about small details, How the glucagon is binding to these receptors and triggering all these responses in the body)

Question 3

IMP! -> Higher the [cAMP], higher the activated ?

PKA can also go into the ? of cell and bind to cAMP response element binding protein or ? protein for short.

1. so first messenger binding to ? coupled receptor, increasing ? thus activating pKa in the ?
2. PKA will then go to the ? where they phosphorylate the CREB gene regulatory protein -> this will stimulate the ? of genes.
3. That’s another way this cyclicAMP pathway can work on cellular response and in this case we are synthesizing ? (other enzymes)

The signal pathway controls many processes in cells, ranging from hormone synthesis in ? cells to the production of proteins needed for long term ? in the brain.

Answer 3

IMP! -> Higher the [cAMP], higher the activated PKA

PKA can also go into the nucleus of cell and bind to cAMP response element binding protein or CREB protein for short.

1. so first messenger binding to GPCR coupled receptor, increasing cyclicAMP thus activating pKa in the cytosol
2. PKA i.e., the released catalytic subunits will then go to the NUCLEUS where they phophorylate the CREB gene regulatory protein -> this will stimulate the TRANSCRIPTION of genes.
3. That’s another way this cyclicAMP pathway can work on cellular response and in this case we are synthesizing proteins (other enzymes)

The signal pathway controls many processes in cells, ranging from hormone synthesis in endocrine cells to the production of proteins needed for long term memory in the brain.

(note: GPCR complex is basically the GPCR along with the a, b and gamma subunits with the GDP molecule attached to a subunit - the 1st whole thing)

Question 4

GPCRs PATHWAYS CAN REGULATE ION CHANNELS

G proteins do not act exclusively by regulating the activity of enzymes

They can directly activate or inactivate ? channels in the plasma membrane – through the action of the βꝩ subunits

Ligand-gated ion channel: Nicotinic-ACh receptors
- postsynaptic membrane of:
1. all ? ganglia
2. all ? junctions
3. some ? pathways

GPCR: Muscarinic ACh receptors
1. Produces ? (relax) nerve effects in the heart, smooth muscles, and glands
2. G-protein coupled ? (receptors influence ion channels by means of G proteins)

• Alter the ? permeability and ? excitability
• Ex: Acetylcholine released by the vagus nerve ? heart rate and stimulates smooth muscle ?

What is the other classification for Nicotonic-ACh receptors? -> ionotropic

Answer 4

GPCRs PATHWAYS CAN REGULATE ION CHANNELS

G proteins do not act exclusively by regulating the activity of enzymes

They can directly activate or inactivate ion channels in the plasma membrane – through the action of the βꝩ subunits

Ligand-gated ion channel:
Nicotinic-ACh receptors - postsynaptic membrane of:
1. all autonomic ganglia
2. all neuromuscular junctions
3. some CNS pathways

GPCR: Muscarinic ACh receptors
1. Produces parasympathetic (relax) nerve effects in the heart, smooth muscles, and glands
2. G-protein coupled receptors (receptors influence ion channels by means of G proteins)

Gi inhibits Adenylyl cyclase while βγ subunits bind to K channels, that will open this channel making depolarization of the cells more difficult

• Alter the ion permeability and electrical excitability
• Ex: Acetylcholine released by the vagus nerve reduces heart rate and stimulates smooth muscle contraction

notes:
(So the alpha subunit of this gpcr complex - Ach ligand bound to it, inhibits AC and will not produce cyclic AMP.

more K inside usually but if channel open then K goes out, so towards the [gradient] so making inside more (-) thus HYPERPOLARIZATION so slows down the heart rate here so it’s an inhibitory effect because of the action of the alpha subunit.

No cyclic amp, but the beta gamma subunit will bind direct to this potassium channels, making this cell hyper polarized and is slowing down everything

if we are talking about these smooth muscle of the digestive tract, for example, the same muscarinic receptors will have a different response will trigger diff effect as its in smooth muscle.

So here the better gamma subunit will bind to this potassium channel, but instead open it, it will keep it CLOSED so depolarization occurs easier here

resulting in contractility of muscle e.g. increasing peristaltic movements.

THUS THATS THE WAY BETA-GAMMA SUBUNITS CAN ACT oN CHANNELS, such as on K+ channels.

(What is the other classification for Nicotonic-ACh receptors? -> ionotropic

both muscarinic and nicotonic-ach repceptors will bing to acetylcholine but they are v diff. structurally and act diff.

Question 5

TIME TO SWITCH UR BRAIN! : )

MSG TRANSDUCTION - PHOSPHATIDYLINOSITOL (PIP2) PATHWAY

DAG, IP3 AND CA2+ Have related roles as 2nd messengers

-> another broad class of GPCRs are coupled through * ? * protein to a * ? * (PLC)
- the enzyme PLC is specific for a membrane phospholipid: PIP2 (phosphatidylinositol 4,5-bisphosphate)

(So we are talking now about the G protein coupled receptor, which is bound to the Q protein and it will act through the effector enzyme Phospholipase C

So we don’t have cyclic AMP as second messenger in this pathway.

PIPII v imp for cellular communication pathway.

PIC: g protein coupled receptors, the GQ protein which will again have alpha, beta, gamma, subunit.
the alpha subunit exchanges GDP to GTP and INSTEAD ACTIVATING the AC, it will activate the PHOSPHOLIPASE C which will break down PLs

The molecular shape in the middle, is the two hydrocarbon chains in the polar head ( structure of the phospholipid)

so this phospholipase will cut the head of this PL and it will leave the hydrophobic tail in the membrane which will diffuse in the cytosol of the cell

and the diacylglycerol with the two hydrocarbon tails here, are lipid like and will stay in the PM.

Answer 5

-> another broad class of GPCRs are coupled through * Gq * protein to a * PHOSPHOLIPASE C* (PLC)
- the enzyme PLC is specific for a membrane phospholipid: PIP2 (phosphatidylinositol 4,5-bisphosphate)

Question 6

So what is happening here? Ligand binding to the receptor.

The alpha subunit is activated so change GDP to GTP which binds to the ?

phospholipase C will then break the phosphatidyl inositol 2 into powerful second messengers: ? and ?

since IP3 is ?, its free in the cytosol and then comes and binds to ? ligand-gated ion channel located in ER.

(recall: ER and sarcoplasmic reticulum store lots of calcium So then this is a way that this IP 3 guy here can bind to this calcium channel and open it up so we have calcium coming to cytosol of cell and CALCIUM will be SECOND messenger as well)

calcium now in cytosol and then it binds to the ? and it will activate the protein kinase C (NOT protein kinase “A”)

Answer 6

So what is happening here? Ligand binding to the receptor.

The alpha subunit is activated so change GDP to GTP which binds to the phospholipase C

phospholipase C will then break the phosphatidyl inositol 2 into IP3 and DAG

since IP3 is hydrophilic, its free in the cytosol and then comes and binds to calcium ligand-gated ion channel located in ER.

(recall: ER and sarcoplasmic reticulum store lots of calcium So then this is a way that this IP 3 guy here can bind to this calcium channel and open it up so we have calcium coming to cytosol of cell and CALCIUM will be SECOND messenger as well)

calcium now in cytosol and then it binds to the DAG and it will activate the protein kinase C (NOT protein kinase “A”)

Question 7

phosphatidylinositol (PIP 2) pathway

1. Signal hormone binding to the specific receptorA
2. Activates ? protein
3. Which activates the PIP2-specific PLC
4. This activation catalyzes the production of two powerful second messengers: ? and ?
5. IP3 is hydrophilic, diffuses to ER and binds to specific IP3-gated Ca2+ channels causing them to open and release stored Ca2+ to the cytosol
6. ↑ [Ca2+ ] in combination with DAG activates Protein Kinase C or A?
7. Many enzymes activated by PKC affect ? proteins, ? proteins, and other enzymes (cellular response)

Answer 7

1. Signal hormone binding to the specific receptorA
2. Activates Gq protein
3. Which activates the PIP2-specific PLC
4. This activation catalyzes the production of two powerful second messengers: diacylglycerol (DAG) and inositol 1,4,5- trisphosphate (IP3)
5. IP3 is hydrophilic, diffuses to ER and binds to specific IP3-gated Ca2+ channels causing them to open and release stored Ca2+ to the cytosol
6. ↑ [Ca2+ ] in combination with DAG activates Protein Kinase C (PKC)
7. Many enzymes activated by PKC affect cytoskeleton proteins, nuclear proteins, and other enzymes (cellular response)

Question 7

Ca++ RELEASE:

 Can also be caused by ?
pathway

 via activation of PKA and cell
?

(not only PIP2 but also the cyclic AMP pathway can also release calcium into the cytosol.
- protein kinase “A” can trigger the opening of calcium channels in the cell surface membrane and extracellular calcium can come inside of cell and act as 2nd messenger.
- And it can also stimulate the release of more calcium for the sarcoplasmic reti. or the endoplasmic reticulum.
THUS, diff ways that signal transduction pathway can release calcium as a second messenger)

Answer 7

Ca++ RELEASE:

 Can also be caused by cAMP
pathway

 via activation of PKA and cell
Ca++ channels

(not only PIP2 but also the cyclic AMP pathway can also release calcium into the cytosol.
- protein kinase “A” can trigger the opening of calcium channels in the cell surface membrane and extracellular calcium can come inside of cell and act as 2nd messenger.
- And it can also stimulate the release of more calcium for the sarcoplasmic reti. or the endoplasmic reticulum.
THUS, diff ways that signal transduction pathway can release calcium as a second messenger)

until here for block 3!!