Cell Biology: The Cell Cycle and Division

Study Notes

Organisms reproduce to ensure species survival through cell division.
Cell division enables the production of offspring and the replacement of damaged cells.
Two types of cell division: mitosis (somatic cells) and meiosis (gametes).

The cell cycle consists of distinct phases of growth, DNA replication, and division.
Divided into two main stages:
- Interphase: non-dividing (G1, S, G2 phases, G0)
- Cell Division: mitosis for somatic cells and meiosis for gametes.

Interphase is the growth phase where cells replicate genetic material and organelles.
Some cells enter the G0 phase, where they are unlikely to divide but continue normal functions.

Highly differentiated cells like neurons and heart muscle cells are often permanently in G0.
Lymphocytes can remain in G0 for years until needed for immune response.

Checkpoints regulate cell cycle progression to prevent mutations and ensure correct timing.
Cells assess internal conditions at checkpoints to decide on phase progression.

Cancer is characterized by uncontrolled abnormal cell division and can result from cell cycle disruptions.
Tumors can be benign (non-invasive) or malignant (can metastasize).
Causes of cancer include:
- Lifestyle factors (e.g., smoking, high-fat diet).
- Genetic factors (family history).
- Environmental exposures (viruses, carcinogens).

Chemotherapy: uses drugs to kill actively dividing cells, administered systemically.
Surgery: involves the removal of cancerous tissue.
Radiation therapy: uses X-rays to kill cancer cells and shrink tumors.

Chromosome abnormalities can cause serious health issues due to errors in cell division.
Karyotyping: a technique to analyze chromosomes for abnormalities.

Aneuploidy: abnormal number of chromosomes.
- Down Syndrome (Trisomy 21): third copy of chromosome 21; physical traits include short neck and slanted eyes.
- Turner Syndrome (45, XO): missing or abnormal X chromosome; affects females and may include short stature and webbed neck.
- Klinefelter Syndrome (47, XXY): extra X chromosome in males; leads to infertility and physical differences.
- Trisomy X Syndrome (47, XXX): extra X chromosome in females; mild symptoms, often taller than average.
- Patau Syndrome (Trisomy 13): extra chromosome 13; physical traits include cleft lip and polydactyly.
- Edward Syndrome (Trisomy 18): extra chromosome 18; characterized by developmental delays and various physical defects.

Altered chromosome structures lead to genetic conditions.
- Deletion: missing segment of a chromosome.
- Duplication: repeated segment of a chromosome.
- Translocation: transfer of a chromosome segment to a non-homologous chromosome.
- Inversion: rotation of a chromosome segment by 180 degrees.