Chapter 11: The Cell Cycle, DNA Replication, and Mitotic Cell Division

Vocabulary flashcards covering key terms and definitions on prokaryotic binary fission, eukaryotic mitotic cell division, DNA replication mechanisms and enzymes, chromosome structures, and cell cycle checkpoints and regulation.

Binary Fission

The form of cell division in prokaryotes, such as bacteria and archaea, in which a cell replicates its DNA, increases in size, and divides into two genetically identical daughter cells.

FtsZ

A bacterial gene and encoded protein related to tubulin that forms a ring at the midpoint constriction to direct the synthesis of new membrane and cell wall during binary fission.

Mitotic Cell Division

The division of a eukaryotic somatic cell consisting of mitosis (nuclear division) followed by cytokinesis (cytoplasmic division) to generate two genetically identical daughter cells.

Interphase

The period between two successive $M$ phases in the eukaryotic cell cycle during which the cell grows, synthesizes proteins, and replicates its DNA; comprises $G_1$, $S$, and $G_2$ phases.

$S$ Phase

The synthesis phase of interphase during which the cell replicates its chromosomal DNA.

$G_1$ Phase

The gap phase between the completion of $M$ phase and the start of $S$ phase during which regulatory proteins such as kinases are made in preparation for DNA synthesis.

$G_2$ Phase

The gap phase between the end of $S$ phase and the onset of $M$ phase during which cell size and protein content increase in preparation for mitosis and cytokinesis.

$G_0$ Phase

A nondividing resting state paused between $M$ phase and $S$ phase where cells perform specialized physiological functions without preparing for DNA replication.

Semiconservative Replication

The mechanism of DNA replication in which each newly formed double-stranded DNA molecule consists of one parental template strand and one newly synthesized daughter strand.

Replication Fork

The Y-shaped site where parental strands of double-stranded DNA unwind and separate into single strands to serve as templates for synthesis.

Helicase

An enzyme that breaks hydrogen bonds holding base pairs together to unwind and separate the two parental strands at the replication fork.

Single-Strand Binding Protein

A protein that binds to exposed single-stranded template DNA regions to stabilize them and prevent them from snapping back together during replication.

Topoisomerase II

An enzyme that works upstream of the replication fork, cutting both DNA strands to relieve the torsional unwinding stress and rewinding them in the opposite direction.

RNA Primase

An enzyme that synthesizes a short complementary RNA starter sequence on the parental DNA template, providing a free $3'$ hydroxyl group for DNA polymerase.

DNA Polymerase

An enzyme that synthesizes a new DNA strand complementary to an existing template by adding incoming deoxynucleotides exclusively to the $3'$ hydroxyl end in the $5' \rightarrow 3'$ direction.

Leading Strand

The daughter DNA strand whose $3'$ end points toward the replication fork, allowing it to be synthesized as one continuous polymer as the double helix unwinds.

Lagging Strand

The daughter DNA strand whose $5'$ end points toward the replication fork, requiring synthesis away from the fork in short, discontinuous fragments.

Okazaki Fragments

The short, discontinuous segments of newly synthesized DNA formed on the lagging strand, each initiated with an RNA primer.

DNA Ligase

An enzyme that joins adjacent fragments of DNA together by catalyzing phosphodiester bond formation after RNA primers are removed and replaced with DNA.

Proofreading

An intrinsic enzymatic activity of DNA polymerase that detects mismatched nucleotide pairs, cleaves the incorrect base, and replaces it with the proper complementary base.

Origin of Replication

A specific sequence or location on a DNA molecule at which replication is initiated.

Replication Bubble

The opening formed by the unwinding of double-stranded DNA at an origin of replication, featuring two replication forks progressing in opposite directions.

Telomere

A repeating, non-gene-coding sequence (such as $5'\text{-TTAGGG-}3'$ in humans) capping the ends of eukaryotic linear chromosomes to buffer against sequence loss during replication.

Telomerase

An enzyme containing an RNA template that restores shortened chromosome tips by adding complementary repetitive DNA sequences to the $3'$ ends of linear chromosomes.

Karyotype

The standard portrait depicting the characteristic number, sizes, and shapes of condensed chromosomes representative of a given species.

Homologous Chromosomes

Pairs of chromosomes of the same type that carry the same set of genes, one inherited from each parent.

Sister Chromatids

Two identical copies of a chromosome produced during DNA replication in $S$ phase that remain joined together at the centromere.

Centromere

A constricted region on a replicated chromosome that physically holds sister chromatids together and serves as the assembly site for kinetochores.

Kinetochore

A specialized protein complex assembled on each side of the centromere that forms the attachment point for a mitotic spindle microtubule.

Centrosome

The microtubule-organizing center of animal cells that duplicates in $S$ phase and migrates to opposite poles during prophase to organize the mitotic spindle.

Prophase

The first stage of mitosis, marked by chromosome condensation, migration of centrosomes to opposite poles, and the radiation of spindle microtubules.

Prometaphase

The second stage of mitosis, characterized by the breakdown of the nuclear envelope and the attachment of spindle microtubules to chromosomal kinetochores.

Metaphase

The mitotic stage during which chromosomes align in a single plane across the middle of the dividing cell equidistant from both poles.

Anaphase

The mitotic stage where centromeres split, separating sister chromatids into individual chromosomes that are pulled by shortening microtubules to opposite poles.

Telophase

The final stage of mitosis during which nuclear envelopes re-form around decondensing chromosomes at each pole, creating two new distinct nuclei as the spindle dissolves.

Contractile Ring

A cytoskeletal ring of actin filaments and motor proteins that forms beneath the equatorial membrane of dividing animal cells, pinching the cytoplasm into two daughter cells.

Phragmoplast

A plant-specific structure composed of overlapping microtubules that guides vesicles containing cell wall components to the center of the dividing cell during cytokinesis.

Cell Plate

The developing new cell wall formed in the middle of a dividing plant cell by fusing vesicles, which expands until it joins the original peripheral wall.

Cyclin

A regulatory protein whose concentration rises and falls in an oscillating cycle to activate cyclin-dependent kinases at specific transitions of the cell cycle.

Cyclin-Dependent Kinase (CDK)

A kinase that remains present at steady levels throughout the cell cycle but becomes active only when bound to a specific cyclin, phosphorylating target proteins to drive cell division.

Checkpoint

A cellular control mechanism that monitors preparations or damage at key transitions and halts cell cycle progression if conditions are not met.

p53

A tumor suppressor protein termed the 'guardian of the genome' that is phosphorylated upon DNA damage, stimulating transcription of p21 to arrest the cell cycle or initiating apoptosis.

Apoptosis

A genetically programmed, controlled pathway of cellular self-destruction that eliminates unneeded, heavily damaged, or potentially cancerous cells.

Oncogene

A mutated, hyperactive version of a gene that promotes unregulated cell division, contributing to the development of cancer.

Proto-Oncogene

A normal cellular gene encoding a component of a division-promoting pathway (such as a growth factor, receptor, or kinase) that can cause cancer when mutated.

Tumor Suppressor

A protein whose activity inhibits cell division, activates cell cycle checkpoints, promotes DNA repair, or triggers apoptosis to prevent cancerous growth.

Multinucleate Cell

A single cell that contains two or more nuclei, resulting from the completion of nuclear division (mitosis) without cytoplasmic division (cytokinesis).