🐇Honors Biology Unit 6 – Cell Division – Mitosis and Meiosis

Key Concepts and Terminology

• Cell division process of cells reproducing to create new cells
• Mitosis division of somatic cells resulting in two genetically identical daughter cells
• Meiosis division of germ cells resulting in four genetically diverse haploid cells (gametes)
• Interphase stage between cell divisions when the cell grows and prepares for division
  • G1 phase cell grows and carries out normal functions
  • S phase DNA replication occurs
  • G2 phase cell prepares for division
• Cytokinesis physical division of the cytoplasm to form two separate daughter cells
• Chromosomes structures containing genetic material (DNA) that condense during cell division
• Centromere region of the chromosome where sister chromatids are attached
• Spindle fibers protein structures that attach to chromosomes and pull them apart during division

The Cell Cycle Overview

• Cell cycle series of events that take place in a cell leading to its division and replication
• Consists of two main phases: interphase and mitotic phase (M phase)
• Interphase longest phase of the cell cycle, divided into three sub-phases (G1, S, and G2)
  • During G1, the cell grows and carries out normal functions
  • In S phase, DNA replication occurs, doubling the genetic material
  • G2 phase involves preparation for cell division
• M phase relatively short, consists of mitosis and cytokinesis
• Mitosis divided into four stages (prophase, metaphase, anaphase, and telophase)
• Cytokinesis occurs concurrently with telophase, physically dividing the cytoplasm
• Cell cycle regulated by various checkpoints and control mechanisms to ensure proper division

Mitosis: Stages and Process

• Mitosis division of somatic cells, resulting in two genetically identical daughter cells
• Consists of four main stages: prophase, metaphase, anaphase, and telophase
• Prophase chromosomes condense, nuclear envelope breaks down, and spindle fibers form
  • Centrioles move to opposite poles of the cell
• Metaphase chromosomes align at the equatorial plane of the cell
  • Spindle fibers attach to the centromeres of the chromosomes
• Anaphase sister chromatids separate and move towards opposite poles of the cell
  • Spindle fibers shorten, pulling the chromatids apart
• Telophase chromosomes decondense, nuclear envelopes reform, and spindle fibers disassemble
• Cytokinesis occurs concurrently with telophase, dividing the cytoplasm and forming two daughter cells
• Mitosis maintains the genetic stability of an organism by producing identical daughter cells

Meiosis: Stages and Process

• Meiosis division of germ cells, resulting in four genetically diverse haploid cells (gametes)
• Consists of two divisions: meiosis I and meiosis II
• Meiosis I reduction division, halving the number of chromosomes
  • Prophase I chromosomes condense, homologous chromosomes pair up and form synapsis
  • Metaphase I homologous pairs align at the equatorial plane
  • Anaphase I homologous chromosomes separate and move to opposite poles
  • Telophase I two haploid daughter cells form, each with half the number of chromosomes
• Meiosis II similar to mitosis, resulting in four haploid daughter cells
  • Prophase II chromosomes condense, and spindle fibers form
  • Metaphase II chromosomes align at the equatorial plane
  • Anaphase II sister chromatids separate and move to opposite poles
  • Telophase II four haploid daughter cells (gametes) form
• Crossing over and independent assortment during meiosis I introduce genetic variation

Comparing Mitosis and Meiosis

• Mitosis and meiosis are both forms of cell division but serve different purposes
• Mitosis occurs in somatic cells, while meiosis occurs in germ cells
• Mitosis results in two genetically identical daughter cells, while meiosis produces four genetically diverse haploid cells
• Mitosis involves one division, while meiosis consists of two divisions (meiosis I and II)
• Mitosis maintains the genetic stability of an organism, while meiosis introduces genetic variation through crossing over and independent assortment
• The daughter cells produced by mitosis are diploid, while those produced by meiosis are haploid
• Mitosis is essential for growth, repair, and regeneration, while meiosis is crucial for sexual reproduction and genetic diversity

Cellular Regulation and Control

• Cell cycle regulated by various checkpoints and control mechanisms
• Checkpoints ensure that the cell has completed all necessary steps before proceeding to the next phase
  • G1 checkpoint ensures the cell is ready for DNA replication
  • G2 checkpoint ensures DNA replication is complete and the cell is ready for mitosis
  • M checkpoint (spindle checkpoint) ensures proper attachment of chromosomes to spindle fibers
• Cyclins and cyclin-dependent kinases (CDKs) are key regulators of the cell cycle
  • Cyclins bind to and activate CDKs, which phosphorylate target proteins to initiate specific events
• Tumor suppressor genes (e.g., p53) and proto-oncogenes (e.g., Ras) play crucial roles in regulating cell division
  • Mutations in these genes can lead to uncontrolled cell growth and cancer
• Apoptosis (programmed cell death) is another important regulatory mechanism that eliminates damaged or unwanted cells

Real-World Applications

• Understanding cell division is crucial for many real-world applications
• Cancer research heavily relies on knowledge of cell division, as cancer is characterized by uncontrolled cell growth and division
  • Targeted therapies aim to inhibit specific pathways or proteins involved in cell division to halt tumor growth
• Regenerative medicine and tissue engineering utilize the principles of cell division to develop treatments for injuries and diseases
  • Stem cells, which can divide and differentiate into various cell types, are a key focus in this field
• Agricultural biotechnology employs knowledge of cell division to develop improved crop varieties (disease-resistant, higher-yielding)
• Forensic science uses the understanding of cell division and DNA replication in techniques such as DNA fingerprinting and paternity testing

Common Misconceptions and FAQs

• Misconception: Mitosis and meiosis are the same processes
  • Fact: While both are forms of cell division, they serve different purposes and produce different outcomes
• Misconception: Cells divide continuously without any regulation
  • Fact: The cell cycle is tightly regulated by checkpoints and control mechanisms to ensure proper division
• FAQ: What happens if cell division goes wrong?
  • Uncontrolled cell division can lead to the formation of tumors and cancer
  • Errors in meiosis can result in chromosomal abnormalities and genetic disorders (Down syndrome)
• FAQ: Are the daughter cells produced by mitosis always identical?
  • While mitosis aims to produce genetically identical daughter cells, mutations can occur during DNA replication, leading to slight variations
• FAQ: Why is meiosis important for sexual reproduction?
  • Meiosis produces haploid gametes, which allows for the restoration of the diploid number upon fertilization and introduces genetic variation in offspring