Cell Signaling Pathways: Types, Receptors, and Responses in Biology

What are the three main steps of signal transduction?

Reception → Transduction → Response.

What happens during reception?

A signaling molecule (ligand) binds to a receptor protein on the cell's surface or inside the cell.

What happens during transduction?

The signal is relayed through relay molecules, often using phosphorylation cascades.

What happens during response?

The cell initiates a specific activity such as gene expression, growth, or apoptosis.

What are the three main types of cell signaling?

Direct contact, local signaling, and long-distance signaling.

What are ligand-gated ion channels?

Receptors that open ion channels when a ligand binds.

What are G-protein-coupled receptors (GPCRs)?

Receptors that activate G proteins when bound by a signal molecule, triggering a cascade of events.

What are intracellular receptors?

Receptors located inside the cell that bind lipid-soluble molecules such as steroid hormones.

What kinds of molecules bind to intracellular receptors?

Nonpolar, lipid-soluble molecules (e.g., steroid hormones).

What is p53's function in the DNA damage pathway?

p53 leads to inhibition of the cell cycle when DNA is damaged.

What is MDM2's function in the pathway?

MDM2 inhibits p53, allowing the cell cycle to continue.

How does DNA damage affect this pathway?

DNA damage inhibits MDM2, allowing p53 to become active and stop the cell cycle.

What are second messengers?

Small, non-protein molecules that relay signals inside the cell (e.g., cAMP, Ca²⁺).

What is phosphorylation?

The addition of a phosphate group (by kinases) to activate or deactivate proteins.

What enzyme removes phosphate groups?

Phosphatase.

What is a phosphorylation cascade?

A series of reactions in which one enzyme activates another, amplifying the signal.

What are examples of cellular responses to signals?

Activation of gene expression, protein synthesis, cell growth/division, secretion of molecules, or apoptosis.

What causes apoptosis?

Signaling pathways that activate programmed cell death in response to damage or stress.

How can mutations affect signal transduction?

They can alter receptor shape or affinity, preventing proper binding or response.

What can happen if p53 is mutated?

Cells may continue dividing with damaged DNA, increasing cancer risk.

What is a ligand?

A signaling molecule that binds to a receptor.

What is a receptor protein?

A protein that detects a signaling molecule and initiates a response.

What is a relay molecule?

A molecule that passes the signal along during transduction.

What is transcription in this context?

The process of creating mRNA from DNA, often triggered by signal transduction pathways.