PHYSICAL BASIS OF HEREDITY

• The invention of the compound light microscope by Zacharias Jansen allowed for the early exploration of cells
• In 1665, Robert Hooke observed plant cells in cork slices and coined the term "cell"
• Anton van Leeuwenhoek's discoveries in 1673 included blood cells, sperm cells, and microorganisms
• Robert Brown discovered the cell nucleus in 1833
• Felix Dujardin identified living substance within cells
• Matthias Schleiden, a botanist, and Theodore Schwann, a zoologist, concluded that cells are the basic structural units of both plants and animals
• Rudolf Virchow, a pathologist, proposed that cells arise only from pre-existing cells
• Modern cell theory


  • All organisms consist of one or more cells
  • Cells are the fundamental units of organization in all organisms
  • Cells can only arise from pre-existing cells through division
• Prokaryotic cells


  Cells found in bacteria and archaea
• Eukaryotic cells


  Cells found in protists, fungi, plants, and animals
• Eukaryotic cells possess a nucleus and other membrane-bound organelles, while prokaryotic cells lack a nuclear envelope
• Before 1940, cell structure was limited to what could be seen with light microscopes
• The transmission electron microscope, developed around 1940, allowed for detailed visualization of cell ultrastructure by 1950
• Plasma membrane


  Surrounds all cells and actively controls material movement
• Cell wall


  Made of cellulose, found in plant cells
• Glycocalyx


  Covering on the plasma membrane of many animal cells, providing biochemical identity and containing cell-identity markers under genetic control
• Eukaryotic cells


  • Contain a nucleus where genetic material is housed
  • Contain organelles
• Nucleus


  Contains DNA complexed with proteins and a nucleolus for ribosomal RNA synthesis
• Cytoplasm


  Excluding the nucleus, contains organelles and cytosol
• Cytoskeleton


  Made of microtubules and microfilaments, maintains cell structure
• Organelles


  • Endoplasmic reticulum (smooth and rough)
  • Ribosomes
  • Mitochondria
  • Chloroplasts
• Mitochondria


  Sites of cell respiration
• Chloroplasts


  Involved in photosynthesis
• Centrioles


  Involved in spindle fiber organization during cell division, associated with basal bodies that form cilia and flagella
• Rudolf Virchow, a German physician, is credited with discovering that cells divide and form new cells, a principle known as cell division
• Types of cell division

  • Somatic cell division
  • Reproductive cell division
• Somatic cell division


  Involves mitosis (nuclear division) and cytokinesis (cytoplasmic division), producing two identical cells
• Reproductive cell division


  Involves meiosis, a specialized two-step division that halves the chromosome number
• Mitosis


  • Crucial for all eukaryotic organisms
  • Enables asexual reproduction in some single-celled organisms
  • Supports growth and development in multicellular organisms
  • Aids in wound healing and tissue regeneration in adults
• Mitosis


  1. Genetic material is accurately replicated and divided into two daughter nuclei

  2. Following nuclear division, cytoplasmic division occurs to separate the cells

  3. Each daughter cell receives an equal amount of genetic material as the parent cell
• Cell cycle


  Alternating phases of division and non-division, with interphase being the initial stage between divisions
• Interphase


  1. G1 (gap I) phase

  2. S phase (DNA replication)

  3. G2 (gap II) phase
• Many cell types complete the cell cycle in about 16 hours, with mitosis occupying only a small part
• G0 stage


  Quiescent stage where cells withdraw from the cell cycle
• Mitosis


  1. Prophase

  2. Prometaphase

  3. Metaphase

  4. Anaphase

  5. Telophase
• Prophase


  • Centrioles migrate to opposite ends of the cell
  • Nuclear envelope breaks down and disappears
  • Nucleolus disintegrates
  • Chromatin fibers condense into visible chromosomes
• Sister chromatids


  Chromosomes with identical genetic material, held together by cohesin
• Kinetochore


  Multilayered protein structure at the centromere where spindle fibers bind
• Spindle fibers


  Microtubules made of tubulin protein subunits, grow from centrosomes and connect to kinetochores
• Prometaphase and Metaphase


  1. Chromosomes move to the equatorial plane (metaphase plate)

  2. Spindle fibers bind to chromosomes' kinetochores