Chapter 9: The Cell Cycle – Study Notes

Chapter 9: The Cell Cycle

Overview of the Cell Cycle

The cell cycle is the series of events that cells go through as they grow and divide. It ensures that genetic material is accurately replicated and distributed to daughter cells. The cell cycle is fundamental to growth, development, and tissue repair in multicellular organisms.

• Key Phases: Interphase (G1, S, G2) and Mitotic Phase (Mitosis and Cytokinesis)

• Purpose: To produce genetically identical daughter cells for growth and repair

Key Concepts

• 9.1: Mitosis and cell division result in genetically identical daughter cells

• 9.2: The mitotic phase alternates with interphase in the cell cycle

• 9.3: The eukaryotic cell cycle is regulated by a molecular control system

Major Stages of the Cell Cycle

Interphase

Interphase is the longest phase of the cell cycle, during which the cell grows, replicates its DNA, and prepares for division.

• G1 phase: Cell growth and normal functions

• S phase: DNA replication

• G2 phase: Preparation for mitosis

Mitotic Phase (M Phase)

The mitotic phase includes mitosis (division of the nucleus) and cytokinesis (division of the cytoplasm).

• Mitosis: Division of the cell's nucleus into two genetically identical nuclei

• Cytokinesis: Division of the cytoplasm, resulting in two daughter cells

Key Terms and Structures

• Chromatin: The complex of DNA and proteins that makes up chromosomes in eukaryotic cells

• Chromosome: A structure consisting of DNA and associated proteins, visible during cell division

• Chromatid: Each of the two identical halves of a duplicated chromosome

• Centromere: The region where two sister chromatids are joined and where spindle fibers attach during mitosis

• Genome: The complete set of genetic material in an organism

• Somatic Cell: Any cell in the body except gametes (sperm and egg)

• Gamete: A reproductive cell (sperm or egg) that contains half the number of chromosomes of a somatic cell

Functions of Cell Division

Function	Example
Growth	Increase in size of multicellular organisms
Repair	Healing of wounds by replacing damaged cells
Reproduction	Asexual reproduction in unicellular organisms

Chromosome Structure and Terminology

• Chromatid: One of two identical "sister" parts of a duplicated chromosome

• Centromere: The constricted region joining the two sister chromatids

• Chromatin: DNA-protein complex in the nucleus; condenses to form chromosomes during cell division

Phases of Mitosis

Phase	Important Features of Phase
Prophase	Chromosomes condense, spindle apparatus begins to form
Prometaphase	Nuclear envelope breaks down, spindle fibers attach to kinetochores
Metaphase	Chromosomes align at the metaphase plate
Anaphase	Sister chromatids separate and move toward opposite poles
Telophase	Nuclear envelopes reform, chromosomes decondense

Cytokinesis

• Animal Cells: Cytokinesis occurs by cleavage, forming a cleavage furrow that pinches the cell in two

• Plant Cells: Cytokinesis occurs by formation of a cell plate, which develops into a new cell wall

Control of the Cell Cycle

• Checkpoints: Control points where stop and go-ahead signals regulate the cycle

• Major Checkpoints: G1, G2, and M

• Regulatory Proteins: Cyclins and cyclin-dependent kinases (Cdks) control progression through the cycle

Checkpoint	What Happens? How Is It Controlled?
G1	Cell commits to division; controlled by growth factors and cell size
G2	Checks for DNA damage and completion of replication
M	Ensures all chromosomes are attached to spindle before anaphase

Mitotic Spindle and Chromosome Movement

• Mitotic Spindle: Structure made of microtubules that separates chromosomes during mitosis

• Centrosome: Microtubule-organizing center; duplicates during interphase

• Kinetochores: Protein complexes on centromeres where spindle fibers attach

Binary Fission in Prokaryotes

Prokaryotes reproduce by binary fission, a form of asexual reproduction where the cell divides into two genetically identical cells.

• Steps: DNA replication, chromosome segregation, cytokinesis

Regulation and Cancer

• Density-dependent inhibition: Normal cells stop dividing when crowded; cancer cells do not

• Anchorage dependence: Normal cells must be attached to a substrate to divide; cancer cells may not require this

• Transformation: Process by which a normal cell becomes a cancer cell

• Benign vs. Malignant Tumors: Benign tumors do not spread; malignant tumors invade tissues and can metastasize

• Metastasis: Spread of cancer cells to distant parts of the body

Cancer Treatments

• Surgery: Removal of tumors

• Chemotherapy: Use of drugs to kill dividing cells

• Radiation Therapy: Use of high-energy radiation to destroy cancer cells

Summary Table: Cell Cycle Checkpoints

Checkpoint	What Happens? How Is It Controlled?
G1	Cell commits to division; controlled by growth factors and cell size
G2	Checks for DNA damage and completion of replication
M	Ensures all chromosomes are attached to spindle before anaphase

Key Equations and Concepts

• Number of Chromosomes in Humans: 46 in somatic cells, 23 in gametes

• DNA Replication: Occurs during S phase of interphase

Example:

• In humans, each somatic cell contains 46 chromosomes (23 pairs). After DNA replication, each chromosome consists of two sister chromatids joined at the centromere.

Additional info: The above notes expand on the provided questions by supplying definitions, explanations, and context for each major topic in the cell cycle, as would be expected in a mini-textbook summary for General Biology students.