Bacteria Characteristics Quiz

Bacterial Structure and Function

• Bacteria are prokaryotic cells, lacking a nucleus and membrane-bound organelles.
• Eukaryotic cells, in contrast, have a nucleus and membrane-bound organelles like the Golgi apparatus, endoplasmic reticulum, and mitochondria.
• Prokaryotes reproduce through binary fission.
• Eukaryotes reproduce via mitosis.
• Most bacteria are monomorphic (one shape), but some are pleomorphic (multiple shapes).
• Bacteria come in various shapes: cocci (spherical), bacilli (rod-shaped), and spirals (curved or helical).
• Specific examples of bacteria and their shapes include:
  • Streptococcus pyogenes (cocci)
  • Streptococcus pneumoniae (diplococci)
  • Bacillus anthracis (bacilli)
  • Vibrio cholerae (vibrio)
  • Helicobacter pylori (spiral)
  • Salmonella typhi (flagellate rods)
  • Clostridium botulinum (spore former).
  • Treponema pallidum (spirochetes),

Bacterial External Structures

• Glycocalyx: An external layer to the cell wall, made of polysaccharides and/or polypeptides,
  • Capsule: neatly organized and firmly attached (often larger than the cell), aiding in attachment and preventing phagocytosis.
  • Slime layer: unorganized and easily washed away, assisting in attachment
• Flagella: Filamentous appendages used for motility in aqueous environments, made of the protein flagellin.
  • Three parts: filament, hook, and basal body.
• Polar Arrangements:
  • Monotrichous: a single flagellum at one end
• Polar Arrangements:
  • Amphitrichous: a flagellum at each end
  • Lophotrichous: multiple flagella at one or both ends
  • Peritrichous: flagella distributed around the entire cell.
• Motility:
  • Flagella rotate and cause a "run" or "tumble" motion, allowing bacteria to move towards or away from stimuli (chemotaxis or phototaxis), in response to a chemical.
• Axial filaments (endoflagella): Found in spirochetes, these internal structures allow for corkscrew-type movement.

Bacterial Internal Structures

• Fimbriae Hair- or brush-like structures that aid in attachment.
• Pili: Often involved in motility (gliding and twitching) and DNA transfer (conjugation).

Bacterial Cell Wall

• The cell wall prevents osmotic lysis and protects the cell membrane.
• The bacterial cell wall is composed of peptidoglycan, a polymer of N-acetylglucosamine (NAG) and N-acetylmuramic acid (NAM) subunits.
• Gram-positive: Thick peptidoglycan layer.
  • Lipoteichoic acid links peptidoglycan to plasma membrane.
  • Wall teichoic acid links the peptidoglycan layers.
• Gram-negative: Thin peptidoglycan layer.
  • Contains lipopolysaccharides (LPS).
  • LPS contains lipid A (an endotoxin).
  • Outer membrane lies outside the peptidoglycan
  • Periplasmic space is between the peptidoglycan layer and the outer membrane.
• Porins are proteins that form channels within the outer membrane for passage of molecules.
• The Gram stain distinguishes Gram-positive (purple) and Gram-negative (pink) bacteria based on their cell wall structure.

Bacterial Plasma Membrane

• A phospholipid bilayer that encloses the cytoplasm, composed of a phospholipid bilayer with embedded proteins.
• Peripheral proteins attach to the membrane surface, while integral proteins span the membrane.

Cytoplasm

• Cytoplasm is the substance within the plasma membrane, mainly composed of water.
• It houses genetic material (chromosome, plasmids), ribosomes, granules, and cytoskeleton.

Bacterial Genetic Information

• Bacterial chromosome is a circular DNA strand found in the nucleoid region.
• Plasmids are circular, extrachromosomal DNA that carry genes not directly related to survival.

Bacterial Ribosomes

• Ribosomes are the sites of protein synthesis in bacteria.
• Bacterial ribosomes are 70S, composed of 50S and 30S subunits.
• Eukaryotic ribosomes are 80S (made of 60S and 40S subunits.)

Bacterial Inclusions (Storage Bodies)

•  Metachromatic granules (volutin), polysaccaride granules, lipid granules, sulfur granules are storage bodies used for energy or other functions.
• Carboxysomes contain RuBisCO enzyme, important for CO2 fixation (photosynthesis).
• Gas vacuoles maintain buoyancy for bacteria.

Bacterial Endospores

• Endospores are resting, dormant cells created when conditions become stressful or nutrients are scarce.
• Endospores are highly resistant to heat, chemicals, desiccation, and radiation.
• Bacterial genera like Bacillus and Clostridium produce endospores.
• Steps of endospore formation (sporulation) are diagrammed.