Cell Bio Cell Signaling Principles

What is signal transduction?

Converting an extracellular signal into an intracellular signaling molecule/response (like radio signal in → sound out).

Name the four ranges of signaling.

Endocrine, paracrine, neuronal, contact-dependent (mnemonic SSD: speed, selectivity, distance). Autocrine = a cell responds to a mediator it made itself.

Which signaling type uses the bloodstream, and which releases no signal at all?

Endocrine uses the blood and acts far away; contact-dependent releases nothing (a membrane-bound signal binds a neighbor's receptor).

Cortisol, estradiol, and testosterone are derivatives of what?

Cholesterol (steroids). Epinephrine and thyroxine are tyrosine derivatives; insulin is a protein from pancreatic β cells.

Why does cortisol use an intracellular receptor while EGF uses a cell-surface receptor?

Cortisol is small and hydrophobic so it crosses the plasma membrane; EGF is a large protein that cannot.

Why is acetylcholine-triggered muscle contraction fast but EGFR-driven growth slow?

Contraction alters existing proteins (seconds to minutes); growth needs changes in gene expression and new protein synthesis (minutes to hours).

Acetylcholine slows heart cells, triggers secretion in salivary cells, and contracts muscle. What explains the different responses?

Each cell type has its own receptors and its own intracellular relay and effector proteins.

RAIDM: the five jobs of intracellular signaling proteins

Relay, Amplify, Integrate, Distribute, Modulate via feedback.

What do second messengers do? Give examples.

They amplify: one activated enzyme makes many small molecules that usually activate a kinase. Examples: cAMP, IP₃, DAG, Ca²⁺.

What are the two main types of molecular switches?

Phosphorylation (kinase adds phosphate from ATP = ON; phosphatase removes it = OFF) and GTP-binding (GTP = ON, GDP = OFF; GTP hydrolysis turns it off).

How do GEFs and GAPs change a monomeric GTPase such as Ras?

GEF swaps GDP for GTP (ON); GAP stimulates GTP hydrolysis (OFF).

What can positive and negative feedback do?

Positive feedback can ignite an explosive response (e.g., triggering cell division); negative feedback can generate oscillations.

What are the six steps of signal transduction?

Synthesis of ligand → release → transport → detection by the target cell's receptor → response through a signaling cascade → removal of the signal (turn-off).