JCU Mitosis and Meiosis Study Notes

JCU Mitosis and Meiosis Study Notes

Overview

This study guide encompasses detailed notes on the processes of mitosis and meiosis, fundamental concepts of the cell cycle, definitions, stages, and differences between the two types of cell division.

Learning Outcomes

• Understand how chromosomes are organized.

• Identify the stages of the eukaryotic cell cycle, their individual function, and how these processes are controlled.

• Distinguish between mitosis and meiosis by identifying their differences and similarities.

• Explain the contexts of mitosis occurrence, including when, where, why, and the processes involved.

• Describe the significance of meiosis and outline its stages.

• Differentiate between haploid, diploid, and define homologous chromosomes.

Cellular Fundamentals

Definition of Cells

• Cells are the basic units of life, and every living organism is composed of cells, which constitute all parts of the human body, such as skin, hair, nails, and blood.

Genetic Material

• Cells contain hereditary material known as the genome, which is the complete set of genes or genetic material present in a cell or organism.

• The genome is composed of DNA (deoxyribonucleic acid).

Types of Cells

• There are two archetypes of cells:

  1. Prokaryotes - cells without a nucleus (e.g., bacteria).

  2. Eukaryotes - cells with a nucleus (e.g., plant and animal cells).

What is DNA?

• DNA is described as the hereditary material in organisms, containing the instructions needed to develop and direct the activities of nearly all living organisms.

• Most DNA is housed in the cell nucleus, consisting of two twisting, paired strands known as a double helix.

  • DNA is intricately structured along with proteins to form packaging units such as chromosomes.

Chromosome Structure

• Chromosomes consist of a complex of DNA and protein known as chromatin, composed of:

  • 40% DNA

  • 60% protein

• In eukaryotes, the number of chromosomes in somatic cells ranges from 10 to 50; humans specifically have 46 chromosomes organized into 23 pairs known as karyotypes.

The Eukaryotic Cell Cycle

Cell Cycle Phases

1. Interphase - The phase where the cell prepares for division. It includes:

   • G1 phase (first gap): Cell growth, organelle replication, and normal metabolism.

   • S phase (synthesis): DNA replication where chromosomes duplicate.

   • G2 phase (second gap): Preparing for mitosis, including DNA packaging and protein synthesis.

2. M Phase (Mitotic Phase) - Mitosis occurs, consisting of the stages: Prophase, Metaphase, Anaphase, Telophase, and Cytokinesis.

Duration of the Cell Cycle

• The eukaryotic cell cycle duration varies from 8 to 20 hours in animal cells.

Stages of Mitosis

Mitosis is the process creating two identical diploid daughter cells, occurring in all body cells except reproductive cells:

1. Prophase: Chromosomes condense and become visible; the nuclear envelope breaks down, and spindle fibers form.

2. Metaphase: Chromosomes align at the cell's equator; spindle fibers attach to kinetochores.

3. Anaphase: Sister chromatids are separated and pulled towards opposite poles.

4. Telophase: Chromosomes arrive at the poles, de-condense, and the nuclear envelope re-forms.

5. Cytokinesis: Division of the cytoplasm into two daughter cells, differing mechanisms occur in animal (cleavage furrow) and plant cells (cell plate).

Key Points about Mitosis

• Mitosis does not change chromosome number, resulting in diploid cells identical to the parent cell.

• Crucial for growth, development, and tissue repair.

What is Meiosis?

• Meiosis is the specialized process by which one diploid cell (2n) divides to produce four haploid cells (n), which are gametes (i.e., eggs and sperm).

• Meiosis occurs in all sexually reproducing organisms, leading to genetic diversity through processes like crossing over and independent assortment.

Meiosis vs. Mitosis

• Differences: Mitosis results in two identical daughter cells, while meiosis results in four genetically diverse daughter cells.

• Crossing Over: In prophase I of meiosis, crossing over occurs, allowing genetic material exchange between homologous chromosomes, increasing genetic variability.

• Independent Assortment: During anaphase I, homologous chromosomes are distributed randomly into the daughter cells.

Stages of Meiosis

Meiosis I

1. Prophase I: Chromosomes condense, and crossing over occurs.

2. Metaphase I: Homologous chromosomes align at the equator.

3. Anaphase I: Homologous chromosomes are pulled apart to opposite poles.

4. Telophase I and Cytokinesis: Cells divide into two diploid cells.

Meiosis II

1. Prophase II: Chromosomes condense again in both daughter cells.

2. Metaphase II: Chromosomes line up at the equator of each haploid cell.

3. Anaphase II: Sister chromatids separate and move towards opposite poles.

4. Telophase II and Cytokinesis: Cells divide to produce four haploid cells.

Outcome of Meiosis

• The genetic variation resulting from meiosis is critical for evolution and biodiversity, crucial for adaptation in populations.

Summary of Mitosis vs. Meiosis