unit 4 bio vocab

Ligand

A signaling molecule that binds to a receptor to initiate a cellular response.

Receptor

A protein that detects a specific ligand and initiates signal transduction.

Signal Transduction Pathway

A series of molecular events that relay and amplify a signal to elicit a response.

Juxtacrine Signaling

Direct communication between adjacent cells via membrane-bound molecules or cell junctions.

Paracrine Signaling

Local signaling where cells release molecules that affect nearby target cells.

Autocrine Signaling

A cell produces a signal that it also responds to.

Endocrine Signaling

Long-distance signaling where hormones travel through the bloodstream to reach target cells.

G-Protein Coupled Receptor (GPCR)

A membrane receptor that activates a G-protein, triggering a signal cascade.

Receptor Tyrosine Kinase (RTK)

A membrane receptor that phosphorylates proteins to relay signals.

Ion Channel Receptor

A receptor that opens or closes an ion channel in response to ligand binding.

Second Messenger

Small molecules (e.g., cAMP, Ca²⁺) that amplify signals inside the cell.

Phosphorylation Cascade

A series of protein activations through phosphorylation, amplifying the signal.

cAMP (Cyclic AMP)

A common second messenger that activates protein kinases.

Protein Kinase

An enzyme that transfers phosphate groups to proteins, activating them.

Protein Phosphatase

An enzyme that removes phosphate groups from proteins, deactivating them.

Mutation

A change in DNA that may affect signal transduction (e.g., cancer-causing mutations).

Inhibitor

A molecule that blocks receptor function or signal transduction (e.g., drugs, toxins).

Apoptosis

Programmed cell death, often triggered by signal transduction pathways.

Homeostasis

The maintenance of stable internal conditions through feedback mechanisms.

Negative Feedback

A process that counteracts change to maintain balance (e.g., insulin regulation of blood sugar).

Positive Feedback

A process that amplifies change until a specific outcome is reached (e.g., childbirth contractions).

Cell Cycle

The sequence of events in a cell’s life, including growth and division.

Interphase

The longest phase of the cell cycle, where the cell grows and prepares for division.

G1 Phase

The first growth phase; the cell increases in size and prepares for DNA replication.

S Phase

DNA replication occurs, doubling the genetic material.

G2 Phase

The second growth phase; the cell prepares for mitosis.

Mitosis

The division of a cell’s nucleus into two identical nuclei.

Cytokinesis

The division of the cytoplasm to form two daughter cells.

Cell Cycle Checkpoints

Control points that regulate the cycle and prevent errors.

G1 Checkpoint

The main checkpoint; determines if a cell will divide or enter G0.

G2 Checkpoint

Ensures DNA replication was completed correctly before mitosis.

M Checkpoint

Ensures chromosomes are correctly attached to spindle fibers before separation.

Cyclin

A regulatory protein whose levels fluctuate to control the cell cycle.

Cyclin-Dependent Kinase (CDK)

An enzyme that, when bound to cyclin, regulates cell cycle progression.

Maturation Promoting Factor (MPF)

A complex of cyclin and CDK that promotes mitosis.

Growth Factor

A signaling molecule that stimulates cell division.

Density-Dependent Inhibition

A phenomenon where crowded cells stop dividing.

Anchorage Dependence

The requirement that cells must be attached to a surface to divide.

Cancer

Uncontrolled cell growth due to mutations in regulatory genes.

Tumor-Suppressor Gene

A gene that inhibits cell division; mutations can lead to cancer (e.g., p53).

p53 Gene

A tumor suppressor that halts the cell cycle if DNA damage is detected.

Proto-Oncogene

A normal gene that promotes cell division; when mutated, it becomes an oncogene, leading to uncontrolled growth.

Oncogene

A mutated gene that drives uncontrolled cell division, leading to cancer.

Metastasis

The spread of cancer cells to other parts of the body.

Benign Tumor

A non-cancerous mass of cells that do not spread.

Malignant Tumor

A cancerous mass that invades surrounding tissues.