The Cell Cycle and Mitosis: Study Guide for Anatomy & Physiology

The Cell Cycle

Major Periods of the Cell Cycle

The cell cycle is the series of events that cells go through as they grow and divide. It consists of two major periods: Interphase and the Mitotic (M) phase.

• Interphase: The period of cell growth and DNA replication. The cell prepares for division during this phase.

• Mitotic (M) Phase: The period during which the cell divides its nucleus and cytoplasm to produce two daughter cells.

Subphases of Interphase

Interphase is subdivided into three distinct subphases, each with specific cellular activities:

• G1 Phase (First Gap): The cell grows, produces organelles, and synthesizes proteins necessary for DNA replication.

• S Phase (Synthesis): DNA replication occurs, resulting in two identical sets of chromosomes.

• G2 Phase (Second Gap): The cell continues to grow and prepares for mitosis by producing microtubules and other components.

The Mitotic Phase

Events of the Mitotic Phase

The mitotic phase consists of two distinct events:

• Mitosis: Division of the nucleus, resulting in two genetically identical nuclei.

• Cytokinesis: Division of the cytoplasm, producing two separate daughter cells.

Phases of Mitosis

Mitosis is divided into several phases, each characterized by specific changes in the cell:

• Prophase: Chromatin condenses into visible chromosomes; spindle fibers begin to form; nuclear envelope breaks down.

• Metaphase: Chromosomes align at the cell's equatorial plane (metaphase plate); spindle fibers attach to centromeres.

• Anaphase: Sister chromatids are pulled apart toward opposite poles of the cell.

• Telophase: Chromosomes decondense; nuclear envelopes reform around each set of chromosomes.

Structures Involved in Mitosis

Key Components and Their Roles

• Aster(s): Star-shaped structures formed around centrosomes; help organize spindle fibers during cell division.

• Cell Plate (Plant Cells): Structure that forms during cytokinesis in plant cells, leading to the separation of daughter cells.

• Chromatid(s): Each of the two identical halves of a duplicated chromosome.

• Chromosome(s): Structures composed of DNA and proteins; carry genetic information.

• Cleavage Furrow (Animal Cells): Indentation that forms during cytokinesis in animal cells, eventually splitting the cell in two.

• Spindle Fiber(s): Microtubules that attach to chromosomes and help separate them during mitosis.

Microscopic Identification of Mitotic Phases

Recognizing Phases in Animal and Plant Cells

Using microscopes or models, students should be able to identify the different phases of mitosis in both animal and plant cells by observing the arrangement and appearance of chromosomes and cell structures.

• Animal Cells: Look for the presence of a cleavage furrow during cytokinesis.

• Plant Cells: Look for the formation of a cell plate during cytokinesis.

Cytokinesis: Animal vs. Plant Cells

Differences in Cytokinesis

Cytokinesis differs between animal and plant cells due to structural differences:

• Animal Cells: Cytokinesis occurs via the formation of a cleavage furrow, which pinches the cell into two.

• Plant Cells: Cytokinesis occurs via the formation of a cell plate, which develops into a new cell wall separating the two daughter cells.

Comparison Table: Cytokinesis in Animal vs. Plant Cells

Feature	Animal Cells	Plant Cells
Mechanism	Cleavage furrow formation	Cell plate formation
Structure Involved	Actin microfilaments	Vesicles from Golgi apparatus
Result	Two separate daughter cells	New cell wall between daughter cells

Key Terms and Definitions

• Cell Cycle: The ordered sequence of events that leads to cell division and duplication.

• Mitosis: The process of nuclear division in eukaryotic cells that results in two identical daughter nuclei.

• Cytokinesis: The division of the cytoplasm to form two separate daughter cells.

• Chromosome: A thread-like structure of nucleic acids and protein found in the nucleus, carrying genetic information.

• Chromatid: One of two identical halves of a replicated chromosome.

• Spindle Fiber: Microtubules that separate chromosomes during mitosis.

Relevant Equations

While the cell cycle does not involve complex mathematical equations, the following formula is sometimes used to estimate the duration of a cell cycle phase:

• Relative Duration of Phase:

$\text{Relative Duration} = \frac{\text{Number of cells in phase}}{\text{Total number of cells observed}}$

Example Application

If 20 out of 100 observed cells are in metaphase, the relative duration of metaphase is:

$\text{Relative Duration} = \frac{20}{100} = 0.2$

This means 20% of the cell cycle is spent in metaphase (in this sample).