Cell Cycle, Mitosis, Meiosis, and Molecular Inheritance

Comprehensive vocabulary flashcards covering the cell cycle, mitosis, meiosis, chromosome structure, genetic mutations, and molecular inheritance based on lecture notes.

Centromere

The narrow "waist" of a duplicated chromosome where two sister chromatids are held together and where the kinetochore protein complex attaches.

Telomeres

Protective, non-coding, repetitive nucleotide "caps" (such as $TTAGGG$ in humans) located at the ends of linear eukaryotic chromosomes that prevent the loss of critical genes during repeated DNA replication.

Homologous Chromosomes

A pair of chromosomes in diploid eukaryotic cells—one inherited from the mother and one from the father—that carry genes controlling the same inherited characters at corresponding loci, though they may have different alleles or traits.

Karyotype

An ordered, photographic display of an individual's complete set of homologous chromosome pairs, arranged by size, centromere position, and banding pattern.

Autosomes

Chromosomes that do not determine the biological sex of an organism; in humans, these make up chromosome pairs $1$ through $22$.

Sex Chromosomes

The $23\text{rd}$ pair of chromosomes ($X$ and $Y$ in humans) that determines the biological sex of an individual, where females typically possess $XX$ and males possess $XY$.

Somatic Cells

All diploid ($2n$) body cells (such as skin, liver, or brain cells) containing two complete sets of chromosomes—one set from each parent.

Gametes

Haploid ($n$) reproductive cells (eggs and sperm) produced through meiosis that carry only one single set of chromosomes.

Cell Theory

The fundamental biological doctrine stating that: (1) the cell is the basic unit of life, (2) all living organisms are composed of one or more cells, and (3) all new cells arise from existing cells.

Interphase

The longest portion of the cell cycle, comprising the $G_1$, $S$, and $G_2$ sub-phases, during which the cell grows, duplicates organelles, and replicates its nuclear DNA in preparation for division.

Sister Chromatids

Two identical copies of a duplicated chromosome produced during the $S$ phase of interphase, joined together at their centromeres by cohesion proteins.

Chromatin

The uncoiled, diffuse complex of DNA and histone proteins found inside the eukaryotic nucleus prior to chromosome condensation.

Mitotic Spindle

A macromolecular structure assembled from microtubules and associated proteins that coordinates chromosome alignment and segregation during mitosis.

Centrosome

The primary microtubule-organizing center of animal cells that replicates during interphase, migrates to opposite cell poles, and nucleates the mitotic spindle fibers.

Kinetochore

A specialized protein structure assembled on the centromere of each chromatid that serves as the attachment site for spindle microtubules.

Prometaphase

The sub-phase of mitosis during which the nuclear envelope disintegrates, allowing spindle microtubules to enter the nuclear region and bind to chromosomal kinetochores.

Metaphase Plate

The imaginary plane equidistant between the two spindle poles where duplicated chromosomes align in a single file during metaphase.

Cleavage Furrow

A shallow contractile ring of microfilaments that pinches animal cell cytoplasm inward at the cell equator during cytokinesis, splitting the parent cell into two daughter cells.

Gap1 Checkpoint

The primary control checkpoint ("Restriction Point") of the cell cycle that evaluates cell size, nutrient availability, DNA integrity, and external growth signals before committing the cell to division.

$$G_0\text{ Phase}$$

A non-dividing, quiescent cell state entered when a cell does not receive a "go-ahead" signal at the $G_1$ checkpoint; common to fully differentiated cells like mature nerve cells.

Cyclins

Regulatory proteins whose intracellular concentrations oscillate predictably throughout specific stages of the cell cycle, activating cyclin-dependent kinases.

Cyclin-Dependent Kinases (Cdks)

Enzymatic proteins that phosphorylate target substrates to drive cell cycle progression, but require association with an appropriate regulatory cyclin protein to become active.

Maturation Promoting Factor (MPF)

A protein complex consisting of a Cyclin-Dependent Kinase (Cdk) and cyclin that triggers the cell to pass the $G_2$ checkpoint and enter mitosis, reaching peak activity at metaphase before cyclin degrades in anaphase.

Density-Dependent Inhibition

An external cell cycle control mechanism in which crowded cells stop dividing once they form a complete monolayer and make contact with one another.

Anchorage-Dependence

The requirement that a normal animal cell must be attached to a substratum (such as the extracellular matrix or another cell) in order to initiate and complete division.

Metastasis

The spread of malignant cancer cells away from their primary tumor site to distant locations in the body via the bloodstream or lymphatic vessels.

Asexual Reproduction

A mode of reproduction wherein a single parent produces genetically identical offspring (clones) without the fusion of gametes, resulting in no genetic variation.

Sexual Reproduction

A process whereby two parents produce haploid gametes through meiosis that unite during fertilization, generating offspring with unique genetic combinations from both parents.

Meiosis

A specialized two-stage nuclear division ($\text{Meiosis I}$ and $\text{Meiosis II}$) that reduces the chromosome number by half from diploid ($2n$) to haploid ($n$), creating four genetically distinct gametes.

Synapsis

The pairing and physical zippering together of homologous chromosomes during prophase I of meiosis to form four-chromatid complexes termed tetrads.

Crossing Over

The reciprocal exchange of genetic material between non-sister chromatids of a homologous pair during prophase I of meiosis, resulting in recombinant chromosomes.

Chiasma

The microscopic $X$-shaped site (plural: chiasmata) representing the physical point of contact where crossing over occurs between non-sister chromatids of homologous chromosomes.

Law of Independent Assortment

The biological principle stating that during metaphase I, each pair of homologous chromosomes (tetrad) orients randomly and independently of all other pairs on the metaphase plate, yielding $2^n$ possible chromosome combinations in gametes.

Random Fertilization

The principle that any single sperm can fuse with any single egg, producing approximately $2^{23} \times 2^{23} \approx 70\text{ trillion}$ diploid genetic combinations in human offspring without factoring in crossing over.

Nondisjunction

An error during cell division in which homologous chromosome pairs fail to separate during anaphase I, or sister chromatids fail to separate during anaphase II, leading to abnormal gamete chromosome counts.

Aneuploidy

A condition in which a zygote has an abnormal number of chromosomes resulting from fertilization involving a gamete that underwent nondisjunction.

Trisomy 21 (Down Syndrome)

An autosomal aneuploid condition caused by nondisjunction resulting in three copies of chromosome $21$, characterized by developmental delays, heart defects, and a life expectancy of approximately $60\text{ years}$.

Turner Syndrome

A sex chromosome monosomy disorder characterized by an $X0$ karyotype in phenotypic females; it is the only known survivable monosomy in humans and most commonly causes sterility.

Klinefelter Syndrome

A sex chromosome disorder in males caused by an extra $X$ chromosome, resulting in an $XXY$ genotype.

Translocation Error

A chromosomal structural mutation occurring when a broken segment of one chromosome reattaches to a non-homologous chromosome.

Inversion Error

A chromosomal structural alteration occurring when a broken chromosome segment reattaches to the exact same chromosome but in an inverted, reverse orientation.

Tetranucleotide Hypothesis

A disproven 1940s hypothesis proposing that DNA is composed of an equal, repeating sequence of the four nitrogenous bases ($AGTC$), which incorrectly led scientists to believe proteins must carry hereditary information.

Hershey-Chase Experiments

A landmark 1952 study by Alfred Hershey and Martha Chase using radioactive sulfur ($^{35}S$) in viral protein coats and radioactive phosphorus ($^{32}P$) in viral DNA to demonstrate that DNA is the genetic material responsible for heredity.

Marie Maynard Daly

A scientist who in 1950 developed pioneering techniques to isolate cell nuclei, quantify base compositions, confirm four distinct bases across species, and investigate histone protein organization.

Chargaff's Rules

The biochemical findings by Edwin Chargaff stating that within an organism's DNA, the amount of adenine equals thymine ($A = T$) and the amount of cytosine equals guanine ($C = G$), with nucleotide composition varying across species.

Semiconservative Model

The mechanism of DNA replication wherein each newly produced double helix contains one intact original parental strand and one newly synthesized daughter strand.

Helicase

An enzyme that breaks hydrogen bonds between nitrogenous base pairs to unwind and separate parental DNA strands at replication forks.

Single-Strand Binding Proteins (SSBP)

Molecules that bind to newly separated single DNA template strands during replication to stabilize them and keep them from prematurely re-annealing.

Topoisomerase

An enzyme positioned ahead of the advancing replication fork that relieves overwinding strain by breaking, swiveling, and rejoining parental DNA strands.

Primase

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

DNA Polymerase III

The primary enzyme in prokaryotic DNA replication that elongates new DNA strands in the $5' \rightarrow 3'$ direction by adding matching nucleotides to the $3'$ end at rates up to $500\text{ nucleotides/second}$ in bacteria and $50\text{ nucleotides/second}$ in humans.

DNA Polymerase I

An enzyme responsible for removing RNA primer nucleotides from nascent strands and replacing them with correct DNA deoxyribonucleotides.

Leading Strand

The continuously synthesized complementary DNA strand that elongates toward the replication fork in the $5' \rightarrow 3'$ direction and requires only a single RNA primer.

Lagging Strand

The discontinuously synthesized DNA strand that elongates away from the replication fork in short segments, requiring multiple RNA primers.

Okazaki Fragments

Short stretches of newly synthesized DNA produced discontinuously along the lagging template strand during DNA replication.

DNA Ligase

An enzyme that facilitates the joining of DNA fragments by catalyzing the formation of covalent phosphodiester bonds, effectively sealing nicks between Okazaki fragments.

Nuclease

An enzyme that excises segments of damaged, deformed, or incorrectly paired DNA strands so that DNA Polymerase and DNA Ligase can replace them with correct nucleotides.

Telomerase

An enzyme active in germ cells and many cancer cells that catalyzes the lengthening of telomeres, allowing unlimited cell divisions by preventing chromosome shortening.