Notes on Cell Structure and Function

Introduction

• Today's topic: Cell Structure and Function
• Key points to discuss:
  • What is a cell?
  • Different types, shapes, and sizes of cells
  • Composition and components of cells

What is a Cell?

• Definition:
  • A cell is the structural and functional unit of life.
  • All living organisms are made up of cells.
• Characteristics:
  • Structural Unit: Forms the structure of all living organisms.
  • Functional Unit: Site of many biochemical reactions (e.g., protein synthesis, energy production).

Discovery of the Cell

• Robert Hooke discovered the cell (cork cells) using a microscope.
• Anton von Leeuwenhoek discovered living cells (protozoans).
• Robert Brown discovered the nucleus.

Cell Theory

1. All living organisms are made up of cells.
2. Cells arise from pre-existing cells (Rudolf Virchow).

Shapes and Sizes of Cells

• Diverse shapes and sizes depending on function and location.
  • Examples:
    • Muscle cells: Spindle-shaped for contraction.
    • Neurons: Long and thin for signal transmission.
    • Sperm cells: Modified for motility.
    • Bacteria: Various shapes (e.g., rod-shaped, spiral).
    • White blood cells: Unique shapes for immune response.

Types of Cells

1. Based on Number of Cells:
   • Unicellular: Organisms made of one cell (e.g., bacteria).
   • Multicellular: Organisms made of multiple cells (e.g., plants, animals).
2. Based on Structure:
   • Prokaryotic: No well-defined nucleus (e.g., bacteria).
   • Eukaryotic: Has a well-defined nucleus (e.g., plants, animals).

Differences Between Prokaryotic and Eukaryotic Cells

• Nucleus:
  • Prokaryotic: Absent
  • Eukaryotic: Present
• Cell Organelles:
  • Prokaryotic: Few organelles
  • Eukaryotic: Numerous organelles
• Cell Type:
  • Prokaryotic: Unicellular
  • Eukaryotic: Unicellular or Multicellular

Prokaryotic Cell Structure

• Components:
  • Flagella: For movement.
  • Pili: Helps in attachment.
  • Cell Wall: Provides protection.
  • Plasma Membrane: Universal protective membrane.
  • Cytoplasm: Contains cell contents.
  • Nucleoid: Contains DNA, no defined nucleus.
  • Ribosomes: For protein synthesis.

Eukaryotic Cell Structure

• Components:
  • Plasma Membrane: Protective layer.
  • Nucleus: Contains genetic material (DNA).
  • Endoplasmic Reticulum (ER):
    • Rough ER: Has ribosomes, synthesizes proteins.
    • Smooth ER: No ribosomes, synthesizes lipids.
  • Golgi Apparatus: Modifies and packages proteins and lipids.
  • Mitochondria: Powerhouse of the cell, produces ATP.
• Plant cells have:
  • Cell Wall: Made of cellulose, provides protection.
  • Vacuoles: Storage structure, 80% of cell volume.
  • Plastids: Contain pigments, e.g., chloroplasts for photosynthesis.

Functions of Cell Organelles

• Plasma Membrane: Protection and transportation of substances.
• Cytoplasm: Medium for biochemical reactions.
• Nucleus: Controls cell activities, houses genetic material.
• Endoplasmic Reticulum: Synthesizes proteins and lipids.
• Golgi Apparatus: Processes and packages proteins.
• Mitochondria: Produces energy (ATP).
• Cell Wall: Provides structural support.
• Vacuoles: Storage of nutrients and waste.
• Plastids: Store pigments and aid in photosynthesis.

Conclusion

• Review the structural and functional aspects of cells.
• Understand the diversity in cell types, shapes, and sizes based on function.