The Cell Cycle, Regulation, and the Molecular Genetics of Cancer

Vocabulary practice flashcards covering cell cycle phases, mitosis stages, molecular regulatory mechanisms (cyclins, Cdks, checkpoints), and the genetics of cancer (oncogenes and tumor suppressors).

Genome

A cell's complete set of DNA.

Chromatin

A complex of DNA and structural proteins, such as histones forming nucleosomes, that constitutes eukaryotic chromosomes.

Euchromatin

The uncondensed, active chromatin state that is accessible for transcription.

Heterochromatin

The highly condensed, transcriptionally silent chromatin state.

Somatic Cells

All nonreproductive body cells containing two complete sets of chromosomes ($2n$) as paired homologous chromosomes.

Gametes

Reproductive cells (sperm and egg cells) containing half the chromosome number of somatic cells ($n$).

Sister Chromatids

Two identical copies of an original duplicated chromosome joined tightly along their lengths by protein complexes called cohesins.

Centromere

The narrow waist region of a duplicated chromosome where two sister chromatids are most closely bound.

Kinetochore

A specialized protein complex located at the centromere region of each sister chromatid that serves as the attachment point for spindle microtubules.

Mitosis

The division of the genetic material contained within the cell nucleus into two identical sets.

Cytokinesis

The subsequent division of the cytoplasm following mitosis, yielding two distinct daughter cells.

Meiosis

A specialized variation of cell division producing nonidentical daughter cells that contain only one set of chromosomes ($n$).

$G_1$ Phase

The first gap phase of interphase characterized by major cellular growth, intense metabolic activity, organelle production, and nutrient accumulation.

S Phase

The synthesis phase of interphase during which cellular growth continues and genome duplication occurs exclusively through DNA replication.

$G_2$ Phase

The second gap phase of interphase involving final growth and preparation for division, synthesis of tubulin, replication of centrioles in animal cells, and tighter coiling of chromatin.

Prophase

The first mitotic stage in which chromatin fibers condense into visible chromosome pairs, nucleoli disappear, the mitotic spindle begins forming, and centriole pairs migrate toward opposite poles.

Prometaphase

The mitotic stage where the nuclear envelope completely disassembles, spindle microtubules invade the nuclear region, and kinetochore microtubules attach to sister chromatid kinetochores.

Metaphase

The mitotic stage where all chromosomes align along the metaphase plate equidistant between the spindle poles under mechanical tension.

Anaphase

The mitotic stage triggered by separase cleaving centromeric cohesins, causing sister chromatids to split instantly into daughter chromosomes and move toward opposite poles.

Anaphase A

The mechanism of chromosome movement in which kinetochore microtubules shorten as kinetochore motor proteins pull daughter chromosomes toward opposite spindle poles.

Anaphase B

The mechanism of chromosome movement in which nonkinetochore polar microtubules slide past one another and elongate, pushing spindle poles apart and lengthening the cell.

Telophase

The final stage of mitosis during which two daughter nuclei form, nuclear envelopes and nucleoli reassemble, chromosomes decondense into diffuse chromatin, and the mitotic spindle disassembles.

Centrosome

The primary microtubule-organizing center (MTOC) in animal cells that contains a pair of centrioles and directs spindle formation.

Asters

Radial, star-like arrays of short microtubules that extend from centrosomes toward the plasma membrane in animal cells.

Separase

The enzyme that cleaves centromeric cohesin proteins during anaphase to allow sister chromatids to separate.

Shugoshin ($Sgo1$)

A protective protein that shields centromeric cohesins from premature cleavage prior to anaphase.

Cleavage Furrow

The cytokinesis structure in animal cells produced by a contractile ring of actin microfilaments and myosin motor proteins that pinches inward centripetally.

Cell Plate

The cytokinesis structure in plant cells formed along the metaphase plate by the centrifugal fusion of Golgi-derived vesicles to synthesize a new cell wall.

Binary Fission

The asexual reproductive process in prokaryotes where the circular chromosome replicates starting at the origin of replication, followed by cell elongation and septation.

Cell Cycle Control System

A cyclically operating internal regulatory network in the cytoplasm that directs cell cycle progression and stops at specific checkpoints until go-ahead signals are received.

$G_1$ Checkpoint

The restriction point in late $G_1$ that assesses environmental conditions, cell size, nutrient availability, growth factors, and DNA damage to decide whether to enter S phase or exit into $G_0$.

$G_0$ Phase

A nondividing, resting state entered by a cell that does not receive a go-ahead signal at the $G_1$ checkpoint.

$G_2$ Checkpoint

The regulatory transition point checking for complete and accurate DNA replication, cell size, and sufficient ATP levels prior to activating MPF and entering mitosis.

M Checkpoint

The spindle checkpoint at the metaphase-to-anaphase transition that assesses whether all sister chromatid kinetochores are properly attached to spindle microtubules under tension.

Cyclin-Dependent Kinases (Cdks)

Protein kinases maintained at relatively constant concentrations that require binding to fluctuating cyclin proteins to phosphorylate target substrates.

Cyclins

Regulatory proteins whose cellular concentrations fluctuate cyclically, accumulating through late S and $G_2$ to bind and activate Cdks.

Maturation-Promoting Factor (MPF)

A cyclin-Cdk complex that activates in late $G_2$, peaks in activity during metaphase, and triggers entry into M phase by phosphorylating structural proteins.

Platelet-Derived Growth Factor (PDGF)

An external protein factor released by platelets that binds surface receptors on fibroblasts to trigger passage through the $G_1$ checkpoint and promote proliferation.

Transformation

The process by which a normal cell acquires the capacity to divide indefinitely, evading immune destruction and cell cycle controls.

Benign Tumor

A localized mass of abnormal cells that remains at its original site because it lacks the genetic capacity to invade surrounding tissue.

Malignant Tumor

An invasive mass of transformed cells capable of impairing the functions of one or more organs.

Metastasis

The process by which malignant cells detach from a primary tumor, travel through blood or lymph vessels, and establish secondary tumors in distant tissues.

Proto-oncogenes

Normal cellular genes that encode proteins responsible for stimulating normal cell growth and division.

Oncogenes

Mutated, hyperactive versions of proto-oncogenes that cause an abnormal increase in the amount or activity of growth-stimulating proteins.

Tumor-Suppressor Genes

Genes that encode proteins that normally inhibit cell division, repair damaged DNA, control cellular adhesion, or trigger apoptosis.

Ras Protein

A G protein encoded by the ras proto-oncogene that relays growth factor signals to a cytoplasmic kinase cascade to stimulate cell division.

$p53$ Gene

A tumor-suppressor gene known as the guardian of the genome that arrests the cell cycle at $G_1$, activates DNA repair genes, or triggers apoptosis via Bax when damage is irreparable.

$BRCA1$ and $BRCA2$

Caretaker tumor-suppressor genes that function with $RAD51$ to conduct precision homologous recombination repair (HRR) on double-strand DNA breaks.