History and Definition of Cells

History of Cell Study

• Robert Hooke (1665) coined the term "cell" while examining cork cells.
• Antonie van Leeuwenhoek developed optics to visualize single cells; his technology was lost for nearly 200 years.
• Robert Brown (1831) discovered the "nucleus" within cells.
• Theodor Schwann (1838) viewed animal cells and concluded that cells are elementary particles in all life forms.
• Mattias Schleiden proposed that cells are the fundamental basis of life.
• Rudolf Virchow (1858) stated that all cells arise from preexisting cells.
• Cell theory established three key principles:
  • All living organisms are composed of one or more cells.
  • Cells are the basic unit of structure and function.
  • All cells originate from existing cells.

Definition of Cell

• A cell is the smallest unit capable of performing life functions.
• Examples include:
  • Amoeba Proteus
  • Plant Stem Cells
  • Bacteria
  • Red Blood Cells
  • Nerve Cells

Types of Cells

• Prokaryotic Cells:

  • Lack membrane-bound structures.
  • Few internal components.
  • Examples include bacteria.

• Eukaryotic Cells:

  • Contain organelles surrounded by membranes.
  • Comprise most living organisms, including plants and animals.

Common Cell Structures

• Found in both Plant and Animal Cells:

  • Nucleus
  • Golgi Complex
  • Mitochondrion
  • Lysosomes
  • Endoplasmic Reticulum
  • Cell Membrane
  • Ribosomes
  • Vacuoles

• Unique to Plant Cells:

  • Chloroplasts
  • Cell Wall

Cell Components

• Cell Membrane:

  • Outer membrane controlling the movement of substances in and out of the cell.
  • Composed of a double lipid layer.

• Cell Wall:

  • Predominantly found in plant cells and bacteria.
  • Provides structural support and protection.

• Nucleus:

  • Directs cell activities and contains genetic material (DNA).
  • Surrounded by a nuclear membrane.

• Nuclear Membrane:

  • Composed of two layers with openings for material exchange.

• Chromosomes:

  • Located in the nucleus, made of DNA, containing genetic instructions.

• Nucleolus:

  • Found within the nucleus, involved in RNA production for protein synthesis.

• Cytoplasm:

  • Gel-like substance filled with hereditary material, lies between the nucleus and the cell membrane.

• Endoplasmic Reticulum (ER):

  • Network for transporting materials within the cell.
  • Smooth ER lacks ribosomes, while Rough ER has ribosomes on its surface.

• Ribosomes:

  • Sites for protein synthesis, numerous in every cell.

• Mitochondria:

  • Powerhouses of the cell, generating energy through chemical reactions.

• Golgi Bodies:

  • Function in packaging proteins and transporting materials within and outside the cell.

• Lysosomes:

  • Digestive organelles, breaking down waste and recycling cellular components.

• Vacuoles:

  • Membrane-bound sacs for storage, digestion, and waste removal; help maintain plant cell shape.

• Chloroplasts:

  • Photosynthesis occurs here in plant cells, containing chlorophyll.

Macromolecules

• Macromolecules are crucial for human body functions:
  • Carbohydrates: Main energy source, consists of carbon, hydrogen, and oxygen in a 1:2:1 ratio. Examples: glucose (simple sugar), starch (complex carbohydrates).
  • Lipids: Provide stored energy, insulation, and assist vitamin absorption, built from triglycerides.
  • Proteins: Essential for growth and repair; made of amino acids forming polypeptides, broken down by enzymes into individual amino acids.
  • Nucleic Acids: Store and carry genetic information, composed of nucleotides; includes DNA, not obtained from food sources.

Enzymes

• Enzymes are proteins that act as catalysts, speeding up chemical reactions by lowering the activation energy needed.
• Each enzyme is specific to its substrate, and enzyme activity can be influenced by temperature and pH.