61 | Signal Transduction

what is the effector in the epinephrine pathway

adenylate cyclase (AC)

What are the 3 main steps of signal transduction?

Reception; Transduction; Cellular response.\n\n

What happens during reception?

A ligand (signal molecule) binds to a specific receptor.\n\n

What happens during transduction?

The signal is relayed and amplified inside the cell via intermediates (e.g., G proteins, second messengers).\n\n

What happens during the cellular response?

A functional change occurs (e.g., enzyme activation, gene expression, metabolism change).\n\n

What is a signal (ligand)?

A molecule that carries information (e.g., hormone like insulin or epinephrine).\n\n

What is a receptor?

A protein that binds the ligand and initiates signaling.\n\n

What is a transducer?

A molecule that relays the signal inside the cell (e.g., G protein).\n\n

What is an effector?

A molecule (often an enzyme) that produces the cellular response.\n\n

What is a second messenger?

A small intracellular molecule that amplifies the signal (e.g., cAMP).\n\n

What are the 4 classes of extracellular signals?

Hormones; Neurotransmitters; Pheromones; Growth factors.\n\n

Which signals act over long distances?

Hormones (via bloodstream).\n\n

Which signals act locally and quickly?

Neurotransmitters.\n\n

What are pheromones?

Signals released by one organism that affect another organism.\n\n

What are the 3 types of hormones?

• Peptides (insulin)

• Steroids (estrogen)

• Amino acid derivatives (epinephrine)

What is a key feature of hormones?

They travel through the bloodstream to distant target cells.\n\n

What does insulin do?

Promotes glucose uptake into cells when blood glucose is high.\n\n

What does glucagon do?

Promotes glycogen breakdown and glucose production when blood glucose is low.\n\n

What does epinephrine do?

Stimulates energy production (ATP) for muscle activity.\n\n

What type of receptor is the beta-adrenergic receptor?

G protein-coupled receptor (GPCR).\n\n

What activates a G protein?

Exchange of GDP for GTP.\n\n

What is the inactive state of a G protein?

GDP-bound.\n\n

What is the active state of a G protein?

GTP-bound.\n\n

What enzyme does the G protein activate?

Adenylate cyclase.\n\n

What does adenylate cyclase do?

Converts ATP to cAMP.\n\n

What is cAMP?

A second messenger.\n\n

What does cAMP activate?

Protein kinase A (PKA).\n\n

What does PKA do?

Phosphorylates downstream proteins.\n\n

What is the final outcome of the epinephrine pathway?

Glycogen breakdown, glucose release, and ATP production.\n\n

What is signal amplification?

One signal molecule triggers many downstream molecules, producing a large response.\n\n

Why is amplification important?

It allows a small signal to create a large cellular effect.\n\n

What activates phosphorylase kinase?

Phosphorylation by protein kinase A (PKA).\n\n

What activates glycogen phosphorylase?

Phosphorylation by phosphorylase kinase.\n\n

Active vs inactive glycogen phosphorylase?

a = active (phosphorylated); b = inactive (dephosphorylated).\n\n

What type of receptor is the insulin receptor?

Receptor tyrosine kinase (RTK).\n\n

What happens when insulin binds its receptor?

Activates tyrosine kinase activity and initiates a phosphorylation cascade.\n\n

What second messenger is produced in insulin signaling?

PIP3.\n\n

What is the final effect of insulin signaling?

GLUT4 moves to the membrane, increasing glucose uptake.\n\n

GPCR vs RTK (main difference)?

GPCR uses G proteins and cAMP; RTK uses phosphorylation cascades (kinases).\n\n

What do all signaling pathways have in common?

Signal binds receptor, signal is transduced, and a cellular response is produced.\n\n

overall epinephrine pathway

• epinphrine binds beta adrengeric receptor

• this activates trimeric g protein

• this activates adenylate cyclase

• tihs activated cAMP

• cAMP binds protein kinase a to activate it

• this activates phosphorylase kinase b

• this activates glycogen phosphorylase

  • glycogen phosphorylase b → inactive bc dephosphorylated

  • glycogen phosphorylase a → active bc phosphorylated

• this catalyses breakdown of glycogen

• this releases glucose-1-phosphate for degredation + ATP synthesis

• this supports muscle contraction which is why epinephrine was released to do

overall insulin pathway

• insulin binds to its tyrosine kinase insulin receptor

• its binding activates tyrosine kinase activity

• activates a cascade where PIP3 (secondary messanger) is synthesized

• at the end of this cascade, GLUT4 proteins are relocalized to the membrane

• they are hwat uptakes glucose