Cell Division and the Cell Cycle

Study Notes

Cell Division and the Cell Cycle

Cell division is the process by which organisms produce more of their own kind.
Rudolf Virchow proposed the concept of "Omnis cellula e cellula" meaning all cells arise from pre-existing cells.
Cell division plays crucial roles in reproduction, development, and renewal/repair of cells.
The cell cycle consists of a series of phases that lead to cell division.
Chromosomes are crucial for the distribution of genetic material during cell division.
In eukaryotic cells, chromosomes are organized within the nucleus in a linear structure.
The number of chromosomes varies among species.

Mitosis and Cytokinesis

Mitosis is the division of the genetic material in the nucleus. It is followed immediately by cytokinesis, the division of the cytoplasm.
Mitosis results in two cells that are genetically identical to the parent cell.
Mitosis and cytokinesis produce somatic cells, which are all the cells in the body except for gametes.
Somatic cells have two sets of chromosomes, one set inherited from each parent (diploid).
Gametes (sperm and eggs) have half the number of chromosomes as somatic cells (haploid).

Chromosome Structure and Duplication

When a cell is not dividing, each chromosome is in the form of a long, thin chromatin fiber.
During cell division, chromosomes condense, becoming densely coiled and folded, making them visible under a light microscope.
A duplicated chromosome consists of two sister chromatids.
Sister chromatids are joined together along their lengths by cohesins, protein complexes.
Each sister chromatid has a centromere, a region where it is attached most closely to its sister chromatid.
Sister chromatids separate during cell division, becoming individual chromosomes.
Chromosome duplication and condensation occur during cell division.

Cell Cycle Phases

The cell cycle consists of four main phases:
- G1 (Growth 1): Cell grows and produces proteins and organelles.
- S (Synthesis): DNA replication occurs.
- G2 (Growth 2): Cell prepares for cell division.
- M (Mitotic): Cell divides into two daughter cells.
The duration of each phase can vary depending on the type of cell.
Cells that do not divide frequently or at all can enter the G0 phase, a resting state.

Mitosis Stages

Mitosis is conventionally divided into five stages:
- Prophase: Chromosomes condense, nuclear envelope breaks down, spindle fibers form.
- Prometaphase: Spindle fibers attach to chromosomes, chromosomes move towards the center of the cell.
- Metaphase: Chromosomes align at the metaphase plate, the center of the cell.
- Anaphase: Sister chromatids separate and move towards opposite poles.
- Telophase: Nuclear envelope reforms around chromosomes, chromosomes decondense.
Cytokinesis completes the mitotic phase by dividing the cytoplasm into two daughter cells.

The Mitotic Spindle

The mitotic spindle is a structure made of microtubules that plays a crucial role in separating chromosomes during mitosis.

Meiosis

Meiosis is a variation of cell division that produces gametes with half the number of chromosomes as the parent cell.
In humans, meiosis occurs in special cells in the ovaries or testes.
Fertilization fuses two gametes together, restoring the full chromosome number.

Interphase

Interphase is a much longer stage than mitosis, accounting for about 90% of the cell cycle.
Interphase can be divided into three phases: G1, S, and G2.
During interphase, the cell grows and produces proteins and cytoplasmic organelles.

Summary

The cell cycle is a tightly regulated process that ensures the accurate division of the genetic material during cell division.
Mitosis is a key process in growth, development, and repair.
Meiosis is responsible for producing gametes, the cells involved in sexual reproduction.
The cell cycle is essential for life and has many implications for human health.

Description

Explore the fascinating processes of cell division and the cell cycle. Understand the significance of mitosis and cytokinesis, and learn about the organization and function of chromosomes in eukaryotic cells. Discover how these biological processes contribute to reproduction, development, and cellular repair.