AP Biology Unit 4: Cell Communication and Cell Cycle Review

Vocabulary practice flashcards covering key definitions, signaling mechanisms, feedback pathways, cell cycle stages, and regulatory checkpoints from the AP Biology Unit 4 lecture.

Autocrine Signaling

A form of short-distance cell signaling where a cell secretes a signaling molecule that binds to receptors on the very same cell.

Paracrine Signaling

A type of local cell signaling where signaling molecules are released into the extracellular fluid to target and bind to nearby cells.

Endocrine Signaling

Long-distance signaling in which signaling molecules, such as hormones, are secreted into the bloodstream to travel throughout the body to target cells.

Ligand

A chemical signaling molecule that specifically binds to an active site on a complementary receptor protein, causing a conformational shape change.

Steroid Hormone

A non-polar lipid signaling molecule that diffuses directly across the plasma membrane to bind to an intracellular receptor located in the cytosol or nucleus.

Protein Hormone

A polar signaling molecule released from cells via exocytosis that cannot pass through the non-polar plasma membrane and must bind to an extracellular cell-surface receptor.

Signal Transduction Pathway

A three-step cellular process consisting of reception (ligand binding to receptor), transduction (intracellular relay and amplification cascades), and cellular response.

Protein Kinase

An enzyme that transfers phosphate groups to relay molecules, typically proteins, during a phosphorylation cascade to activate them.

Secondary Messenger

Small, non-protein intracellular signaling molecules, such as cyclic AMP ($\text{cAMP}$) or calcium ions ($\text{Ca}^{2+}$), that relay and amplify signals inside the cytosol.

Adenylyl Cyclase

An enzyme activated during G-protein signaling pathways that catalyzes the conversion of $\text{ATP}$ into cyclic AMP ($\text{cAMP}$).

Apoptosis

Programmed cell death in which a cell systematically digests itself from the inside out in response to specific developmental cues or irreparable cellular damage.

Negative Feedback

A regulatory feedback mechanism that counteracts a disruption by reducing the initial stimulus to maintain homeostasis and return the system to its set point.

Positive Feedback

A regulatory feedback mechanism that amplifies and builds upon an initial stimulus, driving the physiological process further away from the baseline set point to achieve an outcome.

G1 Phase

The first growth phase of interphase in which the cell is metabolically active, duplicating its organelles and cytosolic components.

S Phase

The synthesis phase of interphase during which DNA replication occurs to produce two identical copies of each chromosome.

G2 Phase

The second gap phase of interphase where the cell synthesizes necessary proteins, produces large quantities of $\text{ATP}$, and replicates its centrosomes in preparation for cell division.

G0 Phase

A non-dividing, quiescent resting state entered by cells that do not receive the signals required to pass the G1 checkpoint.

Centrosome

The microtubule-organizing center of the cell that replicates during G2 and migrates to opposite cell poles during prophase to organize the mitotic spindle.

Sister Chromatids

Two identical copies of a replicated chromosome joined together at a shared region called the centromere.

Kinetochore

A protein structure located at the centromere of sister chromatids where spindle microtubules attach during metaphase.

Separase

An enzyme that cleaves the cohesive protein linkages holding sister chromatids together, enabling their separation to opposite poles during anaphase.

Cleavage Furrow

A shallow groove formed by a contracting ring of actin microfilaments that pinches an animal cell into two separate daughter cells during cytokinesis.

Cell Plate

A structure formed in plant cells during cytokinesis by the coalescing of vesicles delivering primary cell wall components, dividing the cytoplasm in two.

G1 Checkpoint

A cell cycle control point that evaluates cell size, nutrient reserves, growth factor signaling (such as PDGF), and DNA integrity before committing the cell to division.

G2 Checkpoint

A regulatory checkpoint occurring after S phase that halts cycle progression if DNA replication is incomplete or if damaged DNA is detected.

M Checkpoint

A spindle assembly checkpoint occurring during metaphase that ensures every sister chromatid is correctly attached to spindle microtubules prior to anaphase separation.

Cyclin-Dependent Kinase (CDK)

A kinase enzyme present at constant levels throughout the cell cycle that becomes enzymatically active only when bound to its specific regulatory protein, cyclin.

p53

A tumor suppressor gene that detects DNA damage and activates CDK inhibitors to arrest the cell cycle for repair or trigger apoptosis if the damage is irreparable.