Cell Division, Mitosis, Meiosis, and Cell Cycle Control

Vocabulary practice flashcards generated from lecture notes covering cell cycle phases, checkpoints, mitosis, meiosis, chromosomal trisomies, monosomies, and cancer genetics.

Cell Division

The process by which one parent cell produces new cells, essential for growth, repair of damaged tissues, replacement of worn-out cells, and reproduction.

Cell Cycle

The ordered sequence of events that prepares a cell for division and results in two daughter cells, divided into Interphase and Mitotic Phase (M Phase).

Interphase

The phase occupying about $90\%$ of the cell cycle during which the cell grows, performs normal functions, duplicates DNA, and prepares for division.

$G_1$ Phase (First Gap)

The first part of interphase where the cell increases in size, organelles multiply, proteins are synthesized, energy is stored, and normal metabolism occurs.

S Phase (Synthesis)

The phase of interphase where DNA is replicated so each chromosome consists of two identical sister chromatids, and centrosomes duplicate.

$G_2$ Phase (Second Gap)

The final stage of interphase where the cell continues growing, DNA is checked for errors, and proteins needed for mitosis are synthesized.

$G_0$ Phase

A resting stage outside the active cell cycle entered by cells (such as neurons and cardiac muscle cells) that usually no longer divide.

Karyokinesis

The stage of the mitotic phase involving the division of the cell nucleus.

Cytokinesis

The division of the cytoplasm that completes cell division.

$G_1$ Checkpoint

An internal quality-control checkpoint that checks if the cell is large enough, if nutrients are available, and if DNA is damaged before allowing S phase entry or pushing the cell to $G_0$.

$G_2$ Checkpoint

An internal checkpoint that verifies whether DNA has been completely copied and is undamaged before permitting mitosis to begin.

M Checkpoint (Spindle Checkpoint)

An internal checkpoint that verifies whether all chromosomes are properly attached to spindle fibers before anaphase can begin.

Cyclins

Regulatory proteins whose concentration rises and falls predictably during specific phases of the cell cycle.

Cyclin-Dependent Kinases (CDKs)

Enzymes activated by cyclins that phosphorylate target proteins to trigger progression through phases of the cell cycle.

Mitosis

Nuclear division that produces two genetically identical diploid ($2n$) daughter cells.

Prophase

The first stage of mitosis in which chromatin condenses into visible chromosomes, the nucleolus disappears, the nuclear envelope begins breaking down, centrosomes move apart, and spindle fibers form.

Prometaphase

The stage of mitosis where the nuclear envelope completely disappears, kinetochores form, spindle fibers attach to kinetochores, and chromosomes move toward the cell center.

Metaphase

The stage of mitosis where maximally condensed chromosomes align at the metaphase plate with spindle fibers fully attached from opposite poles.

Anaphase

The stage of mitosis where cohesin proteins break down, sister chromatids separate into individual chromosomes, and move toward opposite poles.

Telophase

The stage of mitosis where chromosomes reach opposite poles, uncoil, nuclear envelopes reform around each set, and spindle fibers disappear.

Cleavage Furrow

A structure formed in animal cells during cytokinesis by a contractile ring of actin that pinches the cell into two daughter cells.

Cell Plate

A structure formed from Golgi vesicles in plant cells during cytokinesis that develops into a new cell wall between daughter cells.

Nondisjunction

The failure of sister chromatids to separate properly during cell division, producing daughter cells with abnormal chromosome numbers ($n + 1$ and $n - 1$).

Down Syndrome (Trisomy 21)

A condition caused by having three copies of chromosome $21$ instead of two, characterized by short neck, flattened facial profile, small mouth, and upward slanting eyes.

Edward Syndrome (Trisomy 18)

A disorder caused by an additional copy of chromosome $18$, leading to physical manifestations such as clenched fists, cleft palate, low-set ears, and severe defects of internal organs.

Patau Syndrome (Trisomy 13)

A disorder caused by an additional copy of chromosome $13$, resulting in physical manifestations like extra fingers or toes (polydactyly), cleft lip or palate, and small head size.

Klinefelter Syndrome ($47\text{, XXY}$)

A condition in males resulting from two or more X chromosomes, primarily causing infertility and small, poorly functioning testicles.

Trisomy X Syndrome ($47\text{, XXX}$)

A condition characterized by an extra X chromosome in each cell of a female, often resulting in taller stature and mild or absent physical symptoms.

Turner Syndrome ($45\text{, XO}$)

A condition affecting females caused by a missing or partially missing X chromosome, leading to short stature, webbed neck, and swollen hands and feet.

Mosaicism

A condition occurring when a mutation arises during mitosis in an early embryonic cell, resulting in an organism containing a mix of normal and mutated cells in different tissues.

Cancer

A disease in which cells lose normal control over the cell cycle, leading to uncontrolled cell growth, division, and avoidance of apoptosis.

Proto-oncogenes

Normal genes that promote cell growth and division essential for normal development.

Oncogenes

Mutated forms of proto-oncogenes that continuously stimulate cell division even in the absence of normal growth signals.

p53 Protein

Known as the Guardian of the Genome, a protein that detects DNA damage to stop the cell cycle, activate DNA repair, or initiate apoptosis if repair fails.

Tumor Suppressor Genes

Genes (such as p53, Rb, and p21) that slow or stop the cell cycle, repair DNA damage, and trigger apoptosis to prevent uncontrolled cell growth.

p21 Protein

A protein activated by p53 that blocks cyclin-dependent kinases (CDKs), halting the cell in $G_1$ phase until DNA repair is completed.

Apoptosis

Controlled or programmed cell death that safely eliminates damaged, infected, or unnecessary cells without triggering inflammation.

Benign Tumor

A non-cancerous mass of abnormal cells that does not invade surrounding tissues and remains localized.

Malignant Tumor

A cancerous mass of abnormal cells that invades nearby tissues and can metastasize to other body parts.

Metastasis

The process by which malignant cancer cells spread from their primary location to distant parts of the body through blood or lymph.

Meiosis

A two-step nuclear division process that reduces a diploid ($2n$) cell to four genetically distinct haploid ($n$) gametes (sperm or egg cells).

Crossing Over

The process during prophase I of meiosis where homologous chromosomes pair up and exchange genetic segments.

Synaptonemal Complex

A protein structure that holds homologous chromosomes together during crossing over in meiosis I.

Chiasmata

Cross-shaped structures visible under a microscope where homologous chromosomes remain linked after crossing over and synaptonemal complex breakdown.