Ap biology - Unit 4 Cell Communication

Cells communicate using chemical signals to coordinate actions like growth, reproduction, or defense.

What are the 3 steps of signal transduction?

Reception → Transduction → Response

What is a ligand?

A signal molecule that binds to a receptor.

What’s the difference between membrane-bound and intracellular receptors?

Membrane-bound = large/polar ligands; Intracellular = small/nonpolar ligands (e.g., steroids).

What is a second messenger? Give an example.

A small molecule that amplifies a signal inside the cell; e.g., cAMP, Ca²⁺.

What happens in the transduction step?

Signal is relayed and amplified, often by phosphorylation cascades.

What does negative feedback do?

Maintains homeostasis by reducing the effect of a stimulus.

What does positive feedback do?

Amplifies a response away from the set point.

Give two examples of negative feedback.

Blood sugar regulation (insulin), body temperature regulation.

Give two examples of positive feedback.

Labor contractions (oxytocin), fruit ripening.

What are the stages of the cell cycle (in order)?

G1 → S → G2 → Mitosis → Cytokinesis

What is G0 phase?

A resting/non-dividing phase.

What happens during the S phase?

DNA is replicated.

What does M phase include?

Mitosis (PMAT) + Cytokinesis

What proteins regulate the cell cycle?

Cyclins and Cyclin-dependent kinases (CdKs)

What can happen if signal pathways are disrupted?

Diseases like cancer or metabolic disorders can occur.

How does the cholera toxin affect cell signaling?

It causes overproduction of cAMP, leading to excessive ion/water loss.

What is apoptosis and when is it useful?

Programmed cell death; shapes body structures like fingers.