Chapter 10 pt.1 (March 17, 2024)

Overview of Mitosis

• Mitosis is one of the two types of cell division, the other being meiosis.

• It is part of the cell theory that states all cells come from pre-existing cells.

• Mitosis produces two genetically identical daughter cells, often referred to as clones.

Types of Cell Division

Prokaryotic Division

• Prokaryotes undergo cell division through a process called binary fission.

Eukaryotic Division

• Eukaryotic cells (including multicellular organisms) undergo mitosis for growth, repair, and maintenance.

• Mitosis is essential for a multicellular organism to develop from a single fertilized egg into a complete organism.

Mechanisms of Division

Asexual Reproduction

• In unicellular organisms, like amoebae, mitosis is a form of asexual reproduction, generating new cells without the need for a mate.

• This allows rapid population increase in stable environments, as genetic clones are produced.

Sexual Reproduction

• Sexual reproduction involves meiosis which leads to gametes (sperm and egg cells) and introduces genetic diversity.

• Genetic variation is crucial for adaptation to changing environments.

Stages of the Cell Cycle

Interphase

• Most of a cell's life is spent in interphase, which includes three sub-phases:

  • G1 (Growth Phase 1): The cell grows, functions and prepares for DNA replication.

  • S (Synthesis Phase): DNA is replicated, forming sister chromatids for each chromosome.

  • G2 (Growth Phase 2): The cell prepares for mitosis, ensuring all organelles and DNA are in order.

M Phase (Mitosis and Cytokinesis)

• Mitosis: The actual process of nuclear division, which is divided into several stages:

  1. Prophase: Chromatin condenses into visible chromosomes; the nuclear envelope begins to break down.

  2. Prometaphase: Nuclear envelope completely disintegrates; spindle fibers attach to kinetochores on chromosomes.

  3. Metaphase: Chromosomes align at the cell equator; spindle checkpoint ensures proper attachment.

  4. Anaphase: Sister chromatids are pulled apart to opposite poles of the cell.

  5. Telophase: Nuclear envelopes re-form around separated sets of chromosomes; chromosomes decondense.

• Cytokinesis: The physical division of the cytoplasm into two daughter cells, differing in mechanisms for plant and animal cells:

  • Animal Cells: Involve the formation of a cleavage furrow powered by actin and myosin.

  • Plant Cells: Involve the formation of a cell plate to create a new cell wall.

Checkpoints in Cell Cycle Regulation

• The cell cycle is regulated by a series of checkpoints that assess cell conditions and prevent errors before proceeding to the next phase.

• Critical for maintaining genomic stability and preventing cancer.

Chromatin vs. Chromosomes

• Chromatin: Uncondensed DNA found in non-dividing cells, which is less organized, allowing access for replication and gene expression.

• Chromosomes: Condensed DNA structures visible during cell division, facilitating separation during mitosis.

• Each chromosome consists of two identical sister chromatids after DNA replication.

Terminology

• Diploid Cells (2n): Cells containing two sets of homologous chromosomes (46 in humans).

• Haploid Cells (n): Cells containing one set of chromosomes (23 in humans).

• Sister Chromatids: Identical copies of each chromosome, connected at the centromere.

• Homologous Chromosomes: Chromosomes that have the same sequence of genes but may have different alleles.

Importance of Mitosis

• Mitosis is essential for growth, tissue repair, and asexual reproduction in organisms.

• Understanding mitosis is critical for cancer research, as uncontrolled cell division is a hallmark of cancer.