The Cell Cycle 3.2.2

Name and describe the 1st stage of the cell cycle

During interphase, the cell caries out its normal function, it has 3 sections: G1, S and G2.
G1 involves cell growth. S involves DNA replication. G2 involves preparation for mitosis - e.g. development of spindle fibres.

Name and describe the 2nd stage of the cell cycle? (briefly)

Mitosis is the division of the nucleus in eukaryotic cells dividing to produce two genetically identical nuclei. Mitosis includes Prophase, Metaphase, Anaphase and Telophase.

Why is mitosis important?

Growth: all cells produced in mitosis are identical so can be used for growth.
Repair: daughter cells produced can replace dying tissue.
Reproduction: some single-celled organisms asexually reproduce using mitosis.
Production of stem cells: stem cells divide by mitosis.

Prophase

Chromosomes condense. Centrioles migrate to opposite poles of the cell and begin forming spindle fibres. The nuclear envelope starts to break down, and the nucleolus disappears, leaving the chromosomes free in the cytoplasm.

Metaphase

The chromosomes line up along the equator of the cell, and spindle fibres (called microtubules) attach to the centromere of each chromosome.

Anaphase

The centromeres divide and the chromatids are separated and pulled to opposite poles of the cell by spindle fibres.

Telophase

When chromatids reach poles of cell, they uncoil and become long thin chromosomes again. A nuclear envelope forms around each set of chromosomes to form two nuclei, and nucleolus reforms.

What is the 3rd stage of the cell cycle?

Cytokinesis- after mitosis, the cytoplasm and cell membrane divides, producing two genetically identical daughter cells.

What is a homologous pair?

A pair of chromosomes, one is paternal and one is maternal. These chromosomes have identical genes but may contain different alleles. They are separated during mitosis.

Diploid vs haploid cells

Diploid cells contain two copies of each chromosome. 2n. Body cells.

Haploid cells contain one copy of each chromosome. n. Reproductive cells.

Cancer

Mutations in the genes that control mitosis can lead to uncontrolled cell division and growth, resulting in the formation of a tumour. Some cancer-treating drugs target S phase (prevent the DNA from replicating) and some target metaphase (prevent the formation of spindle fibres).

Prokaryotic replication

Binary fission.
The cell grows and circular chromosomes are replicated once and plasmids are replicated many times. The circular chromosomes move to opposite poles of the cell. The cell membrane begins to divide and new cell walls form between the two DNA molecules. The cytoplasm divides and two identical (except plasmids) daughter cells are formed.