CELL DIVISION – CYTOKINESIS

What is cytokinesis and when does it occur?

Division of the cytoplasm following nuclear division (karyokinesis); occurs after mitosis or meiosis.

What structure ensures equal chromosome distribution during division?

The division spindle, made of microtubules between cell poles.

What are chromosomes made of?

Protein + one DNA molecule; carry genomic info from cell to cell.

What forms at the centromere for spindle attachment?

Kinetochores – protein complexes that bind spindle microtubules.

What is the role of the centrosome in cell division?

Organizes microtubules; initiates the formation of the division spindle.

What are telomeres?

Stabilizing ends of chromosomes that protect DNA from degradation.

How many chromosomes and DNA molecules are found in human cells?

Somatic cells: 46 chromosomes (2n)

Gametes: 23 chromosomes (n)

Define chromatid.

One of two identical DNA copies joined at a centromere in a replicated chromosome.

What is the cell cycle?

The cycle of a single cell division alternated with interphase;

includes G1, S, G2, and M phases.

What are the three phases of interphase?

• G1 – cell growth, RNA/protein synthesis

• S – DNA replication (2n → 4n)

• G2 – final protein synthesis before mitosis

What happens in G0 phase?

A resting phase where cells exit the cycle; may be temporary or permanent.

During which phase is DNA content doubled from 2n to 4n?

S phase – DNA replication occurs

What happens in G2 phase?

RNA and protein synthesis continues; cell prepares for mitosis.

How long does a full cell cycle take in human cells?

10–25 hours; mitosis lasts ~1 hour.