cell the unit of life]

UNIT 3: Cell and Molecular Biology

Introduction to Biology

  • Biology studies living organisms.

  • The cell theory underscores the cellular organization that unites diverse forms of life.

  • Understanding cellular structure and division is crucial in biological sciences.

  • Exploring physiological and behavioral processes is guided by the integrity of cellular organization.

  • The physico-chemical approach using cell-free systems sheds light on the molecular basis of life activities, such as digestion and memory.

  • This approach is known as Reductionist Biology, employing physics and chemistry principles.

  • References to biomolecules can be found in Chapter 9.

G.N. Ramachandran: Pioneer in Protein Structure

  • Founder of the 'Madras school' of biopolymer conformational analysis.

  • Key contributions:

    • Discovered triple helical structure of collagen (1954).

    • Developed the Ramachandran plot for protein conformation analysis.

  • Early life and education:

    • Born: October 8, 1922, near Cochin, India.

    • Influenced by his father's academic background in mathematics.

    • Graduated top of his Physics course from the University of Madras (1942).

    • Ph.D. from Cambridge University (1949), influenced by Linus Pauling's work.

  • Passed away: April 7, 2001.

What is a Cell?

  • **All living organisms are composed of cells: **

    • Unicellular organisms: Independently capable of essential life functions.

    • Multicellular organisms: Composed of multiple cells.

  • Anton Von Leeuwenhoek was the first to observe live cells.

  • The microscope advancement revealed cell structure details.

Cell Theory

  • Key figures: Matthias Schleiden & Theodor Schwann.

    • Schleiden (1838): All plant tissues consist of cells.

    • Schwann (1839): Proposed cell theory supporting the existence of plasma membranes and cell walls in different organisms.

  • Rudolf Virchow (1855): Introduced the idea that all cells arise from pre-existing cells.

  • Modern cell theory includes:

    1. All living organisms are composed of cells and cellular products.

    2. All cells arise from pre-existing cells.

Overview of Cell Structure

  • Cell Types: Eukaryotic and Prokaryotic.

    • Eukaryotic: Defined by membrane-bound nuclei and organelles, complex structures.

    • Prokaryotic: Lack a membrane-bound nucleus, simpler structure.

  • Common components include:

    • Nucleus: Stores genetic material.

    • Cytoplasm: Site for cellular reactions.

    • Cell Membrane: Selectively permeable barrier.

    • Organelles: Specialized structures for various functions.

Cellular Characteristics

  • Prokaryotic cells:

    • Generally smaller, lack membrane-bound organelles.

    • Genetic material is circular (plasmid) and naked.

  • Eukaryotic cells:

    • Larger, complex with various organelles (e.g., mitochondria, Golgi apparatus).

Cell Organelles and Functions

1. Cell Membrane

  • Composed predominantly of phospholipids and proteins.

  • Functions:

    • Selective permeability.

    • Cell signaling and communication.

2. Cell Wall

  • Provides structural support and protects against mechanical stresses.

  • Composition varies:

    • Plants: Primarily cellulose, hemicellulose.

    • Fungi: Chitin.

3. Endoplasmic Reticulum (ER)

  • Network of tubular structures:

    • Rough ER: Studded with ribosomes, involved in protein synthesis.

    • Smooth ER: Lacks ribosomes, synthesizes lipids.

4. Golgi Apparatus

  • Series of stacked membranes that enhance protein processing and sorting.

  • Responsible for packaging and dispatching materials in vesicles.

5. Lysosomes

  • Contains hydrolytic enzymes for digestion of macromolecules.

  • Functions in waste disposal and recycling cellular components.

6. Mitochondria

  • Known as the 'powerhouse of the cell.'

  • Site of aerobic respiration, convert energy into ATP.

7. Plastids

  • Present in plant cells:

    • Chloroplasts: Photosynthesis.

    • Chromoplasts: Pigment storage.

    • Leucoplasts: Store starch, oils, and proteins.

8. Ribosomes

  • Sites of protein synthesis, composed of RNA and proteins, exist in prokaryotic and eukaryotic cells.

  • Eukaryotic ribosomes (80S) versus prokaryotic ribosomes (70S).

9. Cytoskeleton

  • Provides structural support, aids in motility.

  • Composed of microtubules, microfilaments, and intermediate filaments.

10. Nucleus

  • Contains chromatin and nucleolus.

  • Nuclear envelope separates nucleoplasm from cytoplasm.

11. Centrioles and Centrosome

  • Centrioles are involved in cell division and form bases for cilia/flagella.

Summary

  • Cells are the fundamental units of life, performing all vital functions.

  • Eukaryotic cells are defined by their complex structures while prokaryotic cells are simpler.

  • Organelles within eukaryotic cells perform specialized functions and are important for the overall activities of the cell.