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Questions and Answers
What is the function of the mesosome during cell division?
What is the function of the mesosome during cell division?
Which component of the cytoplasm contains the genetic material in prokaryotic cells?
Which component of the cytoplasm contains the genetic material in prokaryotic cells?
What distinguishes bacterial ribosomes from eukaryotic ribosomes?
What distinguishes bacterial ribosomes from eukaryotic ribosomes?
What is a primary characteristic of bacterial DNA compared to eukaryotic DNA?
What is a primary characteristic of bacterial DNA compared to eukaryotic DNA?
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What role do plasmids play in bacterial cells?
What role do plasmids play in bacterial cells?
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What type of granules are found in the cytoplasm of prokaryotic cells?
What type of granules are found in the cytoplasm of prokaryotic cells?
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Why is the selective action of certain antibiotics significant?
Why is the selective action of certain antibiotics significant?
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Which of the following is NOT a characteristic of the nucleoid in prokaryotic cells?
Which of the following is NOT a characteristic of the nucleoid in prokaryotic cells?
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What is the component of LPS that is primarily responsible for its toxic effects?
What is the component of LPS that is primarily responsible for its toxic effects?
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What characterizes the outer polysaccharide of LPS in gram-negative bacteria?
What characterizes the outer polysaccharide of LPS in gram-negative bacteria?
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Why are mycobacteria described as acid-fast?
Why are mycobacteria described as acid-fast?
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Which function is NOT associated with the cytoplasmic membrane of prokaryotic cells?
Which function is NOT associated with the cytoplasmic membrane of prokaryotic cells?
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What is a characteristic feature of cell wall-deficient (CWD) bacteria?
What is a characteristic feature of cell wall-deficient (CWD) bacteria?
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What distinguishes eukaryotic membranes from prokaryotic membranes?
What distinguishes eukaryotic membranes from prokaryotic membranes?
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What is the role of porin proteins in the outer membrane of gram-negative bacteria?
What is the role of porin proteins in the outer membrane of gram-negative bacteria?
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Which of the following statements about mycolic acids is true?
Which of the following statements about mycolic acids is true?
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What is the primary action of beta-lactam antibiotics on penicillin binding proteins (PBPs)?
What is the primary action of beta-lactam antibiotics on penicillin binding proteins (PBPs)?
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Which of the following best describes teichoic acids?
Which of the following best describes teichoic acids?
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What role do lipopolysaccharides (LPS) play in gram-negative bacteria?
What role do lipopolysaccharides (LPS) play in gram-negative bacteria?
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Which statement accurately describes the binding action of penicillin within bacterial cell walls?
Which statement accurately describes the binding action of penicillin within bacterial cell walls?
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What significant effect do teichoic acids have on gram-positive bacteria?
What significant effect do teichoic acids have on gram-positive bacteria?
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How does the structure of the gram-negative cell wall differ from that of gram-positive bacteria?
How does the structure of the gram-negative cell wall differ from that of gram-positive bacteria?
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What distinguishes endotoxins from exotoxins in bacterial cells?
What distinguishes endotoxins from exotoxins in bacterial cells?
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What is the significance of penicillin's structural similarity to D-alanine?
What is the significance of penicillin's structural similarity to D-alanine?
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What is the primary function of transmissible plasmids?
What is the primary function of transmissible plasmids?
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How do non-transmissible plasmids primarily differ from transmissible plasmids?
How do non-transmissible plasmids primarily differ from transmissible plasmids?
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What type of enzymes do plasmids code for to assist in resistance to heavy metals?
What type of enzymes do plasmids code for to assist in resistance to heavy metals?
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Which statement correctly describes transposons?
Which statement correctly describes transposons?
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What role do pili (fimbriae) play in bacterial interaction with the body?
What role do pili (fimbriae) play in bacterial interaction with the body?
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What is the molecular weight range of non-transmissible plasmids?
What is the molecular weight range of non-transmissible plasmids?
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What function is NOT associated with plasmids?
What function is NOT associated with plasmids?
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Which of the following is NOT a specialized structure found outside the cell wall of bacteria?
Which of the following is NOT a specialized structure found outside the cell wall of bacteria?
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What distinguishes the different serologic types of Streptococcus pneumoniae?
What distinguishes the different serologic types of Streptococcus pneumoniae?
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What role does the capsule play in bacteria's interaction with the immune system?
What role does the capsule play in bacteria's interaction with the immune system?
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Which of the following correctly describes flagella?
Which of the following correctly describes flagella?
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What happens when a bacterial capsule is exposed to a homologous antibody?
What happens when a bacterial capsule is exposed to a homologous antibody?
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Which type of bacteria are primarily associated with urinary tract infections due to their flagella?
Which type of bacteria are primarily associated with urinary tract infections due to their flagella?
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What type of structure do spirochetes use to facilitate movement?
What type of structure do spirochetes use to facilitate movement?
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What is one function of capsular polysaccharides in vaccines?
What is one function of capsular polysaccharides in vaccines?
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Which statement about flagella is true?
Which statement about flagella is true?
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What is the primary role of pili in bacteria?
What is the primary role of pili in bacteria?
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Which of the following genera of bacteria is known for producing highly resistant spores?
Which of the following genera of bacteria is known for producing highly resistant spores?
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What type of pilus is specifically involved in bacterial conjugation?
What type of pilus is specifically involved in bacterial conjugation?
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What structure allows bacteria to adhere firmly to surfaces like heart valves and skin?
What structure allows bacteria to adhere firmly to surfaces like heart valves and skin?
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Which condition primarily triggers spore formation in certain bacteria?
Which condition primarily triggers spore formation in certain bacteria?
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Which of the following is NOT a component of bacterial spores?
Which of the following is NOT a component of bacterial spores?
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What is the primary function of the glycocalyx in bacteria such as Streptococcus mutans?
What is the primary function of the glycocalyx in bacteria such as Streptococcus mutans?
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What distinguishes pili and flagella in bacterial structure?
What distinguishes pili and flagella in bacterial structure?
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Study Notes
Bacterial Structure
- Bacteria are classified into three basic groups: cocci (round), bacilli (rods), and spirochetes (spiral).
- Some bacteria are pleomorphic, meaning they have variable shapes.
- Bacterial morphology includes cocci in clusters, chains, pairs, or various shapes.
- Rods demonstrate square ends, round ends, club-shaped, fusiform, or comma shapes.
- Spirochetes can be tightly coiled or relaxed.
Learning Objectives
- Students should be able to define typical bacteria.
- Bacterial morphology (appearance).
- Cell wall structure (peptidoglycans).
- Cell wall variations in gram-positive and gram-negative bacteria.
- Cell membrane, mesosomes, ribosomes, and genetic material.
- Specialized structures outside the cell wall (capsule, pili, flagella, glycocalyx).
Structure of Bacterial Cells
- Bacteria are classified by shape into cocci, bacilli, and spirochetes.
- Cocci are round, bacilli are rod-shaped, and spirochetes are spiral-shaped.
- Some bacteria are variable in shape and are called pleomorphic.
Bacterial Morphology
-
Cocci:
- Clusters (e.g., Staphylococcus).
- Chains (e.g., Streptococcus).
- Pairs (e.g., Streptococcus pneumoniae; Neisseria).
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Rods (bacilli):
- Square ends (e.g., Bacillus).
- Rounded ends (e.g., Salmonella).
- Club-shaped (e.g., Corynebacterium).
- Fusiform (e.g., Fusobacterium).
- Comma-shaped (e.g., Vibrio).
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Spirochetes:
- Relaxed coil (e.g., Borrelia).
- Tightly coiled (e.g., Treponema).
Essential Cell Structures
-
Cell wall: The outermost layer (except in Mycoplasma).
- Composed of peptidoglycan and an outer membrane.
- Varying thickness and chemical composition between bacterial types.
- Provides structural support and maintains cell shape.
- Protects against osmotic pressure.
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Peptidoglycan: Also called murein or mucopeptide.
- Found only in bacterial cell walls.
- Provides rigid support to the cell.
- Maintains cell shape.
- Site of action of penicillin and related antibiotics.
- Composed of glycan chains connected by peptide bonds.
- Repeating sugars NAG and NAM in the glycans.
- The glycan chains, connected by peptide bonds, are the target for lysozyme.
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Gram-positive and Gram-negative walls:
- Gram-positive cells have a thick peptidoglycan layer (50%–80% of dry weight); gram-negative cells have a thin peptidoglycan layer (5%–10% of dry weight).
-
Cytoplasmic membrane: Located inside the peptidoglycan.
- Similar to eukaryotic membranes, but without sterols - except in Mycoplasma.
- Contains phospholipids and transmembrane proteins.
- Involved in molecule transport, energy generation, and secretion of enzymes and toxins
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Mesosome: Invagination of the cytoplasmic membrane.
- Important in cell division
- Site of DNA replication.
-
Cytoplasm: The interior of the cell.
- Contains ribosomes, nutrient granules, metabolites, and plasmids, which are in an amorphous matrix.
Ribosomes
- Bacterial ribosomes are 70S (50S and 30S subunits). Eukaryotic ribosomes are 80S (60S and 40S subunits).
Granules
- Cytoplasm contains granules that function in nutrient storage.
- The granules stain uniquely with certain dyes.
Nucleoid
- The nucleoid is the area of the cytoplasm where DNA is located.
- Prokaryotic DNA is a single, circular molecule.
- Bacterial DNA lacks a nuclear membrane, nucleolus, mitotic spindle, and histones.
- Bacterial DNA contains no introns, which differs from eukaryotic DNA.
Plasmids
- Plasmids are extrachromosomal, double-stranded, circular DNA molecules.
- They replicate independently of the bacterial chromosome.
- Some plasmids are transmissible (e.g., conjugation).
- Some are non-transmissible.
- Carry important genes, for example antibiotic resistance.
Specialized Structures
-
Capsule:
- Gelatinous layer covering the entire cell (except anthrax, which has a protein capsule).
- Composed of polysaccharide (except in anthrax bacillus).
- Sugar components vary between bacterial species; these variations are used in bacterial identification.
- The capsule can protect bacteria from phagocytosis.
-
Flagella:
- Long, whip-like appendages involved in chemotaxis.
- Location and number vary between species.
- Useful in bacterial identification (H antigens).
-
Pili (fimbriae):
- Hairlike filaments.
- Shorter and straighter than flagella.
- Primarily found in gram-negative bacteria.
- Essential in bacterial attachment to surfaces and conjugation.
-
Glycocalyx (slime layer):
- Polysaccharide coating.
- Allows bacteria to attach firmly to surfaces.
- Mediates adherence to surfaces
- Plays a role in biofilm formation.
Spores
- Highly resistant structures forming in adverse conditions in certain genera. -e.g., Bacillus and Clostridium species
- Enable survival during harsh conditions.
- Thick, protective coat.
Teichoic Acid
- Found only in gram-positive bacteria.
- Involved in pathogenicity (induces septic shock).
- Site of attachment to mucosal surfaces.
Porins
- Protein structures in gram-negative bacteria cell walls.
- Form channels, allowing the passage of various substances.
- Phage receptors.
Acid-Fast and Associated Cell Wall
- Example genera include Mycobacteria and Nocardia.
- Rich in lipid, especially mycolic acids.
- Cell wall structure resists Gram staining.
- Resist decolorization with acid-alcohol; that is, they are "acid-fast."
L-form Bacteria
- Strains lack a cell wall.
- Can survive exposure to lysozyme or antibiotics.
Lipopolysaccharide (LPS)
- Part of the outer membrane of gram-negative bacteria.
- Endotoxin
- Responsible for several symptoms of disease.
Exotoxin
- Secreted by bacteria.
- Causes various effects and diseases.
Important Note
- Differences between prokaryotic and eukaryotic ribosomes are important for the development of antibiotics.
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