Microbiology Unit 1: Introduction, Cell Structure, Microscopy, Prokaryotes, Eukaryotes, Viruses & Prions

Introduction to Microbiology

Importance of Microbiology

Microbiology is the study of microscopic organisms, including bacteria, viruses, fungi, and protozoa. It is crucial in medicine, environmental science, biotechnology, and food production.

• Medical Importance: Understanding pathogens, disease mechanisms, and antibiotic development.

• Environmental Importance: Microbes recycle nutrients, degrade pollutants, and maintain ecosystem balance.

• Industrial Importance: Used in fermentation, bioremediation, and production of pharmaceuticals.

• Biotechnological Applications: Genetic engineering, enzyme production, and synthetic biology.

Cell Theory and Germ Theory

Cell theory states that all living things are composed of cells, and cells are the basic unit of life. Germ theory proposes that microorganisms cause disease.

• Evidence: Microscopy, experiments by Louis Pasteur and Robert Koch.

• Applications: Sterilization, vaccination, and hygiene practices.

Spontaneous Generation

Spontaneous generation was the belief that life could arise from non-living matter. It was disproved by experiments (e.g., Pasteur's swan-neck flask experiment).

• Key Experiment: Pasteur showed that sterilized broth remained free of microbes unless exposed to air.

Naming Living Things & Tree of Life Hierarchies

Organisms are named using binomial nomenclature (Genus species). The tree of life classifies organisms based on evolutionary relationships.

• Hierarchies: Domain, Kingdom, Phylum, Class, Order, Family, Genus, Species.

• Domains: Bacteria, Archaea, Eukarya.

• Purpose: Reflects genetic and evolutionary relationships.

Sorting Microorganisms by Cell Structure

• Prokaryotes: Bacteria and Archaea; lack membrane-bound organelles.

• Eukaryotes: Fungi, protozoa, algae; have membrane-bound organelles.

Cell Structure

Endosymbiotic Theory

The endosymbiotic theory explains the origin of mitochondria and chloroplasts in eukaryotic cells.

• Key Points: These organelles were once free-living prokaryotes engulfed by ancestral eukaryotes.

• Evidence: Double membranes, own DNA, ribosomes similar to prokaryotes.

Membrane Transport

Membrane transport refers to the movement of substances across the cell membrane.

• Passive Transport: No energy required; includes diffusion, osmosis, and facilitated diffusion.

• Active Transport: Requires energy (ATP); moves substances against concentration gradients.

• Importance: Maintains homeostasis, nutrient uptake, waste removal.

Concentration Gradients

• High Concentration: Area with more particles.

• Low Concentration: Area with fewer particles.

• Diffusion: Movement from high to low concentration.

Phospholipids and Their Properties

• Structure: Hydrophilic head, hydrophobic tails.

• Function: Form bilayer, barrier to water-soluble substances.

Components Found in All Cells

• Cell Membrane: Controls entry/exit of substances.

• Cytoplasm: Site of metabolic activity.

• Genetic Material: DNA or RNA.

• Ribosomes: Protein synthesis.

Osmosis and Solutions

Osmosis is the diffusion of water across a semipermeable membrane.

• Isotonic Solution: Equal solute concentration; no net water movement.

• Hypotonic Solution: Lower solute concentration outside; water enters cell, may cause lysis.

• Hypertonic Solution: Higher solute concentration outside; water leaves cell, may cause shrinkage.

• Effect on Cells: Cell volume changes depending on solution type.

Prokaryotic vs Eukaryotic Cell Traits

• Prokaryotes: No nucleus, no membrane-bound organelles, smaller size.

• Eukaryotes: Nucleus, membrane-bound organelles, larger size.

Cell Walls

• Bacteria: Peptidoglycan cell wall.

• Fungi: Chitin cell wall.

• Plants: Cellulose cell wall.

• Animals: No cell wall.

Microscopy

Staining Techniques

Staining enhances contrast in microscopy.

• Simple Staining: Uses one dye; reveals cell shape and arrangement.

• Differential Staining: Uses multiple dyes; distinguishes cell types (e.g., Gram stain).

Gram Staining

Gram staining differentiates bacteria based on cell wall structure.

• Gram Positive: Thick peptidoglycan, retains crystal violet, appears purple.

• Gram Negative: Thin peptidoglycan, outer membrane, loses crystal violet, appears pink/red.

Prokaryotic Cells

Adaptations to Harsh Environments

• Endospores: Resistant to heat, desiccation, chemicals.

• Capsules: Protect against immune response.

• Flagella: Motility.

Cell Wall Structure

• Gram Positive: Thick peptidoglycan, teichoic acids.

• Gram Negative: Thin peptidoglycan, outer membrane, lipopolysaccharides.

Cell Shape and Arrangement

• Coccus: Spherical.

• Bacillus: Rod-shaped.

• Spirillum: Spiral-shaped.

• Arrangements: Strepto- (chains), Staphylo- (clusters), Diplo- (pairs).

Unique Prokaryotic Structures

• Pili: Attachment and conjugation.

• Plasmids: Extra-chromosomal DNA.

• Nucleoid: Region containing DNA.

Eukaryotic Cells

Organelles and Their Functions

• Nucleus: Contains genetic material.

• Mitochondria: ATP production.

• Endoplasmic Reticulum: Protein and lipid synthesis.

• Golgi Apparatus: Modifies and packages proteins.

• Lysosomes: Digestion of cellular waste.

• Chloroplasts: Photosynthesis (in plants and algae).

Cytoskeleton Types and Functions

• Microtubules: Cell shape, transport, division.

• Microfilaments: Movement, support.

• Intermediate Filaments: Structural stability.

Viruses and Prions

Characteristics of Viruses

• Structure: DNA or RNA core, protein coat (capsid), sometimes envelope.

• Obligate Intracellular Parasites: Require host cell to reproduce.

• No Cellular Structure: Not considered living.

Prions

• Definition: Infectious proteins causing neurodegenerative diseases.

• Examples: Creutzfeldt-Jakob disease, mad cow disease.

• Unique Feature: No nucleic acids; cause disease by inducing misfolding of normal proteins.