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Questions and Answers
Which of the following statements is true about plasmids?
What is a primary function of flagella in bacteria?
Which statement correctly differentiates between flagella and pili?
What characterizes bacterial endospores?
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What is the significance of the H antigen related to flagella?
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What is the primary function of the bacterial cell wall?
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Which of the following is a characteristic of Gram-positive bacteria compared to Gram-negative bacteria?
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Which component is NOT part of the cytoplasmic membrane?
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What role does the capsule play in pathogenic bacteria?
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What are ribosomes composed of in bacterial cells?
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Which component characterizes the cytoplasmic membrane?
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The term 'nucleoid' refers to what structure in bacterial cells?
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Which function is NOT associated with the cell wall of bacteria?
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Which of the following statements about prokaryotes is true?
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What is the primary difference between Gram positive and Gram negative bacteria?
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Which of the following microorganisms can replicate through budding or mitosis?
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What type of ribosome is found in eukaryotic cells?
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Which of the following statements about viruses is correct?
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Which of the following shapes can bacteria exhibit?
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Which characteristic is not true for bacteria?
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What is the size range of bacteria?
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Study Notes
Medical Microbiology
- Medical Microbiology is the study of microbes and their interactions with their hosts, specifically including the study of infectious diseases.
- Microorganisms are living organisms that can only be seen using a microscope.
- Viruses are not considered true organisms as they lack the necessary infrastructure to be truly considered living.
Prokaryotes and Eukaryotes
- Prokaryotes lack a true nuclear membrane, while Eukaryotes have a true one.
- Prokaryotes have one copy of their chromosomal DNA, which is considered haploid, whereas Eukaryotes have two copies of their chromosomal DNA, which is considered diploid.
- Prokaryotes have 70s ribosomes, while Eukaryotes have 80s ribosomes.
- Prokaryotes do not undergo mitosis while Eukaryotes do.
- Bacteria and Viruses are examples of Prokaryotes.
- Fungi are examples of Eukaryotes.
Classes of Pathogenic Microorganisms
- Pathogenic organisms like viruses, bacteria, and fungi have vastly different characteristics.
Viruses
- Viruses are small, ranging from 0.02 to 0.2 µm.
- Viruses lack a nucleus and ribosomes.
- They are composed of either RNA or DNA.
- Viruses replicate intracellularly.
- They cannot achieve motility by themselves.
- The cell wall of viruses is made of protein or lipoprotein.
- Viral growth is limited to intracellular conditions.
Bacteria
- Bacteria are larger, ranging from 1 to 5 µm.
- Bacteria have a nuclear body.
- They have 70s ribosomes.
- They are composed of both RNA and DNA.
- Bacteria replicate through binary fission.
- Some bacteria are capable of motility.
- The cell wall of bacteria are composed of peptidoglycans.
- Bacteria grow both intracellularly and extracellularly.
Fungi
- Fungi are larger, ranging from 3 to 10 µm, specifically yeast are 3 to 10 µm.
- Fungi have true nuclei.
- They have 80s ribosomes.
- They are composed of both RNA and DNA.
- Fungi replicate through budding and mitosis.
- Fungi do not achieve motility by themselves.
- The cell wall of fungi is composed of Chitin.
- Fungi grow in the same way as Bacteria.
Morphology of Bacteria
- The size of bacterial cells is measured by microns, where 1 micron is equal to 1/1000 mm.
- Gram stains are used to differentiate bacteria into gram-positive and gram-negative categories.
- Gram-positive bacteria appear violet when using a Gram stain.
- Gram-negative bacteria appear pink when using a Gram stain.
Shapes of Bacteria
- Cocci are spherical in shape, for example, Staphylococci.
- Bacilli are cylindrical in shape, for example, Diphtheria.
- There are also Spiral, curved, and comma-shaped bacteria.
Arrangements of Bacteria
- Bacteria can be found in many arrangements:
- As single cells, such as Gram-negative bacilli (E. coli).
- In pairs, such as Neisseria and pneumococci.
- In tetrads, such as staphylococci.
- In grape-like clusters, such as staphylococci.
- In chains, such as streptococci and Anthrax bacilli.
- In angular arrangements, such as Diphtheria bacilli.
Bacterial Structure
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Bacterial cells are composed of three main components:
- Cell envelope, which contains the cell wall, cytoplasmic membrane, and capsule.
- Cytoplasmic components, which include the nuclear body, plasmid, and ribosomes.
- Cell appendages, which include flagellae and fimbriae (pili).
Cell Envelope
- The cell wall is the layer that lies outside the cytoplasmic membrane.
- All bacterial cell walls contain peptidoglycan.
Differences between Gram-Positive and Gram-Negative Bacterial Cell Walls
- Gram-positive bacteria have a thick peptidoglycan layer.
- Gram-positive cell walls contain special components including teichoic acid and lipoteichoic acid, and polysaccharides.
- Gram-negative bacteria have a very thin peptidoglycan layer.
- Gram-negative cell walls contain special components including:
- Lipopolysaccharides (endotoxins)
- Lipopolysaccharides
- Outer membrane
- Periplasmic space
Functions of the Cell Wall
- Maintaining the shape of the cell.
- Providing protective function
- Regulating cell permeability.
- Contributing to antigenicity.
- Determining staining reactions.
- Contributing to toxicity.
- Being the target action for antibiotics, such as penicillin and cephalosporins.
Cytoplasmic Membrane
- The cytoplasmic membrane is a thin, elastic membrane that is located directly beneath the cell wall.
- It is primarily composed of protein and phospholipids.
Functions of the Cytoplasmic Membrane
- Facilitating transport and permeability functions.
- Excreting hydrolytic enzymes and toxins.
- Performing biosynthetic functions.
- Contributing to chemotactic functions.
- Energy production (by Mesosomes).
Capsule
- Capsules are gelatinous materials that surround bacterial cells.
- Capsules are produced by some pathogenic bacteria in host tissues.
Chemical Composition of Capsules
- All bacteria possess complex polysaccharides, for example, Streptococcus pneumoniae
- Some bacteria produce polypeptide capsules, for example, Bacillus anthracis
Functions of the Capsule
- Protecting the bacterial cell from phagocytosis.
- Determining the organism's virulence.
- Serving as an antigen.
Cytoplasmic Components
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Ribosomes:
- Function as the protein synthesis factories in the cell
- Composed of RNA and proteins.
- Targeted by some antibiotics, such as tetracycline and chloramphenicol.
- Bacterial ribosomes consist of two subunits:
- Large subunit: 50S.
- Small subunit: 30S.
-
Nuclear Body (Nucleoid):
- Lack a nuclear membrane.
- Composed of folded DNA molecules.
- Contains a single chromosome, which is double stranded circular DNA.
- Carries genetic information.
-
Plasmids:
- Extrachromosomal genetic elements.
- Circular double-stranded DNA molecules.
- Carry specific functions, such as antibiotic resistance.
Cell Appendages
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Flagellae:
- Long helical filaments attached to the cytoplasm.
- Pass through the cell wall.
- Composed of the contractile protein flagellin.
- Demonstrated by:
- Motility tests, such as hanging drop and semisolid agar.
- Electron microscopy.
- Functions:
- Providing motility.
- Serving as an antigen (H antigen).
-
Fimbriae (Pili):
- Short, hair-like filaments, shorter and thinner than flagella.
- Do not originate from the cytoplasm.
- Composed of the protein pilin.
- Functions:
- Adhesion to host cells (common pili).
- Sexual conjugation (sex pili).
- Determining virulence.
Key Differences between Flagellae and Pili
- Size: Flagella are long, Pili are short.
- Shape: Flagella are helical, Pili are straight.
- Composition: Flagella are composed of flagellin, Pili are composed of pilin.
- Function: Flagella aid in motility, Pili aid in adhesion and provide a role in conjugation.
Bacterial Spores
- Bacterial endospores are highly resistant resting bodies formed in response to unfavorable conditions.
- Produced outside the body by some organisms like Bacillus and Clostridium.
- Can be spherical or oval in shape.
- Located centrally, sub-terminally, or terminally.
- Contain dipicolinic acid.
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Description
Test your knowledge on Medical Microbiology, including the distinctions between prokaryotes and eukaryotes, as well as classes of pathogenic microorganisms. This quiz covers essential concepts related to microbes, their structure, and their interactions with hosts. Challenge yourself and enhance your understanding of infectious diseases!
