Genomes, the Cell Cycle, Mitosis, and Meiosis

Vocabulary flashcards covering genome packaging, chromosome structure, cell cycle stages, mitotic phases, checkpoints, molecular regulators, cancer genetics, and meiosis.

Genome

The complete set of genetic material ($\text{DNA}$) present in a cell or organism.

Nucleoid

The central cytoplasmic region in a prokaryotic cell where the single double-stranded, circular $\text{DNA}$ molecule resides.

Plasmids

Additional smaller, circular loops of $\text{DNA}$ that may be present in prokaryotic cells.

Nucleosome

The fundamental subunit of chromatin packaging, consisting of a short stretch of $\text{DNA}$ wrapped around a core of 8 histone proteins.

Linker DNA

The connecting string of $\text{DNA}$ located between adjacent nucleosomes.

Chromatin

The structural complex of a single long double helix of $\text{DNA}$ wrapped around proteins called histones.

Gene

A section of $\text{DNA}$ located on a chromosome that contains instructions to build a particular protein.

Sister Chromatids

Two identical copies of a replicated chromosome joined at the centromere, possessing identical nucleotide sequences.

Centromere

The specialized region of a chromosome where two sister chromatids are closely attached to each other.

Somatic Cells

Typical body cells containing two matched sets of chromosomes, making them diploid ($2n$).

Gametes

Reproductive sex cells (eggs and sperm) that possess half the somatic chromosome number and are haploid ($1n$).

Karyotype

An individual's complete set of chromosomes, or an organized visual representation of those chromosomes.

Homologous Chromosomes

Chromosome pairs of the same length, shape, and gene loci that contain the same genetic content, with one member inherited from each parent.

Heterologous Chromosomes

Chromosome pairs that exhibit different physical structures and different genetic content, such as human sex chromosomes ($X$ and $Y$).

The Cell Cycle

An orderly series of events describing the life of a cell from the division of a single parent cell to the production of two new genetically identical daughter cells.

Interphase

The major portion of the cell cycle dedicated to normal cellular growth and preparation for cell division, composed of $G_1$, $S$, and $G_2$ stages.

$G_1$ Phase

The first gap phase of interphase, during which the cell grows, synthesizes macromolecules, and accumulates biochemical energy.

$S$ Phase

The synthesis stage of interphase during which chromosomal $\text{DNA}$ is completely replicated.

$G_2$ Phase

The second gap stage of interphase where energy reserves are replenished, organelles duplicate, and the cytoskeleton breaks down.

Karyokinesis

The first step of the mitotic phase involving nuclear division (also known as mitosis).

Cytokinesis

The second stage of the mitotic phase during which the cytoplasmic components physically divide into two daughter cells.

Spindle Apparatus

A cellular structure composed of microtubules originating from microtubule organizing centers (MTOCs) that generates mechanical force to move chromosomes.

Kinetochore

A protein complex situated at a specific portion of the centromere that serves as the attachment point for spindle microtubules.

Astral Microtubules

Spindle microtubules that interact with proteins in the plasma membrane to anchor and hold the microtubule organizing centers (MTOCs) in place.

Cleavage Furrow

A constricting groove produced by an actin-myosin contractile ring that pinches the plasma membrane during cytokinesis in animal cells.

Cell Plate

A membrane-bound structure formed by coalescing Golgi vesicles at the metaphase plate in dividing plant cells that leads to the formation of a new cell wall.

$G_0$ State

A quiescent, non-dividing arrested state entered by cells that exit the cell cycle during $G_1$.

$G_1$ Checkpoint

A restriction point determining whether external cues, adequate cell reserves, cell size, and genomic $\text{DNA}$ integrity are sufficient for entry into $S$ phase.

$G_2$ Checkpoint

A cell cycle checkpoint prior to mitosis that halts the cycle if chromosomes are not fully replicated or if $\text{DNA}$ damage is detected.

$M$ Checkpoint

The spindle checkpoint occurring near the end of metaphase that ensures all sister chromatid kinetochores are securely attached to spindle microtubules.

Positive Regulators

Intracellular regulatory molecules, such as cyclins and CDKs, that promote advancement of the cell cycle to the next step.

Negative Regulators

Intracellular regulatory proteins (such as Rb, p53, and p21) that halt or prevent progression through the cell cycle.

Cyclin-Dependent Kinases (CDKs)

Enzymes that phosphorylate and activate target proteins critical for cell cycle advancement when bound to a specific cyclin partner.

Cyclins

Regulatory proteins that bind and activate CDKs, whose cellular concentrations fluctuate predictively throughout the cell cycle.

Maturation-Promoting Factor (MPF)

A positive regulatory complex composed of cyclin B and a CDK that triggers passage through the $G_2$ checkpoint into $M$ phase.

Retinoblastoma Protein (Rb)

A negative regulatory tumor suppressor protein that prevents cell progression past the $G_1$ checkpoint until phosphorylated.

p53

A tumor suppressor protein acting at the $G_1$ checkpoint that arrests the cell cycle for $\text{DNA}$ repair or triggers apoptosis if damage is irreparable.

Proto-Oncogenes

Normal genes that code for positive cell cycle regulator proteins; when mutated inappropriately, they can become cancer-causing oncogenes.

Oncogenes

Mutated forms of proto-oncogenes that stimulate accelerated, unregulated cellular reproduction.

Tumor Suppressor Genes

Segments of $\text{DNA}$ coding for negative regulator proteins that inhibit unregulated cell division.

Asexual Reproduction

A mode of reproduction involving a single parent that produces clonal offspring genetically identical to the parent and to each other.

Sexual Reproduction

A reproductive strategy involving two parents that generates genetically distinct offspring by shuffling parental chromosomes.

Fertilization

The union of two haploid gametes (egg and sperm) to create a single diploid zygote ($2n$).

Allele

A specific alternative form or sequence variant of a gene found at a given chromosomal location.

Ploidy

The number of complete sets of chromosomes present within a cell of an organism.

Meiosis

A specialized double-division nuclear process that halves the chromosome number from diploid ($2n$) to haploid ($1n$) to produce gametes or spores.

Synaptonemal Complex

A protein matrix that holds paired homologous chromosomes tightly together in synapsis during prophase I of meiosis.

Crossing Over

The reciprocal exchange of genetic segments between non-sister chromatids of a homologous pair during prophase I of meiosis.

Chiasmata

X-shaped visible connection points where non-sister chromatids have exchanged genetic material and remain held together.

Tetrad

A four-chromatid structure composed of two paired homologous chromosomes joined together by chiasmata during prophase I.

Reduction Division

The first division of meiosis (meiosis I) wherein homologous chromosome pairs separate, reducing the ploidy from diploid ($2n$) to haploid ($1n$).