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Questions and Answers
What is the primary function of bacterial ribosomes?
What do mesosomes develop from?
Which of the following is NOT a characteristic of bacterial spores?
What is the sedimentation rate of bacterial ribosomes?
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Which two genera of Gram-positive bacilli are known for forming highly resistant spores?
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What component of the spore core contributes to heat resistance?
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Which process is indicated by the presence of spores?
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What happens during the germination of bacterial spores?
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What type of flagellar arrangement is characterized by a tuft of flagella at one end?
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Which type of pili is involved in the transfer of genetic material between bacterial cells?
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What is one of the functions of the cytoplasmic membrane in bacterial cells?
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Which of the following describes the nucleoid in bacterial cells?
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What component of the cytoplasm includes molecules essential for metabolic processes?
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Which type of flagellar arrangement has flagella surrounding the entire bacterial cell?
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What is the typical size range of plasmid DNA compared to chromosomal DNA in bacteria?
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What structure is found in the cytoplasm and acts as a barrier selectively allowing substances to enter or exit the cell?
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What is the primary function of the bacterial cell wall?
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Which of the following is not a component of the bacterial cell?
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How does the structure of peptidoglycan differ in Gram-positive and Gram-negative bacteria?
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What two derivatives of glucose make up the backbone of peptidoglycan?
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What percentage of the cell wall does peptidoglycan compose in Gram-positive bacteria?
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Which antibiotic inhibits the synthesis of peptidoglycan?
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What type of bacteria has an outer membrane as part of its cell wall structure?
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What structural feature provides Gram-positive bacteria with rigidity?
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What structure protects the cytoplasmic membrane of the cell from bursting in hypotonic solutions?
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What are protoplasts?
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What is the role of the capsule in bacteria?
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Which bacterial structure is primarily responsible for motility?
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What is a characteristic feature of Mycoplasma?
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Which type of flagellar arrangement has a single polar flagellum?
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What is the significance of flagellar antigens in bacteria?
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Which of the following can revert to its parental form once a cell wall inhibitor is removed?
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What is a major function of teichoic acids in Gram-positive bacteria?
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What components make up the lipopolysaccharides (LPS) in the outer membrane of Gram-negative bacteria?
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Why are Gram-negative bacteria generally more resistant to antibiotics than Gram-positive bacteria?
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What is one of the main functions of lipoprotein molecules (LPP) in Gram-negative bacteria?
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What role does the periplasmic space play in Gram-negative bacteria?
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Which statement is true regarding endotoxins in Gram-negative bacteria?
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What differentiates Gram-positive from Gram-negative bacteria primarily?
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What is the consequence of the structural differences between Gram-positive and Gram-negative bacteria?
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Study Notes
Bacterial Cell Structure
- Bacterial cells are smaller and simpler than eukaryotic cells, lacking recognizable organelles.
- All cellular activities happen in bacteria, though not in specialized structures.
- Bacteria have broad metabolic capabilities and can grow and divide rapidly in various environments.
- Anton van Leeuwenhoek first observed bacteria in 1676.
Bacterial Cell Walls
- Function: The cell wall maintains the cell shape, protecting against physical and chemical stresses. Metabolic activities are often cell wall-dependent.
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Gram-positive cell walls:
- Primarily composed of a thick peptidoglycan layer (about 50-90%).
- Contain teichoic acid layers.
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Gram-negative cell walls:
- Composed of a thin peptidoglycan layer (only 5-20%).
- Have an outer membrane, outside the peptidoglycan layer, composed of lipopolysaccharides (LPS), phospholipids and proteins.
Peptidoglycan
- Peptidoglycan is the main component of bacterial cell walls.
- Its structure: alternating sugars (N-acetylglucosamine (NAG) and N-acetyl muramic acid (NAM)) linked by peptide bridges.
- Synthesis is inhibited by some antibiotics like penicillins and cephalosporins. It can be broken down by lysozyme.
Teichoic Acid
- Located in Gram-positive cell walls.
- It's a major surface antigen in Gram-positive bacteria.
- Induces the production of inflammatory mediators such as TNF-α and IL-1.
Outer Membrane (Gram-negative)
- Found only in Gram-negative bacterial cell walls.
- Composed of lipopolysaccharides (LPS), phospholipids, and proteins.
- LPS includes a lipid A region (toxic), a core polysaccharide, and an outer polysaccharide (somatic or O antigen).
Lipoprotein Molecules
- Found in Gram-negative bacteria.
- Link the peptidoglycan layer and the LPS layer in the cell wall.
- Plays roles in host tissue adherence, bacterial virulence factors, and antibiotic resistance.
Periplasmic Space
- Present only in Gram-negative bacteria.
- A gel-like matrix between the inner cytoplasmic membrane and outer membrane.
- Site of enzymes (e.g. B-lactamases) that degrade certain antibiotics (like penicillin).
Cell Wall Functions
- Maintains cell shape.
- Protects the cell membrane from lysis in hypotonic environments.
- Plays a role in cell division.
- Influences the response to Gram staining.
Cell Wall Deficient Bacteria
- Protoplasts, spheroplasts, and L-forms are examples.
- These lack cell walls and can be produced by treating cells with lysozyme or penicillin.
- L-forms can revert back to the parental form if the cell wall inhibitor is removed.
Mycoplasma
- A type of bacteria that naturally lacks a cell wall.
- They are pleomorphic and resistant to penicillin.
Gram-Positive vs. Gram-Negative Comparison
- Note the differences in cell wall thickness, peptidoglycan content, and the presence of teichoic acid, outer membrane, and lipopolysaccharides (LPS) .
- This differences impact antibiotic effectiveness.
External Structures
- Capsule: Gelatinous layer (glycocalyx), which can be slime or capsule, protecting bacteria from phagocytosis, and can help bacteria adhere to surfaces. It has medically important uses.
- Flagella: Long thread-like appendages used for bacterial motility (movement).
- Pili/Fimbriae: Thin hair-like structures helping in bacterial adhesion to surfaces, and in some cases, genetic transfer. Includes sex pili for DNA transfer.
Cytoplasmic Membrane
- Semipermeable lipid bilayer (phospholipid) around the cytoplasm.
- Found inside the cell wall.
- Key function in transport, energy production, metabolism, and bacterial replication.
Cytoplasm
- Gel-like region within the cytoplasmic membrane containing ribosomes, chromosome, plasmids, and essential cellular components for metabolism and growth.
Nucleoid
- Region of the cytoplasm where the bacterial chromosome is located. Unlike eukaryotic cells, bacteria do not have a true nucleus.
Plasmids
- Extra-chromosomal DNA found in bacteria.
- Contain genes for antibiotic resistance or virulence.
Ribosomes
- Cellular structures composed of RNA and protein.
- Synthesize proteins in the cytoplasm.
- Bacterial ribosomes are smaller than eukaryotic ones (sedimentation rate of 70S).
Mesosome
- Membrane structures that invaginate into the cell for particular functions, including DNA replication and sporulation, and function similarly to eukaryotic cell's respiratory enzymes.
Bacterial Spores
- Highly resistant structures formed under unfavorable conditions (low nutrients, temperature changes).
- Have a protective outer layer.
- Medical importance as indicators for sterilization processes or potential biological weapons.
Summary of Key Bacterial Structures
- Cell wall (thick or thin, Gram+),
- Capsule,
- Flagella,
- Pili,
- Cytoplasmic membrane,
- Cytoplasm,
- Nucleoid,
- Plasmids,
- Ribosomes,
- Mesosomes,
- Spores.
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Description
Explore the fundamental characteristics of bacterial cells, including their structure, metabolic capabilities, and the role of cell walls. Learn about the differences between gram-positive and gram-negative bacteria, as well as the importance of peptidoglycan in maintaining cell integrity.
