Understanding the Cell Cycle, Mitosis, and Cancer Biology

The Cell Cycle

The cell cycle is a repetitive sequence of events that occurs from the time of a cell's formation until its division is completed.

Interphase

The control of cell division resides in the subphases of interphase. During this stage, the cell assembles the carbohydrates, lipids, and proteins needed for internal use and export. Subsequently, the DNA is copied, and protein synthesis drives the cell toward mitosis. Most of a cell's existence is spent in interphase.

Mitosis and Chromosome Number

All somatic cells of a particular species possess the same number of chromosomes.

Mitosis

• Prophase: Chromosomes become visible as rod-like units. Microtubules move one pair of centrioles to opposite poles of the cell, and the nuclear envelope begins to disintegrate. Microtubules of the spindle extend from the centrioles and attach to the centromeres of the duplicated chromosomes. The transition to metaphase occurs as the chromosomes begin an orderly arrangement.
• Anaphase: Chromosomes migrate to opposite poles. Once separated, each chromatid is considered an independent chromosome.
• Telophase: This stage begins when the chromosomes reach their respective poles.

Characteristics of Cancer Cells

Cancer cells exhibit several abnormal traits:

• They grow and divide uncontrollably.
• The cell membrane is leaky, and the cytoskeleton is disorganized.
• Cells have a weakened capacity for adhesion and may break away to migrate to other sites in the body.
• Cancer cells often have lethal effects on the organism.

Aerobic Respiration

• First Stage (Glycolysis): The breakdown of glucose into pyruvate; small amounts of ATP are generated.
• Second Stage (Krebs Cycle): Pyruvate is degraded into carbon dioxide and water. ATP is produced, and NAD and FAD accept H+ ions and electrons to be carried to the electron transfer chain.
• Third Stage (Electron Transfer Phosphorylation): Processes H+ ions and electrons to generate high yields of ATP, with oxygen acting as the final electron acceptor.

General Equation for Enzyme Activity

The Michaelis-Menten equation arises from the general equation for an enzymatic reaction: E + S ⇌ ES ⇌ E + P, where:

• E: Enzyme
• S: Substrate
• ES: Enzyme-substrate complex
• P: Product

The ES complex may dissolve back into the enzyme and substrate or move forward to form the final product.