The Cell Cycle & Mitosis

Interphase

The bulk of a cell's life cycle (G1, S, G2) where it grows and replicates DNA, but is NOT actively dividing.

Chromatin

The loose, uncoiled form of DNA present during Interphase, allowing machinery to access genes for transcription.

Cell Cycle: G1 Phase

Phase for cell growth and organelle synthesis.

Cell Cycle: S Phase

Phase for DNA replication. Chromosomes duplicate to form identical sister chromatids.

Cell Cycle: G2 Phase

Phase following DNA replication where the cell continues to grow and double-checks for replication errors before dividing.

Cell Cycle: M Phase

The phase where active cell division (Mitosis and Cytokinesis) occurs.

G1/S Checkpoint (Restriction Point)

Heavily regulated by p53. If DNA is damaged, the cycle arrests for repair or initiates apoptosis before replication.

p53 Protein

The master tumor suppressor protein that monitors DNA integrity at the G1/S checkpoint.

Cyclins & CDKs

Regulatory molecules of the cell cycle. Cyclins bind Cyclin-Dependent Kinases to phosphorylate transcription factors.

Oncogenes

Mutated genes that actively promote rapid, unchecked cell division (stepping on the gas).

Tumor Suppressor Genes

Genes (like p53 and Rb) that normally halt the cell cycle or trigger apoptosis. Mutations cause a loss of function (cutting the brakes).

Diploid (2n)

A cell containing two complete sets of chromosomes (one maternal, one paternal).

Mitosis: Prophase

Chromatin condenses into visible chromosomes, the nuclear envelope dissolves, and the mitotic spindle forms.

Centrioles

Cylindrical organelles that migrate to opposite poles of the cell during Prophase to form the mitotic spindle.

Mitosis: Metaphase

Spindle fibers align chromosomes single-file along the metaphase plate (cell equator).

Metaphase Plate

The equator of the cell where chromosomes perfectly align during Metaphase.

Mitosis: Anaphase

Centromeres split; sister chromatids are ripped apart and pulled to opposite poles.

Mitosis: Telophase

Nuclear envelopes reform around the two new sets of DNA, and chromosomes uncoil.

Centromere

The central region of a chromosome that holds two sister chromatids together.

Kinetochore

The protein structure on the centromere where microtubule spindle fibers physically attach during cell division.

Sister Chromatids

Identical copies of a single chromosome created during S phase. Separated during Mitosis and Meiosis II.

Cytokinesis

The physical separation of the cytoplasm and organelles into two distinct daughter cells.