Microbiology Basics Quiz

Microbiology and Microorganisms

• Microbiology is the science of microorganisms (micros = small, bios = life, logos = science).
• Microorganisms are small living organisms that are not visible to the naked eye, but can be seen using a microscope.
• Examples include bacteria, viruses, and fungi

Eukaryotes and Prokaryotes

• Prokaryotes (pro = premature or primitive, karyon = nucleus):
  • Cells with a premature nucleus (single, naked chromosome without nuclear membrane).
  • Examples include bacteria and rickettsia.
• Eukaryotes (eu = true, karyon = nucleus):
  • Cells with a true nucleus containing a nuclear membrane, nucleolus, and multiple chromosomes.
  • Examples include fungi.

Bacterial Cell Structure

• Essential Structures (found in all bacteria):
  • Cell wall
  • Cytoplasmic membrane
  • Cytoplasm
  • Nuclear body
• Additional Structures (found in some, not all bacteria):
  • Capsule
  • Flagella
  • Fimbriae (pili)
  • Inclusion granules

Cell Wall

• The outer covering layer of the bacterial cell (outside the cytoplasmic membrane).
• Basic Layer (Peptidoglycan):
  • Composed of carbohydrate and protein.
  • Carbohydrate backbone: N-acetyl glucosamine and N-acetyl muramic acid.
  • Protein part: tetrapeptide side chains.
  • Responsible for the rigidity of the cell wall. Forms 80% of Gram-positive bacterial cell walls and 20% of Gram-negative bacterial cell walls.
• Additional Layer:
  • Gram-positive bacteria: teichoic acid.
  • Gram-negative bacteria: lipopolysaccharides (with a lipid A component, a core polysaccharide and an outer polysaccharide), and lipoproteins..
• Periplasmic Space: The space between the inner and outer membranes containing peptidoglycan and enzymes like β-lactamase.

Cytoplasmic Membrane

• Semipermeable, double-layered membrane (just inside the cell wall and surrounding the cytoplasm).
• Composition: Primarily lipoprotein (70% protein, 30% phospholipids).
• Functions:
  • Selective permeability: transport of nutrients into the cell and waste products out.
  • Active transport of ions and molecules.
  • Contains respiratory enzymes and pigments for oxidative phosphorylation to produce energy.
  • Role in DNA replication and cell wall synthesis.
  • Excretion of some proteins (e.g. IgA protease).
• Mesosomes: Invaginations of the cytoplasmic membrane within the cell cytoplasm. Common in Gram-positive bacteria.

Cytoplasm

• Homogeneous, soft gel-like substance within the bacterial cell.
• Contents include:
  • Nuclear body (DNA)
  • Ribosomes
  • Storage granules (inclusions)
  • Enzymes.
  • Plasmids (extrachromosomal DNA)

Ribosomes

• Complex, minute structures within the cytoplasm.
• Composed of RNA (60%) and proteins (40%).
• Bacterial ribosomes (70S) have two subunits (50S and 30S).
• Function in protein synthesis.

The Nuclear Body

• Mass of DNA, forming a single chromosome (double-stranded DNA molecule).
• Contains the cell's genetic information.
• Duplicates before cell division—no nuclear membrane or nucleolus.

Plasmids

• Extrachromosomal, double-stranded, circular DNA that replicates independently of the bacterial chromosome.

Capsules

• Gelatinous layer outside the cell wall, mostly composed of polysaccharides.
• Functions:
  • Virulence factor (prevents phagocytosis).
  • Protection from bacteriophages, complements, and lysozymes.
  • Important for bacterial identification and typing (e.g. pneumococcus).
  • Adherence to tissues.

Flagella

• Long, hollow, filamentous appendages used for motility.
• Structure: composed of flagellin protein.
• Function: Responsible for bacterial motility.

Fimbriae (Pili)

• Short, hair-like filaments mainly found on Gram-negative bacteria.
• Structure: composed of pilin protein.
• Function: Adherence to surfaces and transfer of genetic material (conjugation).

Spores

• Highly resistant, resting forms of certain bacteria.
• Formed in response to unfavorable conditions (e.g., dryness, lack of nutrients).
• Sporulation (sporogenesis) is the process of spore formation.
• Germination is the process of vegetative cells forming from spores.
• Medical importance:
  • Resistance to heat and chemicals. Useful for identification of bacteria (e.g., Clostridium tetani spores).

Glycocalyx (Slime Layer)

• Thin coat of polysaccharide that covers the bacterial surface.
• Composition: Polysaccharide.
• Function: Facilitates bacterial adhesion and colonization.