BIO 1550 Microbiology Midterm 1 Comprehensive Study Notes

Introduction to Microbiology

Historical Experiments Disproving Spontaneous Generation

• Francesco Redi’s Experiment: Redi demonstrated that maggots on decaying meat arose from eggs laid by flies, not from the meat itself. He covered some jars with gauze, leaving others open; only the open jars developed maggots.

• Principle: Life does not spontaneously arise from non-living matter; it originates from pre-existing life.

• Louis Pasteur’s Experiment: Pasteur used swan-necked flasks containing broth. After boiling, the broth remained sterile unless the flask was tilted, allowing airborne particles to enter.

• Principle: Microorganisms are present in the air and can contaminate sterile solutions, but life does not spontaneously generate.

Aseptic Technique

• Definition: Procedures used to prevent contamination by unwanted microorganisms.

• Application: Essential in laboratory work, medical procedures, and food production to maintain sterility.

Invention of the Microscope

• Inventor: Antonie van Leeuwenhoek is credited with developing the first practical microscopes and observing microorganisms, which he called "animalcules." Robert Hooke also contributed by describing cells.

Benefits of Microorganisms

• Decomposition: Microbes break down dead organic matter, recycling nutrients.

• Food Production: Used in fermentation (e.g., yogurt, cheese, bread).

• Biotechnology: Production of antibiotics, enzymes, and other chemicals.

• Symbiosis: Normal microflora aid in digestion and protect against pathogens.

Classification of Microorganisms

Three Domains of Life

• Bacteria: Prokaryotic, cell walls contain peptidoglycan.

• Archaea: Prokaryotic, cell walls lack peptidoglycan, often found in extreme environments (e.g., hot springs, salt lakes).

• Eukarya: Eukaryotic organisms, including algae, fungi, protozoa, and animals.

Archaea

• Characteristics: Unicellular, prokaryotic, lack peptidoglycan in cell walls.

• Habitats: Extreme environments such as high temperature (thermophiles), high salt (halophiles), and acidic conditions (acidophiles).

Cell Structure and Function

Bacterial Cell Components

• Cell Wall: Contains peptidoglycan, provides shape and protection.

• Nucleoid: Region containing the bacterial chromosome (DNA).

• Ribosomes: Sites of protein synthesis (70S type in prokaryotes).

• Other Structures: Plasmids, flagella, pili, capsules.

Peptidoglycan

• Location: Found in bacterial cell walls (not in Archaea or Eukarya).

• Function: Provides rigidity and protection against osmotic pressure.

Gram Staining

• Concept: Differential staining technique to classify bacteria as Gram-positive or Gram-negative based on cell wall structure.

• Gram-Positive: Thick peptidoglycan layer, stains purple.

• Gram-Negative: Thin peptidoglycan layer, outer membrane present, stains pink/red.

Acid-Fast Staining

• Concept: Identifies bacteria with waxy cell walls (e.g., Mycobacterium species).

• Result: Acid-fast bacteria retain red dye; non-acid-fast bacteria take up blue counterstain.

Microflora (Normal Flora)

• Definition: Microorganisms that normally inhabit the human body without causing disease.

• Functions: Compete with pathogens, aid in digestion, synthesize vitamins.

Algae, Fungi, and Protozoa

• Algae: Photosynthetic, eukaryotic, aquatic, cell walls of cellulose.

• Fungi: Eukaryotic, non-photosynthetic, cell walls of chitin, includes yeasts and molds.

• Protozoa: Unicellular, eukaryotic, lack cell walls, often motile.

Viruses, Prions, and Viroids

• Viruses: Acellular, ultramicroscopic (20–300 nm), consist of DNA or RNA core surrounded by protein coat, require host cells to replicate.

• Prions: Infectious proteins causing neurodegenerative diseases (e.g., Creutzfeldt-Jakob disease).

• Viroids: Infectious RNA molecules, lack protein coat, cause plant diseases.

Chemical Principles of Microbiology

Chemical Bonds

• Ionic Bonds: Formed by transfer of electrons from one atom to another, resulting in charged ions (e.g., NaCl).

• Covalent Bonds: Formed by sharing of electrons between atoms (e.g., H2O, CH4).

• Polar Bonds: Unequal sharing of electrons, resulting in partial charges (e.g., H2O).

• Non-Polar Bonds: Equal sharing of electrons (e.g., O2, N2).

• Hydrogen Bonds: Weak attraction between a hydrogen atom (covalently bonded to O or N) and another electronegative atom. Important in water, DNA, and protein structure.

Macromolecules

• Amino Acids and Proteins: Amino acids are building blocks of proteins, linked by peptide bonds. Proteins have four levels of structure: primary (sequence), secondary (alpha-helix, beta-sheet), tertiary (3D folding), and quaternary (multiple polypeptides).

• Protein Denaturation: Loss of protein structure (and function) due to heat, pH, or chemicals.

• Enzymes: Biological catalysts that speed up reactions by lowering activation energy.

• Activation Energy: Minimum energy required for a reaction to proceed.

• Carbohydrates: Sugars and polymers of sugars; formed by dehydration synthesis, broken down by hydrolysis. Glycosidic bonds link monosaccharides.

• Peptide Bonds: Link amino acids in proteins; formed by dehydration synthesis.

• Dehydration and Hydrolysis: Dehydration removes water to form bonds; hydrolysis adds water to break bonds.

• Nucleic Acids: DNA and RNA; DNA is double-stranded with A:T and G:C base pairing.

• Lipids: Three main types: triglycerides (energy storage), phospholipids (membranes), steroids (hormones). Lipids are nonpolar and hydrophobic.

Cell Membrane and Transport

Phospholipids and Membrane Structure

• Phospholipids: Major component of cell membranes; found in all cellular membranes.

• Arrangement: Hydrophilic (water-loving) heads face outward; hydrophobic (water-fearing) tails face inward, forming a bilayer.

• Fluid Mosaic Model: Describes the membrane as a dynamic structure with proteins embedded in or attached to a fluid lipid bilayer.

• Membrane Proteins: Serve as channels, receptors, enzymes, and structural components.

Transport Mechanisms

• Osmosis: Diffusion of water across a selectively permeable membrane from low to high solute concentration.

• Passive Transport: Movement of substances down their concentration gradient without energy input (e.g., diffusion, facilitated diffusion).

• Active Transport: Movement of substances against their concentration gradient, requiring energy (ATP).

• Exocytosis and Endocytosis: Bulk transport mechanisms; exocytosis expels materials, endocytosis brings materials into the cell.

• Phagocytosis: "Cell eating"; uptake of large particles.

• Pinocytosis: "Cell drinking"; uptake of fluids and dissolved substances.

Prokaryotic and Eukaryotic Cell Structures

Gram-Positive vs. Gram-Negative Cell Walls

Feature	Gram-Positive	Gram-Negative
Peptidoglycan Layer	Thick	Thin
Outer Membrane	Absent	Present
Teichoic Acids	Present	Absent
Lipopolysaccharide (LPS)	Absent	Present
Stain Color	Purple	Pink/Red

Endospores

• Definition: Highly resistant, dormant structures formed by some bacteria (e.g., Bacillus, Clostridium) to survive harsh conditions.

Eukaryotic Organelles and Functions

• Nucleus: Contains genetic material (DNA).

• Mitochondria: Site of ATP production (cellular respiration).

• Endoplasmic Reticulum (ER): Synthesis of proteins (rough ER) and lipids (smooth ER).

• Golgi Apparatus: Modifies, sorts, and packages proteins and lipids.

• Lysosomes: Contain digestive enzymes for breakdown of macromolecules.

• Chloroplasts: Site of photosynthesis in plants and algae.

• Vacuoles: Storage and structural support (especially in plants).