Cell Cycle Overview

Cell Cycle

• The cell cycle describes how eukaryotic cells divide.
• Eukaryotes have a nucleus containing multiple linear chromosomes, while prokaryotes have a single looped chromosome outside of a nucleus.
• Humans have 46 chromosomes in most cells, with half coming from each parent.
• The cell cycle is divided into two main phases: interphase and mitosis.

Interphase

• Interphase is the longest phase of the cell cycle, when the cell grows and prepares for division.
• Interphase consists of three subphases: G1, S, and G2.
• G1 (Gap 1) is the initial growth phase where organelles are produced.
• S (Synthesis) is the phase where DNA replicates, doubling the number of chromosomes.
• G2 (Gap 2) is the phase where errors in the newly synthesized DNA are repaired.

Mitosis

• Mitosis is the division of the nucleus, ensuring each daughter cell receives a complete set of chromosomes.
• Mitosis begins with a diploid (2N) number of chromosomes and ends with two identical diploid cells.
• Mitosis is not the entire cell cycle, it's just a part of it.
• Mitosis involves four main phases: prophase, metaphase, anaphase, and telophase.
• Prophase: Chromosomes condense and move towards the center of the cell.
• Metaphase: The chromosomes align randomly along the middle of the cell, and spindle fibers form.
• Anaphase: Spindle fibers attach to the centromere of the chromosomes, pulling them apart to opposite sides of the cell.
• Telophase: The cell begins to pinch in, the nucleus reforms, and in plant cells, a cell plate forms to separate the daughter cells.

Terms & Definitions

• Cytokinesis: The division of the cytoplasm following nuclear division.
• Homologous Chromosomes: Identical chromosomes, one from each parent, with the same size and genes.
• Centromere: The central part of a chromosome where sister chromatids are joined.
• Sister Chromatids: The original chromosome and its copy made during the S phase of interphase.

Meiosis

• Meiosis is a type of cell division that produces four haploid (N) daughter cells from a diploid (2N) parent cell.
• It involves two rounds of division, resulting in gametes (sex cells).
• Prophase I is unique to meiosis and involves crossing over, which creates genetic diversity.
• The random alignment of chromosomes during meiosis also contributes to genetic diversity.

Stem Cells

• Stem cells are undifferentiated cells that can develop into various cell types.
• Embryonic stem cells are more responsive to programming than adult stem cells.
• Stem cell research is controversial because some people believe it involves aborted fetal tissue, however, this is not true.

Cancer

• Uncontrolled cell division can lead to cancer.
• Tumors are abnormal growths of cells.
• Malignant tumors are cancerous and can metastasize (spread to other tissues).
• Benign tumors are not cancerous and do not spread.