Cell Cycle, Mitosis, and Cancer: Study Guide

Cell Cycle, Mitosis, and Cancer

Key Cell Cycle Terms

The cell cycle is a series of events that cells go through as they grow and divide. Understanding the terminology is essential for mastering cell division and its regulation.

• Chromatin: Loosely packed DNA and proteins in interphase; not visible as distinct structures.

• Chromosome: Condensed, distinct forms of DNA visible during mitosis.

• Chromatid: One of two identical strands of a duplicated chromosome.

• Sister Chromatids: The two identical chromatids joined at a centromere.

• Centromere: Region where sister chromatids are joined; spindle fibers attach here during mitosis.

• Spindle Fibers / Microtubules: Structures that pull chromosomes apart during mitosis.

• Nuclear Membrane: Membrane that encloses the nucleus; breaks down in prophase and reforms in telophase.

Interphase – "Cell Grows and Prepares"

Interphase is the phase of the cell cycle where the cell grows, replicates its DNA, and prepares for division. It consists of three subphases: G1 (cell grows), S (DNA synthesis/replication), and G2 (preparation for mitosis).

• G1 Phase: Cell grows, increases organelles.

• S Phase: DNA replicates; chromosomes duplicate.

• G2 Phase: Cell prepares for mitosis; checks for DNA errors.

Chromatin is present throughout interphase, and chromosomes are not yet visible as distinct structures.

Mitosis – "Cell Divides"

Mitosis is the process by which a eukaryotic cell separates its duplicated chromosomes into two identical sets, resulting in two daughter cells. It is divided into several stages:

Stage	What Happens	Chromosome Form / Key Features
Prophase	Chromosomes condense; spindle fibers form; nuclear membrane dissolves	Chromosomes condensed
Metaphase	Chromosomes align at metaphase plate; spindle fibers attach to centromeres	Duplicated chromosomes visible in X-shaped structures
Anaphase	Sister chromatids separate to move to opposite poles	Chromatids move (now called chromosomes)
Telophase	Chromosomes decondense; nuclear membrane reforms	Each set has full set of chromosomes
Cytokinesis	Cytoplasm divides; 2 daughter cells form	Each cell has full set of DNA

Mnemonic: PMAT = Prophase, Metaphase, Anaphase, Telophase

Cancer

Cancer is a disease characterized by uncontrolled cell division. Cancer cells have several distinct properties:

• Unregulated cell cycle

• Loss of contact inhibition (cells grow over each other)

• Can invade other tissues (metastasis)

• Fail to undergo normal cell death (apoptosis)

• May form tumors (masses of abnormal cells)

Example: Mutations in genes like p53 can prevent damaged cells from stopping division, leading to cancer.

Mitotic Index

The mitotic index is a measure of the percentage of cells undergoing mitosis in a given cell population. It is used to estimate cell proliferation rates, especially in cancer studies.

• Formula:

$\text{Mitotic Index (\%)} = \frac{\text{Cells in mitosis}}{\text{Total cells observed}} \times 100$

• Example: If 5 cells are in mitosis out of 23 total cells:

$\frac{5}{23} \times 100 = 21.7\%$

Study Tips

• Draw or label chromatin → chromosome → chromatid transitions.

• Visualize spindle fibers and centromeres in metaphase/anaphase.

• Remember: Interphase = chromatin, Mitosis = chromosomes, Telophase = chromatin again.

• Practice PMAT + Cytokinesis order and mitosis role in asexual reproduction.

• Relate cancer concepts to checkpoints: p53 stops damaged cells; mutation = uncontrolled division.