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Cell Cycle Regulators

control when a cell grows, copies its DNA, and divides.

Cyclins

Proteins whose levels rise and fall during the cell cycle. They activate cyclin-dependent kinases (CDKs) to move the cell from one phase to the next.

Cyclin-Dependent Kinases (CDKs)

Enzymes that become active only when attached to cyclins.

Cell Cycle Checkpoints

Surveillance mechanisms that monitor the condition of the cell and ensure that each phase of the cell cycle is completed accurately before the next phase begins.

G₁ Checkpoint

The checkpoint between the G₁ and S phases where the cell evaluates its size, nutrient availability, growth signals, and DNA integrity before DNA replication begins.

G₂ Checkpoint

The checkpoint between the G₂ and M phases that verifies whether DNA replication has been completed accurately and checks for DNA damage before mitosis begins.

M Checkpoint

The checkpoint during metaphase that ensures all chromosomes are properly attached to spindle fibers before the sister chromatids separate during anaphase.

Tumor Suppressor Genes

Genes that produce proteins responsible for regulating cell division, repairing damaged DNA, and preventing uncontrolled cell growth.

p53

A tumor suppressor protein encoded by the TP53 gene that regulates the cell cycle by detecting DNA damage, pausing cell division for repair, or initiating apoptosis if the damage is irreparable.

Growth Factors

Naturally occurring signaling proteins that stimulate cell growth, proliferation, differentiation, and survival by binding to specific receptors on the cell surface.

Apoptosis

A genetically programmed process of controlled cell death that eliminates damaged, infected, or unnecessary cells without causing inflammation.

G₁ Phase (Gap 1)

The first stage of interphase during which the cell grows, carries out normal metabolic activities, and synthesizes proteins and organelles needed for DNA replication.

S Phase (Synthesis)

The phase of interphase during which the cell replicates its DNA, resulting in duplicated chromosomes.

G₂ Phase (Gap 2)

The final stage of interphase during which the cell continues to grow, synthesizes proteins required for mitosis, and checks the accuracy of DNA replication.

M Phase (Mitotic Phase)

The phase of the cell cycle during which the nucleus divides by mitosis and the cytoplasm divides by cytokinesis, producing two genetically identical daughter cells.

G₀ Phase

A resting state in which cells exit the cell cycle and stop dividing, either temporarily or permanently, while carrying out their normal functions.

Prophase (P)

The first stage of mitosis in which chromatin condenses into visible chromosomes, the nuclear envelope begins to break down, and the mitotic spindle starts to form.

Metaphase (M)

The second stage of mitosis in which chromosomes align along the cell's equator (metaphase plate) and spindle fibers attach to the centromeres.

Anaphase (A)

The third stage of mitosis in which sister chromatids separate and are pulled by spindle fibers toward opposite poles of the cell.

Telophase (T)

The final stage of mitosis in which chromosomes reach opposite poles, decondense into chromatin, and new nuclear envelopes form around each set of chromosomes.

Cytokinesis (Occurs After Mitosis)

The division of the cytoplasm that produces two separate daughter cells.

Chromatin

The uncoiled form of DNA found in the nucleus during interphase.

Chromosome

A condensed structure made of DNA and proteins that carries genetic information.

Spindle Fibers

Microtubule fibers that separate chromosomes during cell division.

Centrosome

The organelle that organizes spindle fibers during mitosis.

Centrioles

Cylindrical structures found mainly in animal cells that help organize the spindle fibers.

Mitosis

pocess of nuclear division in eukaryotic cells that produces two genetically identical daughter nuclei

Meiosis

is a specialized type of cell division that reduces the chromosome number by half, producing four genetically unique haploid daughter cells (gametes) from one diploid parent cell.

Prophase I

The first stage of Meiosis I in which chromosomes condense, homologous chromosomes pair up (synapsis), crossing over occurs, and the spindle apparatus forms.

Synapsis

The pairing of homologous chromosomes during Prophase I.

Homologous Chromosomes

A pair of chromosomes, one inherited from each parent, that have the same genes at corresponding locations but may carry different alleles.

Tetrad

A structure formed when two homologous chromosomes pair during Prophase I, consisting of four chromatids.

Crossing Over

The exchange of genetic material between non-sister chromatids of homologous chromosomes during Prophase I.

Metaphase I

The stage in which homologous chromosome pairs (tetrads) align at the cell's equator.

Anaphase I

The stage in which homologous chromosomes separate and move to opposite poles, while sister chromatids remain attached.

Telophase I

The stage in which homologous chromosomes reach opposite poles, and the cell divides to form two haploid daughter cells.

Cytokinesis I

Division of the cytoplasm after Meiosis I, producing two haploid cells.

Meiosis II (Equational Division)

The second division of meiosis in which sister chromatids separate, producing four haploid daughter cells.

Prophase II

Chromosomes condense again, the nuclear envelope breaks down (if it reformed), and spindle fibers form.

Metaphase II

Chromosomes align individually at the metaphase plate.

Anaphase II

Sister chromatids separate and move toward opposite poles.

Telophase II

Chromosomes arrive at opposite poles, nuclear envelopes reform, and cytokinesis produces four genetically different haploid cells.

Cytokinesis II

Division of the cytoplasm that results in four haploid daughter cells.

Gamete

A haploid reproductive cell (sperm or egg) produced by meiosis.

Haploid (n)

A cell containing one set of chromosomes.

Diploid (2n)

A cell containing two sets of chromosomes, one from each parent.

Genetic Variation

Differences in DNA among individuals of the same species.