Cell Biology Overview

Definition: Study of the structure, function, and behavior of cells.
Cell Types:
- Prokaryotic Cells:
  - No nucleus or membrane-bound organelles.
  - DNA is circular and located in nucleoid region.
  - Examples: Bacteria and Archaea.
- Eukaryotic Cells:
  - Have a nucleus and membrane-bound organelles.
  - DNA is linear and associated with histones.
  - Examples: Plant and animal cells.
Cell Structure:
- Plasma Membrane:
  - Semi-permeable barrier controlling entry/exit of substances.
- Cytoplasm:
  - Gel-like substance where organelles are suspended.
- Organelles:
  - Mitochondria: Energy production (ATP synthesis).
  - Ribosomes: Protein synthesis.
  - Endoplasmic Reticulum:
    - Rough ER: Protein synthesis and folding.
    - Smooth ER: Lipid synthesis and detoxification.
  - Golgi Apparatus: Modifies, sorts, and packages proteins.
  - Lysosomes: Digestion of macromolecules.
  - Chloroplasts (in plants): Photosynthesis.
Cell Membrane Structure:
- Phospholipid bilayer with embedded proteins.
- Fluid mosaic model: Describes the dynamic nature of the membrane.

Purpose: To allow growth, development, and repair of tissues.
Types of Cell Division:
- Mitosis:
  - Produces two genetically identical daughter cells.
  - Involves one cell division.
  - Stages:
    1. Prophase: Chromatin condenses into chromosomes.
    2. Metaphase: Chromosomes align at the cell equator.
    3. Anaphase: Sister chromatids separate to opposite poles.
    4. Telophase: Nuclear membranes reform; chromosomes decondense.
    5. Cytokinesis: Division of cytoplasm.
- Meiosis:
  - Produces four genetically diverse daughter cells (gametes).
  - Involves two rounds of cell division (Meiosis I and II).
  - Key Features:
    - Reduction in chromosome number by half.
    - Genetic recombination through crossing over during Prophase I.
    - Stages:
      1. Meiosis I: Homologous chromosomes separate.
      2. Meiosis II: Sister chromatids separate.
Regulation of Cell Division:
- Cell cycle checkpoints: Ensure proper division and prevent errors.
- Cyclins and cyclin-dependent kinases (CDKs): Proteins that regulate the cell cycle.
Significance of Cell Division:
- Essential for growth, tissue repair, and reproduction (in the case of meiosis).
- Errors in cell division can lead to cancer and genetic disorders.

Study of cell structure, function, and behavior.
Cell Types:
- Prokaryotic Cells: Lack a nucleus and membrane-bound organelles; DNA is circular and found in nucleoid; examples include bacteria and archaea.
- Eukaryotic Cells: Possess a nucleus and membrane-bound organelles; DNA is linear and associates with histones; includes plant and animal cells.
Cell Structure:
- Plasma Membrane: Acts as a semi-permeable barrier regulating substance entry and exit.
- Cytoplasm: Gel-like substance housing organelles.
- Organelles:
  - Mitochondria: ATP synthesis, the powerhouse of the cell.
  - Ribosomes: Sites for protein synthesis.
  - Endoplasmic Reticulum (ER):
    - Rough ER: Involved in protein synthesis and folding.
    - Smooth ER: Responsible for lipid synthesis and detoxification processes.
  - Golgi Apparatus: Modifies, sorts, and packages proteins for secretion or use within the cell.
  - Lysosomes: Contain enzymes for digesting macromolecules.
  - Chloroplasts (in plants): Sites for photosynthesis.
Cell Membrane Structure:
- Composed of a phospholipid bilayer integrated with proteins; described by the fluid mosaic model representing its dynamic nature.

Purpose: Facilitates growth, development, and tissue repair.
Types of Cell Division:
- Mitosis: Results in two genetically identical daughter cells; single cell division.
  - Stages include:
    - Prophase: Chromatin condenses into distinct chromosomes.
    - Metaphase: Chromosomes align at the equatorial plate.
    - Anaphase: Sister chromatids are pulled apart to opposite ends.
    - Telophase: Nuclear membranes reform; chromosomes decondense.
    - Cytokinesis: Complete division of the cytoplasm.
- Meiosis: Produces four genetically diverse gametes; involves two rounds of division.
  - Key features:
    - Reduces chromosome number by half, essential for sexual reproduction.
    - Genetic recombination occurs via crossing-over in Prophase I.
    - Stages include:
      - Meiosis I: Homologous chromosomes separate.
      - Meiosis II: Sister chromatids segregate.
Regulation of Cell Division:
- Checkpoints in the cell cycle ensure accurate division and minimize errors.
- Cyclins and cyclin-dependent kinases (CDKs) are vital proteins that control progression through the cell cycle.
Significance of Cell Division:
- Critical for organismal growth, tissue repair, and sexual reproduction; errors can lead to cancer and genetic disorders.