Cell Biology Lecture Notes

Introduction to Biology

  • Biology is the science that deals with the study of living organisms.
  • It has branches like Botany (study of plants), Zoology (study of animals), and Microbiology (study of microorganisms).

The Cell: The Fundamental Unit of Life

  • Definition: The cell is the basic structural and functional unit of life.
  • Analogy: Just as bricks are the basic unit of a building, cells are the basic unit of living organisms.
  • Cytology: The study of cells.

Levels of Structural Organization

  • Cell → Tissue → Organ → Organ System → Organism
  • Cell: Basic structural and functional unit.
  • Tissue: Group of cells with similar structures, working together to perform a shared function.
  • Organ: Structure made up of a group of tissues, working together to perform specific functions (e.g., Brain, Heart, Kidney, Liver, Lungs).
  • Organ System: Group of organs with related functions, working together to perform body functions (e.g., Digestive system, Respiratory System, Excretory System, Circulatory System).
  • Organism: Living thing performing all life processes.

Discovery of Cells and Cell Theory

Robert Hooke (1665)

  • Discovered cells (dead cells) in a thin slice of cork.
  • Coined the term "cell".
  • Observed little boxes/compartments under a self-designed microscope.
  • The term "cell" comes from the Latin word for small compartments.
  • Cork is the outermost layer (bark) of an Oak Tree.

Antonie Van Leeuwenhoek (1674)

  • Discovered living cells.
  • Observed green algae (Spirogyra) in pond water.

Robert Brown (1831)

  • Discovered the nucleus in cells.
  • Observed orchid cells.

Purkinji (1839)

  • Coined the term "Protoplasm" to refer to the living content of the cell.

Cell Theory

  • Matthias Schleiden (Botanist, 1838) & Theodore Schwann (Zoologist, 1839):
    • All plants and animals are made up of cells.
  • Rudolf Virchow (1855):
    • Omnis cellula-e-cellula: All cells come from pre-existing cells.

Microscopy

  • Compound microscope and Light microscope are used to observe cells.
  • Electron microscope (developed around 1940).
  • Parts of a Compound Microscope: Eyepiece, Body tube, Coarse adjustment, Fine adjustment, Arm, Objective lens, Clip, Microscope slide, Stage, Swivel, Condenser, Cell, Nucleus, Mirror, Base.

Variety in Cell Number, Shape, and Size

Cell Number

  • Unicellular Organisms:
    • Made up of only a single cell.
    • Examples: Bacteria, Amoeba, Paramoecium, Chlamydomonas (Algae), Yeast (Fungi).
  • Multicellular Organisms:
    • Made up of many (more than one) cells.
    • Examples: Plants, Animals, Human beings.

Cell Shape

  • Various cell shapes related to their function.
    • Nerve Cell (Neuron): Long and branched (Brain + Spinal cord).
    • Human Red Blood Cells: Biconcave.
    • Smooth Muscle Cells: Spindle shape.
    • Ovum/Egg Cell: Spherical.
    • Sperm Cell: Elongated.
  • Some cells can change their shape (e.g., Amoeba, Human White blood cells).

Cell Size

  • Mycoplasma: Smallest living cell.
  • Egg of an Ostrich: Largest living cell.
  • PPLO (Pleuro Pneumonia Like Organisms)

Structural Organization of a Cell

  • Basic Components:
    • Plasma Membrane/Cell Membrane
    • Cell Wall (in plants)
    • Nucleus
    • Cytoplasm
    • Cell Organelles

Plasma Membrane/Cell Membrane

  • Outermost covering of the cell.
  • Permits the entry and exit of some materials (selectively permeable).

Cell Wall

  • Rigid outer covering lying outside the plasma membrane.
  • Present in plants only.

Nucleus

  • Has a double-layered nuclear membrane with nuclear pores for transfer of material.
  • Contains chromosomes.

Cytoplasm

  • Fluid content inside the plasma membrane and outside the nucleus.
  • Contains cell organelles.

Cell Organelles

  • Specialized membrane-bound parts of the cell present in the cytoplasm.
  • Examples: Golgi apparatus, Smooth endoplasmic reticulum, Rough endoplasmic reticulum, Lysosome, Ribosomes, Mitochondrion, Chloroplast (in plant cells), Centriole.

Cell Wall Composition

  • Non-living and rigid.
  • Forms outer covering of the plasma membrane.
  • Provides shape to the cell.
  • Protects cell from mechanical damage and infection.
  • Present in Plants, Bacteria, and Fungi.
  • Absent in Animals and Viruses.

Additional Notes

  • Cell wall of plant cell is made up of Cellulose. Other options include Chitin and Peptidoglycan.
  • Homework questions:
    1. Longest cell in the human body
    2. Largest cell in the human body
    3. Smallest cell in the human body (PPLO)