AP Biology Cell Communication and Cell Cycle

Ligand

A signaling molecule that binds specifically to a receptor.

Target Cell

A cell possessing the correct receptor for a signaling molecule.

Autocrine Signaling

Cellular communication where a cell signals itself.

Paracrine Signaling

Signaling process where molecules target nearby cells.

Endocrine Signaling

Long-distance communication using hormones traveling through the bloodstream.

Synaptic Signaling

Neurotransmitter-based communication across a tiny gap between neurons.

Juxtacrine Signaling

Contact-dependent communication requiring direct physical contact between cells.

G Protein-Coupled Receptor

Membrane receptor that activates an internal G protein upon ligand binding.

Receptor Tyrosine Kinase

Membrane receptor that dimerizes and autophosphorylates upon ligand binding.

Ligand-Gated Ion Channel

Membrane receptor that opens or closes to allow ion passage.

Intracellular Receptor

Cytoplasmic or nuclear receptor for lipid-soluble signaling molecules.

Signal Transduction

Conversion of an external extracellular signal into an internal cellular response.

Protein Kinase

Enzyme that transfers a phosphate group from ATP to proteins.

Protein Phosphatase

Enzyme that removes phosphate groups from proteins.

Phosphorylation Cascade

Sequential activation of protein kinases that amplifies an intracellular signal.

Second Messenger

Small internal molecule that relays and amplifies signals inside the cell.

cAMP

Second messenger produced from ATP by adenylyl cyclase.

Signal Amplification

Process where one initial signal triggers a massively multiplied cellular response.

Apoptosis

Controlled program of cell death that destroys damaged or unnecessary cells.

Caspase

Protease enzyme that acts as the demolition crew during apoptosis.

Negative Feedback

Regulatory loop that reduces the initial stimulus to maintain homeostasis.

Positive Feedback

Regulatory loop that amplifies the original stimulus until an endpoint.

Interphase

Cell cycle phase consisting of G1, S, and G2 stages.

S Phase

Stage of interphase where DNA replication occurs.

G0 Phase

Resting stage where cells exit the cell cycle and function normally.

Cyclin

Regulatory protein whose concentration fluctuates to control the cell cycle.

Cyclin-Dependent Kinase (CDK)

Enzyme activated by cyclins to trigger cell cycle events.

Mitosis

Nuclear division process resulting in two identical daughter cells.

Metaphase Plate

Imaginary equatorial plane where chromosomes align during metaphase.

Cleavage Furrow

Contractile ring of actin proteins that pinches animal cells apart.

Cell Plate

Vesicle-derived structure that forms a new cell wall in plants.

Diploid (2n)

Cell state containing two complete sets of chromosomes.

Haploid (n)

Cell state containing a single set of unpaired chromosomes.

Homologous Chromosomes

Chromosome pair of matching size, shape, and genes.

Sister Chromatids

Identical copies of a chromosome connected at the centromere.

Synapsis

Pairing of homologous chromosomes during Prophase I of meiosis.

Crossing Over

Exchange of genetic material between non-sister homologous chromatids.

Independent Assortment

Random alignment of homologous chromosome pairs during Metaphase I.

Nondisjunction

Failure of chromosomes or chromatids to separate properly during division.

Semiconservative Replication

DNA replication mode yielding molecules with one old and one new strand.