Unit 3: Cellular Organization of Life Forms

Overview

• Biology focuses on the study of living organisms, emphasizing the cellular organization common to all life forms.
• Cell theory highlights the unity among diverse life forms, underscoring the cellular basis of physiological and behavioral processes.
• Reductionist Biology: Utilizes physico-chemical approaches to understand biological processes at the molecular level.

Chapters

1. Cell: Structure and Functions
   • Chapter 8: Cell: The Unit of Life
   • Chapter 9: Biomolecules
   • Chapter 10: Cell Cycle and Cell Division

G.N. Ramachandran

• Prominent in protein structure, known for discovering the triple helical structure of collagen.
• Significant contributions to structural biology with the Ramachandran plot.

Chapter 8: Cell: The Unit of Life

8.1 What is a Cell?

• Fundamental unit of life, capable of independent existence and performing life functions.
• Historical insights: Antonie Von Leeuwenhoek (live cell), Robert Brown (nucleus).
• Microscopy advancements revealed cell structure details.

8.2 Cell Theory

• Schleiden and Schwann proposed that all organisms are composed of cells.
• Rudolf Virchow added that all cells arise from pre-existing cells.
• Modern understanding: Cells are the basic unit of life and originate from existing cells.

8.3 An Overview of Cell

• Plant cells have a cell wall; animal cells have a plasma membrane.
• Eukaryotic cells have membrane-bound nuclei; prokaryotic cells do not.
• Organelles like ER, Golgi complex, mitochondria, etc., are present in eukaryotes.

8.4 Prokaryotic Cells

• Represented by bacteria, cyanobacteria, mycoplasma, PPLO.
• Lack a defined nucleus, containing naked DNA and plasmids.
• Cell envelope: Includes glycocalyx, cell wall, and plasma membrane.
• Unique structures: Ribosomes, mesosomes, flagella, pili, and fimbriae.

8.4.1 Cell Envelope and Modifications

• Gram-positive and Gram-negative bacteria classification based on cell envelope.
• Glycocalyx can be a slime layer or a capsule.

8.5 Eukaryotic Cells

• Includes protists, plants, animals, fungi with complex organelles.
• Plant cells: Contain cell walls, plastids, large vacuoles.
• Animal cells: Have centrioles.

8.5.1 Cell Membrane

• Composed of a lipid bilayer with proteins, adhering to the fluid mosaic model.
• Functions in selective permeable transport, including passive and active transport mechanisms.

8.5.2 Cell Wall

• Provides structural support, protection, and interaction between cells.
• Varied composition in algae and plants.

8.5.3 Endomembrane System

• Includes ER, Golgi complex, lysosomes, and vacuoles.
• ER types: Rough (protein synthesis) and Smooth (lipid synthesis).
• Golgi apparatus: Modifies and packages proteins.
• Lysosomes: Contain hydrolytic enzymes.
• Vacuoles: Storage, osmoregulation, and excretion.

8.5.4 Mitochondria

• Known as the powerhouse of the cell, site of ATP production.
• Double membrane bound with internal cristae.

8.5.5 Plastids

• Chloroplasts (photosynthesis), chromoplasts (pigments), leucoplasts (storage).

8.5.6 Ribosomes

• Sites of protein synthesis; differ in prokaryotes (70S) and eukaryotes (80S).

8.5.7 Cytoskeleton

• Network of microtubules, microfilaments providing support and shape.

8.5.8 Cilia and Flagella

• Extensions for movement, structurally different in prokaryotes and eukaryotes.

8.5.9 Centrosome and Centrioles

• Involved in cell division, forming spindle fibers.

8.5.10 Nucleus

• Enclosed by a double membrane, containing nucleoplasm, chromatin, and nucleoli.
• Site of RNA synthesis and controls cellular activities.

8.5.11 Microbodies

• Enzyme-containing vesicles present in both plant and animal cells.

Summary

• Cells are the basic structural and functional units of life.
• Eukaryotic cells feature membrane-bound organelles; prokaryotic cells do not.
• Cell membrane, nucleus, and cytoplasm are fundamental components.
• Organelles like mitochondria, chloroplasts, ER, Golgi apparatus, etc., perform specific cellular functions.