Unit 4 · Cell Communication and Cell Cycle

Cell-to-cell contact ● (core concept) — Cells communicate with one another through direct contact with other cells.

Chemical signaling ● (core concept) — Cells communicate from a distance via chemical signaling; signals released by one cell type travel long distances to target cells of another type.

Local regulators ● (core concept) — Signal molecules that act over short distances, targeting cells in the vicinity of the signal-emitting cell.

Immune cell interaction ○ — Immune cells interact through cell-to-cell contact, antigen-presenting cells (APCs), helper T-cells, and killer T-cells. Listed as an illustrative (suggested, not required) example in the CED.

Long-distance hormones ○ — Illustrative long-distance chemical messengers in the CED: insulin, human growth hormone, thyroid hormones, testosterone, and estrogen. Listed as illustrative (suggested, not required) examples.

Local signaling examples ○ — Illustrative short-distance messengers in the CED: neurotransmitters, plant immune responses, quorum sensing in bacteria, and morphogens in embryonic development. Listed as illustrative (suggested, not required) examples.

Signal transduction pathway ● (core concept) — A pathway that links signal reception with a cellular response. Many signal transduction pathways include protein modifications and involve phosphorylation cascades.

Ligand ● (core concept) — A chemical messenger — a peptide (protein) or small molecule — recognized by a receptor protein in a target cell.

Receptor protein ● (core concept) — A protein whose ligand-binding domain recognizes a specific chemical messenger. Receptors may be located on the surface of a target cell or in the cytoplasm or nucleus.

G protein-coupled receptor ● (core concept) — An example of a receptor protein in eukaryotes; after the ligand binds, the intracellular domain changes shape, initiating transduction of the signal.

Signaling cascade ● (core concept) — A sequence of steps that relays signals from receptors to cell targets, often amplifying the incoming signal and producing responses such as cell growth, secretion of molecules, or gene expression.

Second messenger ● (core concept) — Intracellular molecules, such as cyclic AMP (cAMP), that relay and amplify the signal inside the cell. Enzymes and second messengers work together in transduction.

Phosphorylation cascade ● (core concept) — A series of protein modifications (adding phosphate groups) that is common in signal transduction pathways and amplifies the signal.

Ligand-gated channel ● (core concept) — A membrane channel whose opening or closing is triggered by the binding of a ligand.

Hormone ● (core concept) — A signaling messenger that can travel long distances in the bloodstream to reach target cells.

Cellular response to signaling ● (core concept) — Signal transduction may result in changes in gene expression and cell function, which may alter phenotype or result in programmed cell death (apoptosis).

Apoptosis ● (core concept) — Programmed cell death, which may result from signal transduction pathways or from disruptions to the cell cycle. Explicitly named in EK 4.3.A.1 and 4.6.B.1.

Signaling pathway disruption ● (core concept) — Mutations in any domain of a receptor protein or any component of a signaling pathway may affect downstream components by altering signal transduction. Chemicals that interact with any component may activate or inhibit the pathway.

Quorum sensing ○ — Microbes use chemical messengers to communicate with nearby cells and regulate specific pathways in response to population density. Listed as an illustrative (suggested, not required) example in the CED.

Epinephrine and glycogen breakdown ○ — Epinephrine stimulates glycogen breakdown in mammals — an illustrative (suggested, not required) example of a signal transduction response in the CED.

Negative feedback ● (core concept) — A feedback mechanism that maintains homeostasis by reducing the initial stimulus. If a system is perturbed, negative feedback returns it to its target set point. Operates at molecular, cellular, and organismal levels.

Positive feedback ● (core concept) — A feedback mechanism that amplifies responses and processes: the variable initiating the response moves further from the initial set point as the stimulus intensifies, initiating additional responses that produce system change.

Homeostasis ● (core concept) — The maintenance of stable internal environments in response to internal and external changes, achieved through feedback mechanisms.

Blood sugar regulation ○ — Blood sugar regulation by insulin and glucagon — an illustrative (suggested, not required) example of feedback maintaining homeostasis in the CED.

Cell cycle ● (core concept) — A highly regulated series of events that controls the growth and reproduction of eukaryotic cells.

Interphase ● (core concept) — The portion of the cell cycle alternating with mitosis, consisting of the sequential stages G1, S, and G2.

G1 phase ● (core concept) — The first gap phase of interphase: the cell is metabolically active, duplicating organelles and cytosolic components.

S phase ● (core concept) — The synthesis phase of interphase: DNA in the form of chromatin replicates to form two sister chromatids connected at a centromere.

G2 phase ● (core concept) — The second gap phase of interphase: protein synthesis occurs, ATP is produced in large quantities, and centrosomes replicate.

G0 phase ● (core concept) — A stage in which a cell no longer divides but can reenter the cell cycle in response to appropriate cues. Nondividing cells may exit the cell cycle or be held at a particular stage.

Mitosis ● (core concept) — The process that ensures transfer of a complete genome from a parent cell to two genetically identical daughter cells in eukaryotes. It plays a role in growth, tissue repair, and asexual reproduction, occurring in sequential steps (prophase, metaphase, anaphase, telophase) alternating with interphase.

Prophase ● (core concept) — The first stage of mitosis: sister chromatids condense, the mitotic spindle begins to form, and centrosomes move to opposite poles of the cell.

Metaphase ● (core concept) — The stage of mitosis in which spindle fibers align chromosomes along the equator of the cell.

Anaphase ● (core concept) — The stage of mitosis in which paired sister chromatids separate as spindle fibers pull the chromatids toward opposite poles.

Telophase ● (core concept) — The final stage of mitosis: the mitotic spindle breaks down, a new nuclear envelope develops, and then the cytoplasm divides.

Cytokinesis ● (core concept) — Division of the cytoplasm: a cleavage furrow forms in animal cells or a cell plate forms in plant cells, resulting in two new daughter cells.

Sister chromatid ● (core concept) — One of two identical copies of a replicated chromosome, joined to its partner at the centromere.

Centromere ● (core concept) — The region of a chromosome where two sister chromatids are connected.

Mitotic spindle ● (core concept) — The structure of spindle fibers that forms in prophase and separates sister chromatids during mitosis.

Centrosome ● (core concept) — An organelle that replicates during G2 and moves to opposite poles of the cell to organize the mitotic spindle.

Cell cycle checkpoint ● (core concept) — Internal controls that regulate progression through the cell cycle.

Cyclin ● (core concept) — Proteins whose interactions with cyclin-dependent kinases control the cell cycle. (Knowledge of specific cyclin-CdK pairs or growth factors is beyond AP scope.)

Cyclin-dependent kinase ● (core concept) — Enzymes that, together with cyclins, control the cell cycle. (Knowledge of specific cyclin-CdK pairs is beyond AP scope.)

Cancer ● (core concept) — Uncontrolled cell division that can result from disruptions to the cell cycle (which may otherwise result in apoptosis).