Chapter 11: Cell Division and DNA Replication

Comprehensive vocabulary flashcards covering Chapter 11 on binary fission, eukaryotic cell cycle phases, DNA replication mechanisms and enzymes, mitosis stages, cytokinesis, cell cycle checkpoints, cyclin-CDK regulation, apoptosis, and cancer biology.

Binary Fission

The process of cell division in prokaryotes where the circular bacterial DNA molecule attaches to the inner cell membrane, replicates bidirectionally, and separates into two daughter cells as the cell elongates and synthesizes a new cell membrane and cell wall.

M Phase

The phase of the eukaryotic cell cycle during which the parent cell divides into two daughter cells, consisting of mitosis and cytokinesis.

Interphase

The phase of the eukaryotic cell cycle occurring between two successive M phases, comprising the $G_1$, S, and $G_2$ phases.

$G_1$ Phase

The stage of interphase characterized by cell growth, expression of regulatory proteins, and preparation for DNA synthesis.

S Phase

The stage of interphase during which DNA synthesis (replication) occurs.

$G_2$ Phase

The stage of interphase in which the cell prepares for mitosis and cytokinesis.

$G_0$ Phase

A cell cycle arrest state occurring in cells that are not actively dividing, where no preparation for cell division takes place.

Semiconservative Replication

The mechanism of DNA replication—demonstrated by Meselson and Stahl ($1958$) using isotopes $^{15}\text{N}$ and $^{14}\text{N}$—in which each replicated DNA duplex consists of one intact parental strand and one newly synthesized daughter strand.

Conservative Replication

A hypothesized model of DNA replication proposing that the original parental DNA duplex remains intact and an entirely new duplex composed of two daughter strands is synthesized.

DNA Helicase

An enzyme that unwinds and separates the two strands of the parental DNA double helix at the replication fork.

Topoisomerase II

An enzyme that relieves the torsional stress caused by the unwinding of the DNA double helix upstream of the replication fork.

Single-Strand Binding Protein (SSBP)

A protein that binds to and stabilizes single-stranded parental DNA during replication to prevent the strands from reannealing.

RNA Primase

An RNA polymerase enzyme that synthesizes a short RNA primer complementary to the DNA template to provide a free $3'\text{-OH}$ group for DNA polymerase.

DNA Polymerase

An enzyme complex that elongates a growing DNA strand in the $5'$ to $3'$ direction by catalyzing the attack of the $3'\text{-OH}$ group on the high-energy phosphate bond of an incoming deoxynucleotide.

Leading Strand

The daughter DNA strand synthesized continuously in the $5'$ to $3'$ direction toward the advancing replication fork.

Lagging Strand

The daughter DNA strand synthesized discontinuously in the direction away from the replication fork as a series of short segments.

Okazaki Fragments

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

DNA Ligase

An enzyme that seals gaps in the sugar-phosphate backbone by joining adjacent Okazaki fragments after RNA primers have been replaced with DNA.

DNA Proofreading

An enzymatic repair function of DNA polymerases in which incorrect, non-complementary nucleotides are recognized, excised, and replaced with the correct base.

Telomeres

Non-coding repetitive DNA sequences ($5'\text{-TTAGGG-3'}$ repeated $1500$ to $3000$ times in humans) capping the ends of eukaryotic chromosomes to prevent the loss of genetic coding information during successive rounds of replication.

Telomerase

A ribonucleoprotein enzyme containing an internal RNA template that elongates the shortened $3'$ ends of eukaryotic chromosomes in germ cells and stem cells.

Homologous Chromosomes

Pairs of matching chromosomes carrying the same genes at the same loci, with one member of each pair inherited from each parent.

Sister Chromatids

Two identical copies of a replicated chromosome produced during S phase that remain physically connected at the centromere until anaphase.

Centromere

A specialized region of a chromosome where sister chromatids are held together and where kinetochores assemble.

Kinetochore

A protein structure located on the centromere of each sister chromatid that serves as the attachment site for spindle microtubules originating from opposite poles.

Prophase

The first stage of mitosis, during which chromosomes condense, centrosomes begin radiating microtubules, and the two centrosomes migrate toward opposite poles.

Prometaphase

The stage of mitosis marked by the breakdown of the nuclear envelope and the attachment of spindle microtubules to the kinetochores of chromosomes.

Metaphase

The stage of mitosis during which chromosomes align along a single plane in the center of the dividing cell.

Anaphase

The stage of mitosis where centromeres divide and sister chromatids separate into individual chromosomes that travel toward opposite spindle poles.

Telophase

The final stage of mitosis during which chromosomes arrive at opposite poles, decondense, the mitotic spindle breaks down, and nuclear envelopes re-form around each set of chromosomes.

Contractile Ring

A ring of actin microfilaments that forms beneath the plasma membrane during animal cell cytokinesis, pinching the cell inward to divide the cytoplasm.

Cell Plate

A structure formed in the center of a dividing plant cell during cytokinesis that expands outward to fuse with the parental cell wall, establishing two distinct daughter cells.

Cyclins

A family of regulatory proteins whose levels rise and fall periodically throughout the cell cycle, functioning to bind and activate cyclin-dependent kinases (CDKs).

Cyclin-Dependent Kinases (CDKs)

Enzymes that, when activated by cyclins, phosphorylate specific target proteins to drive the cell through successive stages of the cell cycle.

Cyclin D-CDK and Cyclin E-CDK Complexes

Cyclin-kinase complexes active during the $G_1$ phase that phosphorylate target proteins to prepare the cell for DNA synthesis.

Cyclin A-CDK Complex

A cyclin-kinase complex active during S phase that initiates DNA synthesis and prevents the genome from replicating more than once per cycle.

Cyclin B-CDK Complex

A cyclin-kinase complex active during $G_2$ phase that prepares the eukaryotic cell for entry into mitosis.

DNA Damage Checkpoint

A cell cycle checkpoint that operates before entry into S phase to verify DNA integrity, arresting cycle progression if DNA damage is detected.

DNA Replication Checkpoint

A checkpoint operating at the end of $G_2$ phase that blocks entry into mitosis until all DNA has been completely and accurately replicated.

Spindle Assembly Checkpoint

A checkpoint operating during M phase before anaphase that delays chromosome separation until all kinetochores are properly attached to spindle microtubules.

p53 Protein

A nuclear tumor suppressor protein that is phosphorylated by protein kinases in response to DNA damage, activating transcription of genes that inhibit the cell cycle to allow time for DNA repair.

Apoptosis

Programmed cell death, a process triggered by signals such as excess Bax forming Bax/Bax homodimers rather than harmless Bax/Bcl-2 heterodimers.

Proto-oncogenes

Normal cellular genes encoding proteins that promote cell division, which have the potential to become cancer-causing oncogenes if mutated.

Oncogene

A mutated, cancer-causing form of a proto-oncogene that drives uncontrolled cellular proliferation.

Tumor Suppressors

Genes encoding proteins whose normal activities restrain the cell cycle, promote DNA repair, or induce apoptosis to prevent tumor formation.