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Questions and Answers
What is one function of the bacterial cell wall?
What is one function of the bacterial cell wall?
Which component is NOT found in prokaryotic cells?
Which component is NOT found in prokaryotic cells?
What happens to bacteria when they face unfavorable conditions like starvation?
What happens to bacteria when they face unfavorable conditions like starvation?
What type of DNA do prokaryotic cells primarily contain?
What type of DNA do prokaryotic cells primarily contain?
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Which of the following statements is true regarding metachromatic granules?
Which of the following statements is true regarding metachromatic granules?
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What is the primary component of the bacterial cell wall?
What is the primary component of the bacterial cell wall?
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Which structure is responsible for the motility of bacteria?
Which structure is responsible for the motility of bacteria?
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What defines a monomorphic bacterium?
What defines a monomorphic bacterium?
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What role does lipopolysaccharide (LPS) play in Gram-negative bacteria?
What role does lipopolysaccharide (LPS) play in Gram-negative bacteria?
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Which of the following structures is found in all bacteria except Mycoplasma species?
Which of the following structures is found in all bacteria except Mycoplasma species?
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What is the function of teichoic acids in Gram-positive bacteria?
What is the function of teichoic acids in Gram-positive bacteria?
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What happens to bacteria that lose their cell walls?
What happens to bacteria that lose their cell walls?
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What is the main characteristic of acid-fast bacteria during staining?
What is the main characteristic of acid-fast bacteria during staining?
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What is referred to as the glycocalyx when it is firmly attached to the cell wall?
What is referred to as the glycocalyx when it is firmly attached to the cell wall?
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What is the primary function of the flagella in bacteria?
What is the primary function of the flagella in bacteria?
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Which component of bacterial ribosomes is not present in eukaryotic ribosomes?
Which component of bacterial ribosomes is not present in eukaryotic ribosomes?
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What structure protects bacterial cells from phagocytosis?
What structure protects bacterial cells from phagocytosis?
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Which of the following is a characteristic of Gram-negative bacteria?
Which of the following is a characteristic of Gram-negative bacteria?
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What role does the slime layer play in bacterial adhesion?
What role does the slime layer play in bacterial adhesion?
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Which of the following describes the composition of the bacterial plasma membrane?
Which of the following describes the composition of the bacterial plasma membrane?
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What is the size of bacterial ribosomes?
What is the size of bacterial ribosomes?
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What characteristic distinguishes Gram-positive bacteria from Gram-negative bacteria?
What characteristic distinguishes Gram-positive bacteria from Gram-negative bacteria?
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Which of the following accurately describes the cytoskeleton in prokaryotic cells?
Which of the following accurately describes the cytoskeleton in prokaryotic cells?
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Which nutrient reserves can be found in bacterial inclusions?
Which nutrient reserves can be found in bacterial inclusions?
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What is the significance of metachromatic granules in certain bacteria?
What is the significance of metachromatic granules in certain bacteria?
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Under which conditions do certain bacteria form endospores?
Under which conditions do certain bacteria form endospores?
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What type of glycocalyx structure is loosely attached to the bacterial cell wall?
What type of glycocalyx structure is loosely attached to the bacterial cell wall?
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Which of the following components is NOT involved in the composition of bacterial ribosomes?
Which of the following components is NOT involved in the composition of bacterial ribosomes?
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What term describes the layer that protects bacteria from phagocytosis?
What term describes the layer that protects bacteria from phagocytosis?
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Which structure in bacteria serves as the primary site of protein synthesis?
Which structure in bacteria serves as the primary site of protein synthesis?
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What characteristic distinguishes the flagella of Gram-negative bacteria?
What characteristic distinguishes the flagella of Gram-negative bacteria?
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Which type of antigen is associated with the glycocalyx of bacteria?
Which type of antigen is associated with the glycocalyx of bacteria?
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What distinguishes Mycoplasma from other bacteria regarding cell membrane components?
What distinguishes Mycoplasma from other bacteria regarding cell membrane components?
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Which of these structures is essential for bacterial motility?
Which of these structures is essential for bacterial motility?
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What is the function of lipopolysaccharide (LPS) in the bacterial cell wall?
What is the function of lipopolysaccharide (LPS) in the bacterial cell wall?
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Which of the following is NOT a feature of the bacterial cell wall?
Which of the following is NOT a feature of the bacterial cell wall?
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What distinguishes monomorphic bacteria from pleomorphic bacteria?
What distinguishes monomorphic bacteria from pleomorphic bacteria?
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Which structure is crucial for the bacterial cell to maintain its shape?
Which structure is crucial for the bacterial cell to maintain its shape?
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What is the immediate consequence for bacteria that lose their cell wall?
What is the immediate consequence for bacteria that lose their cell wall?
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What role do fimbriae/pili play in bacterial physiology?
What role do fimbriae/pili play in bacterial physiology?
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Which of the following components is responsible for the Gram staining reaction?
Which of the following components is responsible for the Gram staining reaction?
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Study Notes
Bacterial Cell Structure
- Medical microbiology studies microbes and their interactions with hosts, leading to infectious diseases.
- Cocci: Round-shaped bacteria. Bacilli are rod-shaped, which may have tapered ends. Coccobacilli are short rod-shaped. Spirals have one or more twists.
- Shape and arrangement: Cocci, coccobacilli, vibrio, bacilli, spirillum, and spirochete are examples of bacterial shapes.
- Size: Bacteria range in size from 0.2 to 5 micrometers (μm).
- Monomorphic: Have a single shape.
- Pleomorphic: Have various shapes.
- Light and electron microscopes are used in microbiology to view bacteria.
- Examples of bacterial shapes include coccus, coccobacillus, vibrio, bacillus, spirillum, and spirochete.
Bacterial Cell Structures (External)
-
Glycocalyx: Gelatinous layer of polysaccharide or polypeptide.
- Capsule: Firmly attached to the cell wall, protects the bacteria from phagocytosis, aids in attachment to surfaces.
- Slime layer: Loosely attached, aids in attachment to surfaces.
- Protects bacteria from phagocytosis. Involves bacterial adhesion to surfaces.
- Flagella: Long helical structures composed of flagellin, anchored by a basal body, move the bacteria towards nutrients.
- Fimbriae/pili: Hair-like appendages formed of pilin. They are more numerous, shorter, and thinner than flagella. They promote attachment.
Bacterial Cell Structures (Internal)
-
Cell wall: Located outside the cytoplasmic membrane, composed of peptidoglycan (in nearly all bacteria, except Mycoplasma). Peptidoglycan is composed of N-acetylglucosamine and N-acetylmuramic acid.
- Provides support and rigidity to the cell.
- Cytoplasmic membrane: Thin, elastic membrane below the cell wall; composed of phospholipids and proteins. Functions in semipermeability, energy production (ATP), and biosynthesis.
- Cytoplasm: Semi-transparent substance within the membrane; contains nucleoid, ribosomes, and inclusions.
- Nucleoid: Region containing a single, circular DNA molecule (no nucleus).
- Ribosomes: Structures for protein synthesis (70S ribosomes). Made up of large and small subunits (50S and 30S).
- Inclusions: Stored nutrients like protein, lipids, or glycogen, visible under a microscope.
Gram-Positive and Gram-Negative Cell Walls
- Gram-positive: Thick peptidoglycan layer, with teichoic acids outside.
- Gram-negative: Thinner peptidoglycan layer; have an outer membrane containing lipopolysaccharide (LPS). This layer contains lipoprotein and phospholipids. The periplasmic space is between the outer membrane and the peptidoglycan layer. It contains enzymes like beta-lactamases.
Atypical Cell Walls
- Acid-fast bacteria: Resist staining by Gram stain, retain a dye (e.g., carbol fuchsin) under acid wash.
-
Cell wall deficient bacteria:
- Mycoplasma: Lacks a cell wall.
- L-forms: Bacteria that lose their cell walls and swell, forming irregular shapes.
- Protoplasts and spheroplasts: Gram-positive and Gram-negative cells with a cell wall removed.
Bacterial Spores
- Some bacteria form endospores in unfavorable conditions (starvation, desiccation, heat).
- Genus Clostridium and Bacillus.
- Spores are highly resistant to environmental stress.
- Spores germinate into active bacterial cells upon exposure to nutrients.
Cell Wall Function
- Structural support: Maintains the shape of the bacterium.
- Toxicity: Lipopolysaccharide (LPS) acts as an endotoxin.
- Antigenic: Cell wall components act as antigens.
- Gram staining reaction: Determined by cell wall structure.
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