Microbiology exam 2 review revie

3.1 Spontaneous Generation

  • The theory of spontaneous generation states that life arose from nonliving matter.
    • This belief was long-held, dating back to Aristotle and the ancient Greeks.
  • Francesco Redi's Experiment (17th Century)
    • Presented the first significant evidence refuting spontaneous generation.
    • Showed that flies must have access to meat for maggots to develop on the meat.
  • Prominent Scientists' Arguments
    • John Needham: Presented arguments in support of spontaneous generation.
    • Lazzaro Spallanzani: Conducted experiments against spontaneous generation.
  • Louis Pasteur's Contribution
    • Credited with conclusively disproving the theory of spontaneous generation with his swan-neck flask experiment.
    • Proposed the idea that "life only comes from life."

3.2 Foundations of Modern Cell Theory

  • Cells were first observed in the 1660s by Robert Hooke, but cell theory was not widely accepted for another 200 years.
  • Key Contributors to Cell Theory:
    • Schleiden, Schwann, Remak, and Virchow all contributed to the acceptance of cell theory.
  • Endosymbiotic Theory
    • States that mitochondria and chloroplasts have origins in bacteria.
    • Supported by significant structural and genetic information.
  • Miasma Theory vs. Germ Theory of Disease
    • Miasma theory was predominant until the 19th century.
    • Germ theory, developed by Semmelweis, Snow, Pasteur, Lister, Koch, and others, replaced miasma theory.

3.3 Unique Characteristics of Prokaryotic Cells

  • Genetic Material
    • Prokaryotic cells contain genetic material in a nucleoid, unlike eukaryotic cells that possess a membrane-bound nucleus.
  • Lack of Organelles
    • Generally lack membrane-bound organelles.
  • Morphology and Arrangement
    • Prokaryotic cells of the same species typically have similar cell morphology and cellular arrangement.
  • Cell Wall Composition
    • Most prokaryotic cells have a cell wall that maintains morphology and protects against osmotic pressure.
  • Extrachromosomal DNA
    • Can contain plasmids outside of the nucleoid.
  • Ribosome Size
    • Prokaryotic ribosomes measured at 70S.

Prokaryotic Cell Features (Continued)

  • Inclusions
    • Prokaryotic cells can have inclusions that store nutrients or chemicals.
  • Endospores
    • Formed through sporulation to survive in dormant states during unfavorable conditions.
    • Endospores can germinate into vegetative cells under favorable conditions.
  • Cell Envelope
    • Consists of a plasma membrane and usually a cell wall.
  • Membrane Composition
    • Bacterial membranes are made of phospholipids with integral or peripheral proteins; fatty acids are ester-linked.
    • Archaeal membranes differ by being composed of ether-linked fatty acids.
  • Transport Mechanisms
    • Small molecules can diffuse through the membrane; large molecules require active transport using energy.
  • Cell Wall Variations
    • Composed of peptidoglycan in bacteria and pseudopeptidoglycan in archaea.
  • Gram Staining
    • Gram-positive bacteria have a thick peptidoglycan layer.
    • Gram-negative bacteria possess a thin peptidoglycan layer with an outer membrane.
  • Glycocalyx Coatings
    • Some prokaryotic cells produce glycocalyx coatings (capsules/slime layers) for surface attachment and immune evasion.
  • Fimbriae and Pili
    • Fimbriae or pili help in surface attachment; pili facilitate genetic material transfer between cells.
  • Flagella
    • Used for locomotion; peritrichous bacteria display numerous flagella aiding movement toward attractants through runs and tumbles.

3.4 Unique Characteristics of Eukaryotic Cells

  • Definition
    • Eukaryotic cells possess a nucleus bound by a nuclear envelope (two lipid bilayers).
  • Morphological Variability
    • Cell morphologies vary widely, maintained by the cytoskeleton, cell membrane, and/or cell wall.
  • Nucleolus
    • Located within the nucleus, it is the site for ribosomal synthesis and assembly.
  • Ribosome Size
    • Eukaryotic cells contain 80S ribosomes; 70S ribosomes are found in mitochondria and chloroplasts.
  • Endomembrane System
    • Eukaryotic cells evolved an endomembrane system consisting of membrane-bound organelles for transport (e.g., vesicles, endoplasmic reticulum, Golgi apparatus).
  • Smooth vs. Rough Endoplasmic Reticulum
    • Smooth ER: Involved in lipid biosynthesis, carbohydrate metabolism, and detoxification.
    • Rough ER: Contains 80S ribosomes; synthesizes membrane-bound proteins.
  • Golgi Apparatus
    • Processes proteins and lipids, typically adding sugar molecules to form glycoproteins or glycolipids.
  • Lysosomes
    • Contain enzymes that break down ingested particles, phagocytosed cells, and damaged components.
  • Cytoskeleton
    • Composed of microfilaments, intermediate filaments, and microtubules, providing structural support and transport capabilities.
  • Centrosomes
    • Microtubule-organizing centers important for mitotic spindle formation during mitosis.
  • Mitochondria
    • Sites of cellular respiration; have outer and inner membranes, with the inner enclosing cristae and the matrix.
  • Plasma Membrane Structure
    • Similar to prokaryotic membranes but contains sterols, glycoproteins, and glycolipids for recognition purposes.
  • Transport Mechanisms
    • Eukaryotic membranes can utilize active transport, passive transport, endocytosis, and exocytosis.
  • Cell Walls vs. Extracellular Matrix
    • Fungi, algae, plants, and some protists have cell walls; animals and some protozoans have a sticky extracellular matrix for support and signaling.
  • Flagella and Cilia
    • Eukaryotic flagella differ structurally from prokaryotic flagella, as do cilia, which are used for locomotion and movement of particles.

4.1 Prokaryote Habitats, Relationships, and Microbiomes

  • Prokaryotes are unicellular microorganisms without a nucleus.
  • Ubiquity
    • Found in diverse environments, including extreme conditions.
  • Metabolic Flexibility
    • Adjust feeding methods based on available resources.
  • Communities
    • Live in communities interacting with larger organisms like humans.
  • Human Microbiome
    • The totality of prokaryotes living on the human body, varying by body region and individual,
    • The microbiota refers to specific populations in certain areas of the body (e.g., mouth, gut).
  • Classification
    • Prokaryotes are classified into domains Archaea and Bacteria.

4.2 Proteobacteria

  • Definition
    • A phylum of gram-negative bacteria discovered by Carl Woese in the 1980s.
  • Classification
    • Divided into classes: alpha, beta, gamma, delta, and epsilonproteobacteria, each with distinct orders, families, genera, and species.
  • Alpha Proteobacteria
    • Contains obligate and facultative pathogens, including rickettsias; some can convert nitrogen to usable forms.
  • Beta Proteobacteria
    • Includes diverse bacteria, such as human pathogens Treponema and Neonseria.
  • Gamma Proteobacteria
    • The largest and most diverse group; many species are human pathogens, including Escherichia coli.
  • Delta Proteobacteria
    • Small group known to reduce sulfate or sulfur, including scavengers forming myxospores.
  • Epsilon Proteobacteria
    • The smallest group with known human pathogens like Campylobacter and Helicobacter.

4.3 Nonproteobacteria Gram-Negative Bacteria and Phototrophic Bacteria

  • Classification
    • Includes taxa such as spirochetes, chlamydia, fusobacterium, and planctomycetes.
  • Spirochetes
    • Motile, spiral bacteria; some are human pathogens causing diseases like syphilis and Lyme disease.
  • CFB Group
    • Cytophaga, Fusobacterium, and Bacteroides, known for their anaerobic, rod-shaped characteristics.
  • Planctomycetes
    • Aquatic bacteria that reproduce by budding.
  • Phototrophic Bacteria
    • Group using sunlight for energy; includes sulfur and nonsulfur bacteria.
    • Cyanobacteria, known for oxygen production and significant contributions to early atmospheric conditions.

4.4 Gram-Positive Bacteria

  • Classification
    • Divided into high G+C and low G+C gram-positive bacteria based on the guanine and cytosine nucleotide ratios.
  • Actinobacteria
    • Class of high G+C gram-positive; includes many genera like Mycobacterium and Corynebacterium with medical significance.
  • Pathogenic Examples
    • Mycobacterium tuberculosis (tuberculosis), M. leprae (leprosy), Corynebacterium diphtheriae (diphtheria).
  • Clostridia
    • Low G+C obligate anaerobes forming endospores; pathogens include C. perfringens (gas gangrene) and C. tetani (tetanus).
  • Lactobacillales
    • Include genera responsible for diseases like Streptococcus spp. causing throat infections and other complications.
  • Bacilli
    • Low G+C class comprising rod-shaped and coccus-shaped species, including Staphylococcus, associated with a range of infections.
  • Mycoplasma
    • Lack cell walls; M. pneumoniae causes atypical pneumonia.

4.5 Deeply Branching Bacteria

  • Definition
    • Most ancient forms of life, closest to universal common ancestor.
  • Environmental Adaptation
    • Thrive in extreme conditions resembling early Earth.

4.6 Archaea

  • Definition
    • Unicellular, prokaryotic microorganisms distinct from bacteria in genetics and biochemistry.
  • Extremophiles
    • Some archaea live in extreme temperatures or salinity.
  • Methanogens
    • Archaea known for producing methane.
  • Lack of Pathogenicity
    • Archaea generally not associated with human disease.

5.1 Unicellular Eukaryotic Parasites

  • Definition of Protists
    • Diverse, polyphyletic group of eukaryotic organisms.
  • Characteristics
    • Include unicellular or multicellular forms; vary in nutrition, morphology, locomotion, and reproduction.
  • Structures
    • Include contractile vacuoles, cilia, flagella, pellicles, pseodopodia.
  • Pathogenicity
    • Some protists are significant pathogens.

5.2 Parasitic Helminths

  • Helminths in Microbiology
    • Identified by microscopic eggs and larvae.
  • Major Groups
    • Roundworms (Nematoda) and flatworms (Platyhelminthes).
  • Common Nematodes
    • Common intestinal parasites transmitted through undercooked foods.
  • Flatworm Classification
    • Includes tapeworms and flukes, typically transmitted via undercooked meat.

5.3 Fungi

  • Definition
    • Diverse saprotrophic eukaryotic organisms with chitin cell walls.
  • Forms
    • Unicellular or multicellular; can vary in size.
  • Medically Important Groups
    • Zygomycota, Ascomycota, Basidiomycota, Microsporidia.
  • Toxicity
    • Many produce deadly toxins.
  • Drug Targets
    • Differences like ergosterols make fungal cells targets for antifungal medications.

5.4 Algae

  • Definition
    • Photosynthetic eukaryotic protists, may be unicellular or multicellular.
  • Seaweeds
    • Large multicellular algae not classified as plants.
  • Pathogenic Associations
    • Generally non-pathogenic but associated with toxic algal blooms.

5.5 Lichens

  • Definition
    • Symbiotic associations between fungi and algae or cyanobacteria.
  • Nature of Symbiosis
    • Considered controlled parasitism.
  • Ecological Significance
    • Help create soil, provide food, and indicate air quality through sensitivity to pollutants.