Lec 01_ Microscopy and Cell Organelles

Microscopy and Cell Organelles

• Overview: What microscopy is and its significance in biology.

• Historical context: Development of microscopy by early scientists.

What is Microscopy?

• Definition: The field of using microscopes to view microscopic objects.

  • Examples: Bacteria, protists, fungi, amoebas, single-celled organisms.

History of Microscopy

• Invention: Compound microscope invented by Zacharias Janssen around 1600.

• Antonie van Leeuwenhoek:

  • Developed simple microscopes with hand-ground lenses in the 1660s.

  • His microscopes functioned as magnifying glasses with a single lens.

Contributions of Leeuwenhoek

• Magnification: His lenses could magnify objects up to 200 times.

• Observations: Discovered animal and plant tissues, human sperm, blood cells, minerals, and more at a microscopic level.

Understanding Cells

• Definition: The basic building block of all living things and the smallest unit of life capable of independent existence.

• Characteristics of Life:

  • Order, sensitivity, reproduction, adaptation, growth, homeostasis, energy processing, evolution.

Prokaryotic Cells

• Definition: Microscopic single-celled organisms without a distinct nucleus or specialized organelles.

  • Includes: Bacteria, archaea, cyanobacteria.

  • Characteristics:

    • First living organisms.

    • Have a single circular chromosome.

    • Bacterial cell walls made of peptidoglycan.

    • Archaean cell walls made of S layers.

    • Diversity: Thousands of species.

Eukaryotic Cells

• Complexity: Less diverse than prokaryotes but more complex.

• Structure: Compartmentalized into organelles with specific functions.

• Examples: Animalia, Plantae, Fungi, and Protista.

• Efficiency: More efficient at energy production, but require more nutrients.

Endomembrane System

• Definition: Internal membranes involved in cell functions.

• Components:

  • Nuclear envelope, endoplasmic reticulum (ER), Golgi apparatus, lysosomes, vesicles, vacuoles, plasma membrane.

  • Endoplasmic Reticulum (ER): Largest component, extensive network of flattened sacs.

Nucleus

• Function: Contains genetic instructions in DNA, controls cell activities.

  • Chromatin: Long strands of DNA coiled into chromosomes.

• Structure: Enclosed by a double membrane (nuclear envelope).

  • Contains nucleolus where ribosomal RNA (rRNA) is synthesized.

  • Messenger RNA (mRNA) is responsible for directing protein synthesis.

Nucleolus

• Definition: Largest structure in eukaryotic nucleus, vital for ribosome production.

• Function: Participates in stress responses and signal recognition particle formation.

Endoplasmic Reticulum (ER)

• Types:

  • Rough ER:

    • Has ribosomes; involved in protein synthesis and packaging.

  • Smooth ER:

    • No ribosomes; involved in lipid production and processing toxic substances.

Mitochondrion

• Function: Site of cellular respiration, converting food energy to ATP.

• Structure: Enclosed by two phospholipid bilayers, creating intermembrane space and mitochondrial matrix.

  • Matrix contains mitochondrial DNA, ribosomes, and enzymes for cellular respiration reactions.

Golgi Apparatus

• Historical Discovery: Discovered by Camillo Golgi in 1898.

• Function: Processing station for ER products; resembles cell's UPS delivery system.

• Workflow:

  • Receives transport vesicles from ER, modifies products, dispatches them.

Ribosome

• Function: Translates RNA into protein chains, synthesizes polypeptides.

• Structure: Composed of a small subunit (decodes genetic message) and a large subunit (catalyzes peptide bonds).

  • Found in the cytoplasm or attached to rough ER.

Centrioles

• Function: Organelles in cell division forming spindle fibers.

• Structure: Composed mainly of tubulin protein, organizing cell structure and cytoskeleton.

Microtubules

• Definition: Hollow tubes formed from tubulin proteins.

• Functions:

  • Shape and support cells, guide chromosome movement, move materials within cells.

  • Essential for forming spindle fibers during mitosis.

Intermediate Filaments

• Characteristics: Found in most animal cells, made of fibrous proteins.

• Function: Reinforces shape, anchors organelles, generally permanent components.

Microfilaments

• Definition: Solid rods made of actin proteins, forming a network for structural support.

• Function: Aids in cell movement and contraction, particularly in muscle cells.

Cytoplasm

• Definition: Gelatinous liquid filling cells, composed of water, salts, and organic molecules.

• Function: Regulates concentration of solutes and solvent.

Lysosome

• Definition: Membrane-enclosed sac of digestive enzymes.

• Functions:

  • Break down food particles, recycle damaged organelles, destroy engulfed bacteria.

Peroxisome

• Definition: Metabolic compartments that detoxify harmful substances.

• Functions: Break down fatty acids, produce hydrogen peroxide as a byproduct.

Chloroplasts

• Definition: Photosynthesizing organelles in plants and algae.

• Structure: Contains internal membranes with compartments for light absorption and energy conversion.

Extracellular Matrix (ECM)

• Definition: Material produced by cells that helps hold tissues together and supports plasma membranes.

• Components: Primarily glycoproteins, with collagen being the most abundant.

  • Integrins connect ECM with cytoskeleton.

Cell Junctions

• Definition: Specialized connections between neighboring cells in animal tissues.

• Types:

  • Tight junctions: Prevent leakage between cells.

  • Adherens junctions: Cell-cell adhesion complexes.

  • Desmosome junctions: Rivet-like structure for cell stability.

  • Gap junctions: Channels allowing small molecule movement between cells.

Cell Walls in Plants

• Definition: Rigid extracellular structures providing protection and support.

• Structure: Composed of cellulose fibers and layered polysaccharides.

  • Secondary walls form after growth stops, strengthened by lignin.

• Function: Allows nutrient transport through plasmodesmata.