Biochemistry test 3 fc for worksheets

In the cAMP and PKA pathway, what does epinephrine bind to?

the Beta-Adrenergic receptor

In the cAMP and PKA pathway, when the receptor binding promotes a nucleotide exchange on Gαs, what leaves and what binds?

GDP leaves and GTP binds

In the cAMP and PKA pathway, what is activated when Gαs-GTP separates from Gβγ?

Adenylyl cyclase

In the cAMP and PKA pathway, what is ATP converted to?

cAMP

In the cAMP and PKA pathway, what PKA subunits does cAMP bind to?

R chains

In the cAMP and PKA pathway, when cAMP binds to PKA subunits, what active subunits are released?

C chains

In the cAMP and PKA pathway, what targets proteins on Ser/Thr residues?

Protein kinase A

In the cAMP and PKA pathway, what are the primary and secondary messengers?

the primary messenger is epinephrine and the secondary messenger is cAMP

In the cAMP and PKA pathway, what are the amplification steps?

• One activated GPCR can activate multiple G proteins.

• Each activated Gαs protein can activate adenylyl cyclase.

• Each adenylyl cyclase produces many cAMP molecules from ATP.

• cAMP activates multiple PKA molecules.

• Each activated PKA can phosphorylate many target proteins.

In the phosphoinositide pathway, what does epinephrine bind to?

Alpha-adrenergic receptors

In the phosphoinositide pathway, what does the Gαq exchange?

GDP for GTP.

In the phosphoinositide pathway, on Gαq, when GDP is exchanged for GTP, what is activated?

Phospholipase C

In the phosphoinositide pathway, what membrane does phospholipase C enzyme cleave?

PIP2, forming IP3 adn DAG

In the phosphoinositide pathway, after membrane cleavage, what diffuses through the cytosol?

IP3

In the phosphoinositide pathway, after membrane cleavage, what remains in the cytoplasm?

DAG

In the phosphoinositide pathway, what does IP3in the cytosol do?

Opens channels on the ER, releasing Ca2+ into the cytosol.

In the phosphoinositide pathway, what does Ca2+ bind to?

CaM, forming a Ca2+-CaM complex, which activates CaM kinase and other targets.

In the phosphoinositide pathway, what does DAGin the plasma membrane do?

Allows doe DAG and Ca2+ to activate PKC, which phosphorylates targets.

In the phosphoinositide pathway, what are the three second messengers?

IP3, DAG, and Ca2+

In the phosphoinositide pathway, why does IP3 binding to its channel increase cytosolic Ca2+?

Because there are specific IP3-gated Ca2+ channels, which allows Ca2+ to flow through rapidly.

In the phosphoinositide pathway, how can Ca2+ activate targets through the two different routes?

Ca2+ binds to CaM, which forms the Ca2+-CaM complex, but it also works with DAG to recruit PKC, and binds directly with targets.

What are the differences in the Gα subtype in the cAMP and the phosphoinositide pathways?

In the cAMP cycle, Gαs attaches to adenylate cyclase, concverting ATP into cAMP and activating PKA. In the phosphoinositide pathway, Gαq binds to phospholipase C, which cleaves PIP2, leaving IP3 and DAG.

What are the differences in the effector enzyme in the cAMP and the phosphoinositide pathways?

In the cAMP pathway, the effector enzyme is adenylate cyclase, and in the phosphoinositide pathway, the effector enzyme is phospholipase C.

What are the differences in the second messengers in the cAMP and the phosphoinositide pathways?

In the cAMP pathway, cAMP is the second messenger and in the phosphoinositide pathway, IP3, DAG, and Ca2+ are the second messengers.

What are the differences in the protein kinase activated in the cAMP and the phosphoinositide pathways?

In the cAMP pathway, PKA is activated and in the phosphoinositide pathway, PKC is activated.

What are the differences in the membrane-associated messenger in the cAMP and the phosphoinositide pathways?

In the cAMP pathway, there is no membrane associated messenger, and the phosphoinositide pathway, DAG is the membrane-associated messenger.

What is the G protein reset reaction?

When Gα subunits hydrolyze GTP, creating GDP and Pi.

What happens after the G protein reset reaction?

the GDP-bound form of Gα reassociates with Gby to reform the inactive heterodimer

How do receptor phosphorylation and β-arrestin reduce signaling?

G-protein receptor kinases phosphorylate Ser and Thr residues in receptors, then β-arrestin bind to and block the receptor’s ability to activate G proteins.

What would happen to cAMP signaling if Gαs can bind GTP, but cannot hydrolyze it?

Without hydrolysis, the Gαs would not reset, so the signal would continuously activate because the Gαs would stimulate adenylyl cyclase, which would would keep producing cAMP and PKA would remain activated, causing prolonged downstream signaling.

What would happen to cytosolic Ca2+ release if the IP3-gated ER channel is blocked?

Cytosolic Ca²⁺ release would decrease or be blocked because IP₃ could no longer open the ER Ca²⁺ channels. Ca²⁺ would remain stored in the ER, reducing Ca²⁺-dependent signaling.

What would happen to PKC activation if the IP3-gated ER channel is blocked?

PKC activation would decrease because blocking the IP₃-gated ER channel prevents Ca²⁺ release into the cytosol. Since PKC requires both Ca²⁺ and DAG for full activation, less Ca²⁺ would result in reduced PKC activation.

How can two cells respond differently if epinephrine activates both pathways?

Two cells can respond differently because they have different receptors, signaling proteins, and target protein

In insulin receptor signaling, what is the insulin-responsive glucose transporter?

GLUT4

In insulin receptor signaling, after insulin binds it’s preformed dimeric receptor, what happens to the receptor?

The conformation of the extracellular domains change from a V shape to a T shapes, causing the protein kinase domains to come together upon insulin binding.

In insulin receptor signaling, what residues does receptor kinase domains cross-phorylate?

Tyrosine residues, activating the receptors.

In insulin receptor signaling, what do the active receptors phosphorylate?

The tyr in the sequence Tyr-X-X-Met in insulin receptor substrates (IRS).

In insulin receptor signaling, what does the cross-phorylation of Tyr residues do?

Increases tyrosine kinase activity.

In insulin receptor signaling, what do IRS adaptor proteins do?

Recruit PI3K

In insulin receptor signaling, what does PI3K phosphorylate?

Membrane PIP2 to produce PIP3.

In insulin receptor signaling, what does PIP3 do?

Recruits PDK1 and PKB to the membrane.

In insulin receptor signaling, what does PDK1 do?

Helps activate PKB, making Akt.

In insulin receptor signaling, what does active PKB do?

Promotes movement of glucose transporters to the cell surface.

In insulin receptor signaling, what do muscle and fat cells show increased concentrations of in the blood.

Muscle and fat cells increase the number of GLUT4 glucose transporters on their plasma membranes, increasing glucose uptake from the blood.

In insulin receptor signaling, what does a receptor tyrosine kinase transfer? What molecule supplies it?

A phosphoryl group from ATP to tyrosine residues on target proteins.

Explain one amplification step in insulin signaling.

Activated receptors can phosphorylate multiple IRS molecules, and activated enzymes further amplify the signal.

In the EGF receptor signaling, what occurs after EGF binds to its receptors?

the receptors dimerize, activating their tyrosine kinase domains. They then cross-phosphorylate tyrosine residues on each other.

In the EGF receptor signaling, where are receptor tails phosphorylated?

On tyrosine residues of the intracellular (cytoplasmic) receptor tails. the receptor is then active.

In the EGF receptor signaling, what adator proteins binds to the receptor?

Grb2

In the EGF receptor signaling, what does Grb2 do?

recruits the GEF Sos

In the EGF receptor signaling, what does SOS promote?

Nucleotide exchange on Ras.

In the EGF receptor signaling, after nucleotide exchange on Ras, what leaves Ras and what binds to Ras?

GDP leaves and GTP binds

In the EGF receptor signaling, what does Ras-GTP activate?

Raf

In the EGF receptor signaling, what does Raf do?

phosphorylates MEK

In the EGF receptor signaling, what does MEK do?

Phosphorylates and activates ERKs

In the EGF receptor signaling, what does activated ERK do?

Phosphorylates transcription factors.

In the EGF receptor signaling, what do changes in gene expression do?

Supports cell growth.

In the EGF receptor signaling, what does SOS do to activate Ras? Does it phosphorylate Ras?

Opens the nucleotide-binding pocket of Ras, it does not phosphorylate.

Write the kinase cascade downstream of Ras in order in EGF receptor signaling.

Ras → Raf → MEK → ERK → transcription factors and other protein kinases.

In the EGF receptor signaling, how can activation of ERK change gene expression?

They phosphorylate transcription factors in the nucleus and other protein kinases

What is the receptor class in the insulin pathway? The EGF pathway?

RTK for both

What is the receptor before ligand binding in Insulin pathway? The EGF pathway?

The insulin receptor is a preformed dimer, while the EGF receptor exists as a monomer.

What is the adaptor protein in insulin pathway? The EGF pathway?

The insulin pathway uses IRS proteins, while the EGF pathway uses Grb2

What is the key lipid signal and GTP switch in the Insulin Pathway? The EDF Pathway?

The insulin pathway uses PIP₃ as its key lipid signal and does not use a Ras GTP switch, while the EGF pathway uses Ras-GTP as its GTP switch and does not use PIP₃ as its key lipid signal.

What is the downstream protein kinase in the insulin pathway? The EGF pathway?

The insulin pathway uses Akt (PKB), while the EGF pathway uses ERK.

What is the main response from the Insulin pathway? The EGF pathway?

The insulin pathway increases glucose uptake and storage, while the EGF pathway promotes cell growth.

Name a protein target and a lipid target of phosphatase in insulin signaling.

Protein target: Akt (dephosphorylated by protein phosphatases).

Lipid target: PIP₃ (dephosphorylated back to PIP₂ by PTEN).

What is the Ras reset reaction?

Ras-GTP + H₂O → Ras-GDP + Pi

What do GAPs do?

GAPs accelerate GTP hydrolysis, switching Ras from its active GTP-bound state to its inactive GDP-bound state.

What would happen to PIP3 formation if PI3K is inhibited?

PIP₃ formation would decrease or stop because PI3K can no longer phosphorylate PIP₂ to produce PIP₃.

What would happen to insulin-stimulated glucose uptake if PI3K is inhibited?

Insulin-stimulated glucose uptake would decrease because reduced PIP₃ formation prevents Akt activation and GLUT4 translocation to the plasma membrane.

What would happen to downstream kinase activity if Ras cannot efficiently hydrolyze GTP?

Downstream kinase activity would remain elevated because Ras stays GTP-bound and active, continuously activating the Raf → MEK → ERK cascade.

In which cellular compartment does glycolysis occur?

Cytosol

What is the starting molecule of glycolysis?

glucose

What are the final products of glycolysis per 1 glucose?

two pyruvate

What is the net ATP gain from glycolysis?

two ATP

What is the role of NAD+ in glycolysis?

Oxidize aldehyde to a carboxylic acid

What are the three irreversible steps in glycolysis?

Step 1 (glucose to glucose 6-phosphate), step 3 (fructose 6-phosphate to fructose 1,6-biphosphate), and the final step (phosphoenolpyruvate to pyruvate)

In the Glycolysis pathway, what does Glucose become?

Glucose-6 phosphate by hexokinase

In the Glycolysis pathway, what does Glucose-6 phosphate become?

Fructose-6-phosphate by PFI

In the Glycolysis pathway, what does Fructose-6-phosphate become?

Fructose 1,6-biphosphate by PFK

In the Glycolysis pathway, what does Fructose 1,6-biphosphate become?

Dihydroxyacetone phosphate and glyceraldehyde 3-phosphate by aldolase. which then can become each other with TPI

In the Glycolysis pathway, what does glyceraldehyde 3-phosphate become?

1,3-biphosphoglycerate by GAPDH

In the Glycolysis pathway, what does 1,3-biphosphoglycerate become?

3-phosphoglycerate by PGK

In the Glycolysis pathway, what does 3-phosphoglycerate become?

2-phosphoglycerate by PGM

In the Glycolysis pathway, what does 2-phosphoglycerate become?

phosphoenolpyruvate by enolase

In the Glycolysis pathway, what does phosphoenolpyruvate become?

pyruvate by pyruvate kinase

Which enzyme sets the pace of glycolysis?

PFK

What molecule activates phosphofructokinase-1 (PFK-1)?

Fructose 2,6 biphosphate

What molecules inhibit PFK-1?

ATP, citrate and low pH

Why is hexokinase inhibited by glucose-6-phosphate?

Glucose-6-phosphate inhibits hexokinase through feedback inhibition, signaling that enough glucose has already been phosphorylated and preventing unnecessary glucose trapping in the cell.

At which steps is ATP produced?

Step 7, Phosphoglycerate kinase, and Step 10 Pyruvate kinase

At which step is NADH produced?

Step 6, Glyceraldehyde-3-phosphate (G3P) to 1,3 bisphosphoglycerate (1,3-BPG)

What happens to pyruvate under anaerobic conditions?

Pyruvate is converted to lactate by lactate dehydrogenase, regenerating NAD⁺ so glycolysis can continue producing ATP.

Why is the conversion of PEP to pyruvate highly exergonic?

Because PEP has a high phosphoryl-transfer potential because the phosphoryl group traps the molecule in its unstable enol form

Explain substrate-level phosphorylation.

Substrate-level phosphorylation is the direct transfer of a phosphate group from a high-energy substrate molecule to ADP, producing ATP. It does not require oxygen or the electron transport chain.

What is an example of substrate-level phosphorylation?

During glycolysis, phosphoenolpyruvate (PEP) transfers its phosphate group to ADP through the enzyme pyruvate kinase, producing ATP and pyruvate.

What are the two major cellular roles of glycolysis?

It degrades glucose to generate ATP and it provides building blocks for synthetic reactions.

What enzymes are involved in each step of the irreversible control steps in glycolysis?

Hexokinase, phosphofructokinase and pyruvate kinase

What are the substrates and major products of each step of the irreversible control steps in glycolysis?

glucose to glucose 6-phosphate by hexokinase, fructose 6-phosphate to fructose 1,6-biphosphate by phosphofructokinase, and phosphoenolpyruvate to pyruvate by pyruvate kinase