Biology 1003 - Unit 5: Cell Division, Regulation, Cancer, and Meiosis

Comprehensive vocabulary flashcards covering bacterial binary fission, eukaryotic mitosis, cell cycle regulation, checkpoints, cyclins/CDKs, cancer biology, and the mechanisms of meiosis and genetic variation from Biology 1003 Unit 5.

Asexual Reproduction

A form of reproduction where new offspring that are genetically identical to the parent are produced by a single parent organism.

DNA Replication

The process of duplicating chromosomes prior to cell division, occurring during the $S$ phase in eukaryotes and at the beginning of binary fission in prokaryotes.

Mitosis

The division of the eukaryotic cell nucleus that separates duplicated chromosomes into two identical nuclei for growth, tissue repair, and regeneration.

Cytokinesis

The division of the cytoplasm and cellular contents into two separate daughter cells, which may be of equal size (as in animal cell division) or unequal size (as in yeast budding and human oogenesis).

Binary Fission

The method of asexual reproduction utilized by prokaryotes comprising concurrent DNA replication, cell elongation, chromosome segregation, and cytokinesis.

FtsZ

A bacterial protein that migrates to the midpoint of an elongating cell, forms a ring at the periphery between replicated chromosomes, and directs membrane constriction and septum wall formation.

Septum

A dividing new cell wall and plasma membrane partition synthesized during binary fission that splits the bacterial cell into two compartments.

Origin of Replication (ori)

The specific sequence site on a bacterial circular chromosome or eukaryotic linear chromosome where DNA replication begins bi-directionally.

Plasmid

Small, extrachromosomal circular DNA found in variable copy numbers in some bacteria (and yeast) that replicates independently via its own ori and confers selective advantages like antibiotic resistance.

Somatic Cells

All non-reproductive diploid cells of the body tissues and organs that exclusively divide by mitosis.

Terminally Differentiated Cells (TDCs)

Specialized body cells permanently arrested in the $G_0$ state that perform specialized metabolic roles but never undergo cell division (e.g., neurons, cardiac myocytes, skeletal muscle cells, and osteocytes).

Germline Cells

Reproductive lineage cells found in the gonads (testes and ovaries) that transmit genetic information to offspring, including stem cells that perform mitosis and cells undergoing meiosis to produce gametes.

Spermatogonia

Diploid ($2n$) male germline stem cells located in the testes that continuously regenerate their population via mitosis throughout life while producing cells that undergo meiosis.

Oogonia

Diploid ($2n$) female germline stem cells in the ovaries whose mitotic regeneration permanently ceases before birth, establishing all the potential egg cells a female will ever possess.

Interphase

The period of the eukaryotic cell cycle comprising $G_1$, $S$, and $G_2$ phases, accounting for roughly $90\%$ of a cell's life span, dedicated to normal metabolic roles, growth, and chromosome duplication.

$G_0$ Phase

A quiescent, non-dividing resting state where a cell exits the active division cycle to carry out specialized metabolic functions; reversible for many cell types but permanent in terminally differentiated cells.

Autosomes

Non-sex chromosomes that appear in homologous pairs numbered $1$ through $22$ in humans.

Allosomes

Sex chromosomes ($X$ and $Y$ in humans) that determine biological sex and share only a small terminal region of homology for pairing during division.

Homologous Chromosomes

Pairs of matching paternal and maternal chromosomes carrying the same genes at the same loci, although they may carry different alleles.

Allele

A specific sequence variant of a gene denoted by letters, categorized as dominant (capitalized) or recessive (lowercase).

Sister Chromatids

Two identical copies of a replicated chromosome synthesized during $S$ phase that are temporarily joined together by a centromere until separation in mitosis or meiosis II.

Centromere

The constricted chromosomal region that tethers sister chromatids together and serves as the attachment site for spindle microtubules.

Prophase (Mitosis)

The first phase of mitosis characterized by chromosome condensation into distinct $X$-shapes, nuclear membrane disintegration, centrosome migration to opposite poles, and mitotic spindle polymerization.

Metaphase (Mitosis)

The mitotic stage where all $46$ replicated chromosomes align in a single linear row along the equatorial metaphase plate, each linked to spindle fibers from opposite poles.

Anaphase (Mitosis)

The mitotic stage where sister chromatids are pulled apart toward opposite cellular poles by depolymerizing spindle microtubules.

Telophase (Mitosis)

The final mitotic stage marked by dismantling of the mitotic spindle, reformation of nuclear envelopes around each set of $46$ chromosomes, and chromosome decondensation.

Cleavage Furrow

An indentation that deepens like a drawstring around the former spindle midpoint during animal cell cytokinesis, driven by a contractile ring of actin microfilaments.

Cyclins

Phase-specific regulatory proteins whose concentrations rise and fall during the cell cycle to activate cyclin-dependent kinases (CDKs) before being degraded by proteasomes.

Cyclin-Dependent Kinases (CDKs)

Enzymes that remain at constant levels throughout the cell cycle and require binding by specific cyclins to phosphorylate and activate target proteins required for cycle progression.

p53

A tumor suppressor protein known as the 'Guardian of the Genome' that surveys DNA integrity at checkpoints, activating CDK inhibitors, launching repair enzymes, or initiating apoptosis when damage is irreparable.

Apoptosis

Programmed cell death executed when a cell encounters critical, irreversible cellular stresses or extensive genomic damage.

Mutagen

An environmental agent—classified as physical (e.g., UV radiation, X-rays), chemical (e.g., cigarette smoke, nitrates), or biological (e.g., HPV, H. pylori)—that increases mutation frequency.

Somatic Mutation

A non-heritable mutation occurring in non-germline body cells, affecting only the individual organism's tissues.

Germline Mutation

A heritable permanent alteration in the DNA of gametes or reproductive cells, transmitting the mutation to offspring.

Tumor Suppressors

Negative regulatory genes of the cell cycle (acting as 'brakes' or 'security', such as p53 and BRCA1/2) whose loss-of-function mutations disable cell cycle checkpoints.

Proto-oncogenes

Positive regulatory genes that drive cell cycle progression (acting as the 'gas' or 'drivers'); when mutated into oncogenes, they cause uncontrolled checkpoint bypass.

Malignant Tumor

A cancerous mass of cells that invades surrounding tissues and metastasizes by spreading to distant healthy organs.

Benign Tumor

A non-cancerous, localized, and contained mass of cells (such as a lipoma) that does not metastasize, though it may cause local mechanical compression.

Meiosis

A specialized reductional division of germline cells in sexually reproducing eukaryotes that yields four genetically distinct haploid ($1n$) gametes from one diploid ($2n$) parent cell through two successive divisions.

Reductional Division

The first meiotic division (Meiosis I) that halves chromosome ploidy from diploid ($46$ chromosomes / $23$ pairs) to haploid ($23$ replicated chromosomes) by separating homologous chromosomes.

Equational Division

The second meiotic division (Meiosis II) which separates sister chromatids without altering ploidy, maintaining $23$ individual chromosomes per gamete.

Synapsis

The pairing of maternal and paternal homologous chromosomes into four-chromatid complexes called tetrads during Prophase I of meiosis.

Crossing Over

The reciprocal exchange of genetic segments between non-sister chromatids of homologous chromosomes during Prophase I, producing novel hybrid recombinant chromosomes.

Law of Independent Assortment

Mendel's principle stating that alleles on different non-homologous chromosomes distribute into gametes independently, established by the random equatorial positioning of maternal and paternal homologs during Metaphase I.

Law of Segregation

Mendel's principle stating that the two alleles for a given gene separate during gamete formation so each gamete carries only one allele, physically carried out during Anaphase I and Anaphase II.

Metaphase I

The meiotic stage where homologous chromosome pairs align side by side as tetrads along the metaphase plate in two parallel lines of $23$ pairs.

Anaphase I

The stage of Meiosis I where homologous chromosome pairs are pulled apart to opposite poles while sister chromatids stay united at their centromeres.

Metaphase II

The meiotic stage in haploid cells where individual replicated chromosomes align in a single column of $23$ along the metaphase plate with spindle fibers affixed to sister chromatids.

Anaphase II

The stage of Meiosis II where centromeres divide and sister chromatids are pulled apart to opposite cellular poles as single-stranded individual chromosomes.

Polar Bodies

Non-viable, minute haploid daughter cells resulting from unequal cytoplasmic division during female oogenesis that eventually undergo apoptosis.

Random Fertilization

The stochastic fusion of any one unique sperm with any one unique ovum out of over $70\text{ trillion}$ potential combinations ($2^{23} \times 2^{23} = 2^{46}$), generating massive genetic diversity.