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Questions and Answers
What is the primary function of ribosomes in bacterial cells?
What is the primary function of ribosomes in bacterial cells?
Which of the following statements about bacterial spores is true?
Which of the following statements about bacterial spores is true?
Which type of antibiotic primarily inhibits cell wall synthesis?
Which type of antibiotic primarily inhibits cell wall synthesis?
What defines bactericidal antibiotics?
What defines bactericidal antibiotics?
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What is a characteristic of the process of sporulation in bacteria?
What is a characteristic of the process of sporulation in bacteria?
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What is the primary function of flagella in bacteria?
What is the primary function of flagella in bacteria?
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Which structural component is part of the cell envelope of a bacterium?
Which structural component is part of the cell envelope of a bacterium?
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Which type of bacteria typically possesses sex pili?
Which type of bacteria typically possesses sex pili?
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What distinguishes axial filaments from other types of bacterial appendages?
What distinguishes axial filaments from other types of bacterial appendages?
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Where are common pili found?
Where are common pili found?
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What is the composition of a bacterial capsule primarily made of?
What is the composition of a bacterial capsule primarily made of?
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Which of the following bacteria is known for having flagella as a means of motility?
Which of the following bacteria is known for having flagella as a means of motility?
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What is the primary purpose of the capsule in bacteria like Bacillus anthracis?
What is the primary purpose of the capsule in bacteria like Bacillus anthracis?
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What components make up the peptidoglycan backbone in bacterial cell walls?
What components make up the peptidoglycan backbone in bacterial cell walls?
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How does the cell wall of Gram-positive bacteria differ from that of Gram-negative bacteria?
How does the cell wall of Gram-positive bacteria differ from that of Gram-negative bacteria?
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Which structure is responsible for cross-linking peptidoglycan chains in bacterial cell walls?
Which structure is responsible for cross-linking peptidoglycan chains in bacterial cell walls?
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What is one of the functions of the cytoplasmic membrane?
What is one of the functions of the cytoplasmic membrane?
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What is a characteristic feature of Gram-negative bacteria's outer membrane?
What is a characteristic feature of Gram-negative bacteria's outer membrane?
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Which type of bacteria typically have mesosomes and what is their function?
Which type of bacteria typically have mesosomes and what is their function?
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What role do plasmids play in bacteria?
What role do plasmids play in bacteria?
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What is the significance of using a capsule stain in clinical settings?
What is the significance of using a capsule stain in clinical settings?
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Which of the following statements about the cytoplasm in bacteria is correct?
Which of the following statements about the cytoplasm in bacteria is correct?
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Study Notes
Bacterial Cell Structure
- Bacterial cells have three main components: appendages, envelopes, and cytoplasmic contents.
- Appendages include flagella, fimbriae/pili, and axial filaments (endoflagella).
- The cell envelope consists of the capsule, cell wall, and cytoplasmic membrane, layers from outside to inside.
- Cytoplasmic contents include nucleic acid, plasmids, and ribosomes.
Cell Appendages (Flagella, Fimbriae, Axial Filaments)
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Flagella:
- Originate in cytoplasm
- Long, thick, and twisted protein structures
- Present in Gram-positive and Gram-negative bacteria.
- Function in motility
- Different arrangements include monotrichous (one flagellum), lophotrichous (multiple flagella at one end) , amphitrichous (flagella at both ends) and peritrichous (flagella diffused over the entire surface).
- Examples of bacteria with flagella are Salmonella, Vibrio cholerae, and E. coli.
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Fimbriae/Pili:
- Originate in cytoplasmic membrane
- Short, thin protein structures.
- Present in all Gram-negative bacteria and some Gram-positive bacteria.
- Numerous per bacterial cell.
- Function in adhesion to surface.
- Adhere to host cells and other bacteria
- Sex pili involve in gene transfer by conjugation.
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Axial Filaments/Endoflagella:
- Located in periplasmic space
- Present in spirochetes (such as Treponema)
- Run along the axis of the bacteria, enabling rotation and motility.
Cell Envelope (Capsule, Cell Wall, Cytoplasmic Membrane)
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Capsule:
- Outermost layer, sometimes formed in vivo.
- Present in most pathogenic bacteria.
- Composition can be polysaccharides (e.g., Streptococcus pneumoniae) or polypeptides (e.g., Bacillus anthracis).
- Demonstrated via capsule stain or India ink wet mount techniques.
- Importance in virulence as it aids in preventing phagocytosis and serving as a protective barrier from the host’s immune cells.
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Cell Wall:
- Lies outside the cytoplasmic membrane.
- Shape determinant.
- Structure: Peptidoglycan backbone composed of alternating sugars (N-acetylglucosamine and N-acetylmuramic acid) and peptides.
- Gram positive bacteria have a thick peptidoglycan layer.
- Gram negative bacteria have a thin peptidoglycan layer covered by an outer membrane.
- Gram negative outer membrane: Lipopolysaccharide (LPS) and Lipid A.
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Cytoplasmic Membrane:
- Consists of phospholipid bilayers and proteins.
- Functions include selective permeability, transport of solutes, energy production(electron transport chain), excretion of hydrolytic exoenzymes and toxic wastes, and cell wall biosynthesis.
- Mesosomes are invaginations found in some bacteria that increase membrane surface area and play a role in cell division.
Cytoplasmic Contents (Chromosome, Plasmid, Ribosomes)
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Chromosome:
- Single, double-stranded DNA (helix).
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Plasmid:
- Extra circular double stranded DNA segment.
- Found in some bacteria.
- Capable of autonomous replication.
- Function: carrying genes for antibiotic resistance.
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Ribosomes:
- Composed of rRNA and proteins.(70s: 50s and 30s subunits)
- Function: protein synthesis.
Bacterial Spores
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Spores:
- Resistant structures formed under adverse environmental conditions (chemicals, radiation, freezing, and heat).
- Remain viable for extended periods.
- Formed by some bacteria, including Bacillus and Clostridium.
- Sporulation: Process forming inactive spore from active vegetative cells.
- Spores contain DNA enclosed in a multi-layered, rigid envelope.
- Envelope is strengthened by keratin and calcium dipicolinate.
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Spore Germination:
- Spores germinate in suitable conditions.
- Spore coat destruction creates active vegetative bacterial cells.
- Germinated spore divides by binary fission.
Antimicrobial Chemotherapy
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Antimicrobials:
- Chemicals that kill or inhibit the growth of microorganisms (bacteria, fungi, viruses, and parasites).
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Classification:
- Source (natural, synthetic, or semisynthetic).
- Action (bactericidal, bacteriostatic).
- Spectrum (broad or narrow).
- Bactericidal antibiotics kill the bacteria.
- Bacteriostatic antibiotics inhibit bacterial growth.
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Target Sites for Antibiotics:
- Cell wall synthesis
- Cell membrane
- Protein synthesis
- Nucleic acid synthesis
- Examples of antibiotics targeting specific sites are Penicillins, Cephalosporins, Glycopeptides(Vancomycin), Polymyxins, Macrolides (erythromycin, azithromycin), Aminoglycosides (gentamicin), Tetracyclines, Fluoroquinolones, Sulfonamides, and Rifampicin.
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Description
Test your knowledge on the components of bacterial cells, including appendages, envelopes, and cytoplasmic contents. This quiz covers details about flagella, fimbriae, and structural organization in bacteria. Challenge yourself to identify key features and functions of these microorganisms.
