Use a model of the cell cycle to explain how mitosis produces identical cells for growth and repair, and how a loss of cycle control leads to cancer (Tennessee Academic Standards for Science, Biology I, BIO1.LS1).

What this topic is asking

The Tennessee LS1 standards (growth and development of organisms) ask you to model how cells grow and divide. For the Biology I EOC that means knowing the stages of the cell cycle, what mitosis produces and why, and the cause-and-effect chain from a mutation in cell-cycle genes to cancer. Items often show a diagram of cells at different phases or a short scenario about uncontrolled growth, so understanding the cycle as a regulated sequence is the goal.

The cell cycle: interphase plus division

Interphase is itself divided into three parts: G1 (growth), S (DNA synthesis, when the chromosomes are copied), and G2 (more growth and preparation to divide). A common EOC misconception is that the cell spends most of its time dividing; in fact it spends most of its time in interphase, especially copying its DNA in the S phase.

Mitosis: PMAT

After interphase, the nucleus divides by mitosis in four phases, remembered as PMAT:

• Prophase. The copied chromosomes condense into visible structures (each is two identical sister chromatids joined at a centromere), and the nuclear envelope breaks down.
• Metaphase. The chromosomes line up along the middle (the metaphase plate) of the cell.
• Anaphase. The sister chromatids separate and are pulled to opposite ends of the cell.
• Telophase. A new nuclear envelope forms around each set of chromosomes, producing two nuclei.

Mitosis is then followed by cytokinesis, the division of the cytoplasm into two separate cells. EOC ordering items may ask you to place these phases in sequence, so the PMAT acronym is worth memorizing.

What mitosis produces, and why it matters

This is the central contrast with meiosis, which halves the chromosome number and shuffles the genes to make variable gametes for sexual reproduction (see meiosis and genetic variation). On the EOC, "identical, same number, for growth and repair" means mitosis; "different, half the number, for reproduction" means meiosis.

Control, checkpoints, and cancer

The cell cycle does not run freely; it is regulated by genes that act as checkpoints, telling a cell when it is safe to proceed and when to stop, repair damage, or self-destruct. This regulation is the link to disease.

A mutation in those regulatory genes can disable the controls. When the checkpoints fail, the cell may divide in an uncontrolled way. The result is an abnormal mass of cells called a tumor. A tumor that stays in place is benign; a malignant tumor that invades nearby tissue or spreads through the body is cancer. The cause-and-effect chain the EOC tests is: mutation in cell-cycle genes, then loss of control, then uncontrolled division, then tumor, then cancer.

Try this

Q1. List the four phases of mitosis in order. [2]

• Cue. Prophase, metaphase, anaphase, telophase (PMAT).

Q2. A cell spends most of the cell cycle in one stage. Name it and state two things that happen during it. [2]

• Cue. Interphase; the cell grows, carries out its normal functions, and replicates (copies) its DNA.