Cell Cycle, Chromosome Structure, and Mitosis

Comprehensive vocabulary flashcards covering chromosome architecture, stages of the eukaryotic cell cycle, mitotic division, cytokinesis, cell cycle checkpoints, and genetic cancer mechanisms.

Septum

A ring of proteins that contracts to split the cytoplasm and divide a cell in half during cellular division.

Diploid ($2n$)

The state of possessing two complete sets of chromosomes; in humans, the diploid number is $46$ ($23$ from each parent).

Haploid

One complete set of chromosomes required to be considered a species; in humans, the haploid number is $23$ and is found exclusively in reproductive sex cells (egg and sperm cells).

Homologous Chromosomes

Pairs of chromosomes inherited from maternal and paternal contributions that serve as matched copies of genetic instructions.

Karyotype

An individual's unique arrangement of chromosomes, characterized by an $XY$ chromosome pair in biological males and an $XX$ chromosome pair in biological females.

Chromosome

A single uninterrupted piece of $DNA$ structured on a protein scaffold.

Chromatin

The primary structure of a chromosome consisting of $DNA$ wrapped around scaffold proteins.

Nucleosomes

Bundles of chromatin resembling 'beads on a string' that demonstrate the compact organization of $DNA$.

Histones

Proteins that regulate access to the genome by opening up or locking away specific regions of $DNA$ to permit or silence gene expression.

Topologically Associated Domains (TADs)

Regions within chromosomes where specific areas of $DNA$ interact with each other to make cellular processes more efficient or functionally possible.

Heterochromatin Domains

Regions of the genome that are condensed and not actively being expressed by the cell.

Euchromatin Domains

Sections of the genome that are uncoiled and actively being expressed.

Sister Chromatids

An $X$-shaped structure composed of an original chromosome duplicated onto itself, held together for cell division.

Centromere

The internal binding point on a chromosome where cohesion proteins attach to keep sister chromatids joined together.

Cohesion Proteins

Proteins that bind at the centromere to hold sister chromatids together so they can be split evenly during division.

Kinetochores

External docking structures on chromosomes that act like trailer hitches for spindle fibers to attach and physically move the chromosomes.

Interphase

The longest portion of the eukaryotic cell cycle, comprising $G_1$, $S$, and $G_2$ phases, during which $DNA$ remains diffused and the cell performs daily functions while preparing for division.

$S$ Phase

The synthesis phase of interphase during which the cell replicates its genome, converting $46$ chromosomes into $46$ sister chromatids ($92$ individual chromosomes).

Centrioles

Cellular structures that form during interphase and function as part of the machinery for chromosome division in animal cells.

Prophase

The first phase of mitosis marked by three events: chromosomes condense and become visible, the nuclear envelope dissolves, and spindle fibers form.

Spindle Fibers

Structures composed of the same protein material as the dissolved nucleus that attach to kinetochores to pull and manipulate chromosomes in space.

Prometaphase

The stage of mitosis where spindle fibers attach to the kinetochores on the sister chromatids.

Metaphase

The mitotic phase where all $46$ sister chromatids line up in a single plane across the center of the cell.

Metaphase Plate

The cellular equator along which chromosomes align during metaphase, dividing the cell into two equal hemispheres.

Anaphase

The phase of mitosis in which sister chromatids are pulled apart to opposite poles, reverting to individual chromosomes.

Telophase

The phase of mitosis considered the reversal of prophase, wherein two new nuclei reform, chromosomes uncoil into an invisible state, and spindle fibers break down.

Cytokinesis

The process occurring concurrently with telophase that divides the cytoplasm, splitting the parent cell into two separate daughter cells.

Cleavage Furrow

The indentation created in animal cells during cytokinesis as a band of protein contracts around the center to pinch the cytoplasm in two.

Cell Plate

The partition structure formed between dividing plant cells during cytokinesis that develops into a new cell wall.

$G_1/S$ Checkpoint

The initial cell cycle stopgap that assesses whether the cell has grown large enough and is prepared to duplicate its genome.

$G_2/M$ Checkpoint

The regulatory checkpoint where the cell commits to initiating mitotic cell division.

Spindle Checkpoint

The irreversible checkpoint ensuring that all chromosomes are accurately copied, properly aligned, and fully attached to spindle fibers before proceeding to anaphase.

Proto-oncogenes

Normal cellular genes that help prevent uncontrolled division and cell death, which can mutate into cancer-promoting oncogenes.

Oncogenes

Mutated genes that cause uncontrolled cell proliferation and can lead to metastatic tumor development.

Tumor Suppressor Genes

Protective genes that prevent abnormal cellular growth; both copies must be corrupted or knocked out for cancer-like uncontrolled behavior to arise.

Alleles

Alternative forms of the same gene that determine different expressions of a particular genetic trait.