Overview
This lecture explains the cell cycle, its stages, and the connection with mitosis as the process by which cells divide and enable growth, repair, and development.
Cell Cycle Overview
- The cell cycle is the process where a cell grows, duplicates its DNA, and divides to form two daughter cells.
- The main purpose of the cell cycle is cell growth, development, and tissue repair.
Main Stages of the Cell Cycle
- The cell cycle consists of two core stages: interphase and the mitosis (M) phase.
- Mitosis (cell division) is the shortest stage of the cycle, while interphase is the longer preparatory stage.
Interphase
- Interphase consists of three phases: G1 (first gap), S (synthesis), and G2 (second gap).
- G1 phase: cell grows and produces proteins and organelles.
- S phase: cell synthesizes a complete copy of its DNA.
- G2 phase: cell prepares for division by duplicating centrosomes and other organelles; chromosomes are not yet visible.
Mitosis (M Phase) Stages
- Mitosis is divided into five phases: prophase, prometaphase, metaphase, anaphase, and telophase, followed by cytokinesis.
- Prophase: chromatin condenses into visible chromosomes, nucleolus disappears, spindle forms, and centrosomes move apart.
- Prometaphase: nuclear envelope fragments, microtubules attach to kinetochores on chromosomes, chromosomes condense further.
- Metaphase: chromosomes align at the metaphase plate; kinetochore microtubules connect to opposite spindle poles.
- Anaphase: cohesins split, sister chromatids separate and move to opposite poles, cell elongates.
- Telophase: new nuclear membranes form around chromosomes at each pole, nucleoli reappear, chromosomes decondense.
Cytokinesis
- Cytokinesis is the division of the cytoplasm, usually starting during telophase.
- In animal cells, a cleavage furrow forms to split the cell into two daughter cells.
Key Terms & Definitions
- Cell cycle — series of events in which a cell grows, duplicates its DNA, and divides.
- Interphase — preparatory phase divided into G1, S, and G2 where the cell grows and duplicates DNA.
- Mitosis — process of nuclear division, resulting in two identical daughter nuclei.
- Cytokinesis — division of the cell’s cytoplasm, producing two separate daughter cells.
- Centrosome — organelle that organizes microtubules and is duplicated before mitosis.
- Chromatid — each of the two identical halves of a duplicated chromosome.
- Kinetochore — protein structure at the centromere where spindle fibers attach.
- Metaphase plate — imaginary plane where chromosomes align during metaphase.
Action Items / Next Steps
- Watch the introductory video on mitosis if not yet viewed.
- Review and clarify any unclear concepts as needed.