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Questions and Answers
What role does the slime layer play for bacteria?
Which component is primarily responsible for bacterial motility?
What are extracellular polymeric substances (EPS) primarily involved in?
Which step is NOT part of biofilm formation?
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Which structure connects the flagellum to the bacterial cell body?
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What role do pili primarily play in bacterial infections?
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Which of the following correctly describes twitching motility?
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What is the function of the sex pilus in bacteria?
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Which of the following statements is true about the fimbriae of Streptococcus?
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What characterizes the common pili found in many bacteria?
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What is the primary function of ribosomes in the cytoplasm?
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Which of the following accurately describes plasmids?
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What type of genetic material is primarily found in the nucleoid of a bacterial cell?
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Which of the following statements about inclusion bodies is correct?
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Which type of plasmid is responsible for producing β-lactamase?
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What type of granular structure is glycogen classified as?
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Which of the following best describes the structure of ribosomes?
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What is the primary role of organic and inorganic ions in the cytoplasm?
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What is the primary function of the spore coat in bacterial spores?
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What distinguishes the cortex of a bacterial spore from the normal peptidoglycan layer?
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Which layer provides an organized structure that protects bacteria from phagocytosis?
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How does the structure of the glycalyx assist bacteria in surviving in their environment?
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What is a key characteristic of the slime layer compared to a capsule?
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Which type of bacterial capsule is unique due to its composition?
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What role does the exosporium play in bacterial spores?
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What is one of the main protective functions of the glycalyx in bacteria?
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What is the primary function of fimbriae in gram-negative bacteria?
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Which arrangement of flagella describes a bacterium with a single flagellum at one end?
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How do spirochetes primarily move?
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What effect does a 'tumble' have on bacterial movement?
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What structure is formed by the intertwining chains of flagellin in the filaments?
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Which characteristic does NOT describe axial filaments?
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What defines an 'atrichous' bacterium?
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Which bacterium is known for having fimbriae involved in disease processes?
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Study Notes
Internal Cell Structures
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The cytoplasm is an aqueous solution containing macromolecules (proteins, mRNA, tRNA), small molecules (energy sources, metabolites, vitamins), and inorganic ions.
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The nucleoid is the bacterial DNA, a single circular chromosome without a nuclear membrane or mitotic apparatus.
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Ribosomes are responsible for protein synthesis, composed of RNA and proteins.
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Ribosomes are 70S in size, composed of 30S & 50S subunits.
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Found either in the matrix or on the plasma membrane (PM).
Plasmids
- Extrachromosomal, double-stranded DNA elements associated with virulence.
- Located in the cytoplasm, they code for antibiotic resistance and toxin production.
- Not essential for bacterial growth, but can be crucial for survival in certain environments.
- Two types: large plasmids (produce β-lactamase for β-lactam antibiotic resistance) and small plasmids (resistance to tetracyclines and chloramphenicol).
Inclusion Bodies
- Function as energy sources, food reserves, or structural building blocks.
- Composed of polysaccharides, reducing osmotic pressure.
- Examples include glycogen, cyanophysin granules, poly-β-hydroxybutyrate granules, carboxysomes, gas vacuoles, and polyphosphate granules.
Spores
- Spore wall/ core wall: the innermost layer surrounding the inner spore membrane; contains normal peptidoglycan.
- Cortex: the thickest layer, with a unique type of peptidoglycan containing fewer cross-links.
- Spore coat: composed of keratin-like protein with disulfide bonds, contributing to the spore's resistance.
- Exosporium: comprised of proteins, lipids, and carbohydrates; consists of a basal layer and a hair-like outer region. Examples: Bacillus anthracis and B.cereus.
External Cell Structures
- Glycocalyx: a polysaccharide complex on the bacterial surface that aids in attachment.
- Functions:
- Protection against ion and pH changes, osmotic stress, enzymes, predacious bacteria, and phagocytes.
- Enhances the virulence of pathogenic bacteria.
Capsules
- Well-organized, firmly attached to the cell wall.
- Located outside the murein layer in gram-positive bacteria and the outer membrane in gram-negative bacteria.
- Composed of polysaccharide polymers, except in Bacillus anthracis and Bacillus licheniformis (poly-D-glutamic acid capsules).
- Provides protection against the host's defense system by resisting phagocytosis and desiccation.
- Capsule removal is necessary for detection of somatic antigens.
Slime Layer
- Unorganized, loosely attached to the cell wall.
- Composed of polysaccharide.
- Can inhibit phagocytosis or aid in bacterial adherence to host tissues or implants.
- Facilitates bacterial colonization of surfaces and biofilm formation.
Extracellular Polymeric Substance (EPS)
- Mediates attachment of cells within a biofilm to their environment and to each other.
- Protects cells, facilitates communication, and enhances survival in the environment.
Biofilm Formation
- Steps:
- Attachment
- Growth
- Detachment
Flagella
- Protein filaments that rotate, enabling bacterial motility.
- Complex structures primarily composed of flagellin.
- Thread-like appendages with a diameter of 12-30nm.
- Essential for survival and disease causation.
- Antigenic (H antigens).
- Some bacteria exhibit gliding motility (e.g., Capnocytophaga, Cyanobacteria, Myxobacteria).
Flagellar Components
- Hook: a short, curved structure acting as a universal joint.
- Basal body: contains rings (one pair in gram-positive bacteria and two pairs in gram-negative bacteria).
- Filament: the long, outermost region, containing flagellin arranged in helical chains.
Motility
- "Run" or "Swim": bacterium moves in one direction for an extended period.
- "Tumbles": sudden, random changes in direction caused by flagellar rotation reversal.
Flagellar Arrangement
- Atrichous: without flagella.
- Monotrichous: single flagellum at one end.
- Amphitrichous: single flagellum at both ends.
- Lophotrichous: a tuft or group of flagella on one end or both ends.
- Peritrichous: flagella covering the entire cell surface.
Axial Filaments
- Bundles of fibrils spiraling around the cell, extending from the ends beneath an outer sheath.
- Anchored at one end of the spirochete.
- Similar structure to flagella.
- Rotation of filaments propels spirochetes in a spiral motion.
- Found in spirochetes.
Fimbriae
- Short, fine, hair-like appendages in gram-negative bacteria.
- Not involved in motility.
- Aid in bacterial attachment to solid surfaces.
- Contribute to the formation of pellicles (thin sheets of cells on liquid surfaces) and biofilms.
- Involved in bacterial pathogenesis.
Pili
- Long, hair-like proteinaceous structures extending from the cell membrane.
- Serve as adhesins, facilitating bacterial attachment to host cell surfaces.
- Composed of pilin subunits.
Twitching Motility
- Pili extend and retract, causing short, jerky movements.
- Enabled by the addition and disassembly of pilin subunits.
- Examples: Pseudomonas aeruginosa, Neisseria gonorrhoeae, E. coli.
Common Pili
- Play a role in bacterial adherence to surfaces, contributing to virulence.
Sex Pilus
- Conduit for DNA transfer during conjugation.
- Present only in cells possessing the F factor.
- F-positive cells initiate conjugation with F-negative cells.
Streptococci
- Fimbriae function as the main surface antigen (M protein).
- Lipoteichoic acid, associated with fimbriae, aids in adherence to epithelial cells.
N. gonorrhoeae
- Able to produce pili of different antigenic types (antigenic variation).
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Description
This quiz covers the internal structures of bacterial cells, including the cytoplasm, nucleoid, ribosomes, and plasmids. It also explores the significance of inclusion bodies and antibiotic resistance mechanisms in bacteria. Test your knowledge of these fundamental concepts in microbiology!
