Module 6

What is signal transduction?

Process where cells convert an extracellular signal into a cellular response.

What are extracellular signals?

Messages that originate outside the cell and bind to receptors.

What determines whether a cell responds to a signal?

Presence of the correct receptor.

What are the three steps of signal transduction?

Reception → Transduction → Cellular response

What happens during reception?

Ligand binds to a receptor and activates it.

What happens during transduction?

Signal is relayed and amplified inside the cell.

What happens during the cellular response?

Cell carries out a specific action (e.g., enzyme activation, gene expression).

What are the four classes of extracellular messengers?

Hormones, neurotransmitters, pheromones, growth factors

How do hormones act?

Travel long distances through the bloodstream.

How do neurotransmitters act?

Act locally over short distances.

What are pheromones?

Signals that act between organisms —> secreted by one to act on another

What do growth factors regulate?

Cell growth and development.

What are the three main types of hormones?

Peptides, steroids, amino acid derivatives

What is a key feature of steroid hormones?

They can cross the cell membrane.

What is a ligand?

A signaling molecule that binds to a receptor.

Where can receptors be located?

Cell membrane or inside the cell.

What does insulin do?

Promotes glucose uptake and lowers blood glucose.

What does glucagon do?

Stimulates glycogen breakdown and increases blood glucose.

What does epinephrine do?

Increases energy production (ATP), especially during stress/exercise.

What type of receptor is the beta-adrenergic receptor?

G-protein coupled receptor (GPCR).

What happens when epinephrine binds a GPCR?

Receptor changes shape and activates a G protein.

What are the three subunits of a G protein?

Alpha (α), beta (β), gamma (γ).

What activates the G protein?

Exchange of GDP → GTP.

What is the effector enzyme in this GPCR pathway?

Adenylate cyclase

What does adenylate cyclase produce?

cAMP from ATP.

What is cAMP?

A second messenger.

What enzyme does cAMP activate?

Protein kinase A (PKA).

What does PKA do?

Phosphorylates enzymes in a cascade.

What is the final result of this GPCR pathway?

Glycogen breakdown → glucose production.

What is signal amplification?

One signal produces many downstream effects.

What type of receptor is the insulin receptor?

Receptor tyrosine kinase (RTK).

What happens when insulin binds its receptor?

Autophosphorylation and activation of signalling cascade.

What second messenger is involved in insulin signaling?

PIP3

What is the final response of insulin signaling?

GLUT4 moves to membrane → increased glucose uptake

What is energy metabolism?

Pathways involved in generating or storing energy

What are the three macronutrients?

Carbohydrates, lipids, proteins

What is the main energy currency of the cell?

ATP

What happens when ATP is broken down?

ATP → ADP + Pi + energy.

How are lipids stored?

Triglycerides

How are carbohydrates stored?

Glycogen

Are proteins stored for energy?

No (only used in starvation)

What fuel does the brain prefer?

Glucose (brain)

What fuel does muscle use at rest?

Lipids (rest)

What fuel does muscle use during high intensity exercise?

Glucose (exercise)

What is catabolism?

Breakdown of molecules to release energy.

What is anabolism?

Synthesis of complex molecules.

What type of reactions occur in catabolism?

Oxidation.

What type of reactions occur in anabolism?

Reduction.

What is a metabolic pathway?

A series of enzyme-catalyzed reactions.

What are metabolic intermediates?

Molecules formed between steps in a pathway.