Cell Reproduction and Interphase

Study Notes

Cells reproduce through a process called the cell cycle.
The cell cycle is divided into four stages: G1, S, G2, and M.
G1, S, and G2 comprise interphase, the period when the cell is not dividing.
Mitosis occurs during the M phase and involves chromosome duplication followed by separation, ultimately creating two identical daughter cells.
Interphase, specifically the G1 phase, is the longest phase, where the cell determines whether to duplicate its chromosomes or exit the cell cycle.

G1: Growth and synthesis; begins after mitosis and cytokinesis end. The cell grows and prepares for DNA replication.
G1: The longest phase. The cell determines if it will duplicate its chromosomes, committing to the S phase or leaving the cell cycle.
S: Chromosomes duplicate, creating a pair of sister chromatids joined at a centromere. In animal cells, the centriole pairs are also replicated.
G2: The cell prepares for division including final preparations for mitosis.

Mitosis is the process by which a eukaryotic cell divides its chromosomes into two identical sets.
Mitosis is followed by cytokinesis, the division of the cytoplasm and organelles, resulting in two separate daughter cells.
Mitosis is divided into four phases: prophase, metaphase, anaphase, and telophase (PMAT). These phases ensure accurate distribution of chromosomes to the daughter cells.
Daughter cells are genetically identical.

Growth of an organism by increasing the size or number of cells.
Replacement of damaged or dying cells. This is essential in various parts of the body, tissues, like skin and the digestive tract for continuous renewal and repair.
Regeneration, in which some organisms (sea stars, lizards, and lobsters) can regrow lost body parts.
Asexual reproduction in various organisms (hydra, sponges, planaria). This results in genetically identical offspring.

Prophase:
Nuclear membrane and nucleolus disappear.
Chromatin condenses into chromosomes.
Chromosomes have two sister chromatids bound at the centromere.
Centrioles create spindle fibers that align with kinetochores on chromosomes.
Chromosomes are visible under a microscope.
Metaphase:
- Spindle fibers attach to chromatids.
- Chromosomes line up down the middle of the cell forming “the metaphase plate”.
- This organization ensures an equal distribution of chromosomes to each daughter cell.
Anaphase:
- Sister chromatids split and become separate daughter chromosomes.
- Spindle fibers pull the chromosomes to opposite ends of the cell. Centromeres split.
Telophase:
- Spindle fibers continue pulling chromosomes.
- Nuclear membranes form around both sets of chromosomes and begin to break up the chromosomes.
- Chromosomes become less condensed.
- Mitosis is complete at this point.

Preprophase stage, a sheet of cytoplasm (phragmosome) bisects the cell where the division will occur.
Centrioles are not present.
Cytokinesis occurs by formation of a cell plate.