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Questions and Answers
Which type of bacteria lacks rigid cell walls and is resistant to cell wall-inhibiting antimicrobial agents?
Which type of bacteria lacks rigid cell walls and is resistant to cell wall-inhibiting antimicrobial agents?
What distinguishes curved or spiral-shaped bacteria from other forms?
What distinguishes curved or spiral-shaped bacteria from other forms?
Which of the following statements about bacteria's genetic material is correct?
Which of the following statements about bacteria's genetic material is correct?
Which type of bacterial cell arrangement refers to cocci that form clusters?
Which type of bacterial cell arrangement refers to cocci that form clusters?
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Which characteristic is NOT used to differentiate types of bacteria?
Which characteristic is NOT used to differentiate types of bacteria?
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What unique arrangement characterizes staphylococcus bacteria?
What unique arrangement characterizes staphylococcus bacteria?
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Which type of bacilli has more than two cells arranged in a chain?
Which type of bacilli has more than two cells arranged in a chain?
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What color do gram-negative bacteria appear after a Gram-staining procedure?
What color do gram-negative bacteria appear after a Gram-staining procedure?
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Which statement accurately describes the nucleoid in bacteria?
Which statement accurately describes the nucleoid in bacteria?
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What is the purpose of using methylene blue in simple staining techniques?
What is the purpose of using methylene blue in simple staining techniques?
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Which ions are primarily associated with stabilizing bacterial DNA in the nucleoid?
Which ions are primarily associated with stabilizing bacterial DNA in the nucleoid?
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What distinguishes Gram-positive bacteria from Gram-negative bacteria in staining tests?
What distinguishes Gram-positive bacteria from Gram-negative bacteria in staining tests?
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Which type of bacteria is represented by diplococci?
Which type of bacteria is represented by diplococci?
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What is the primary function of ribosomes in prokaryotic cells?
What is the primary function of ribosomes in prokaryotic cells?
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Which layer of the cell envelope is primarily responsible for maintaining osmotic pressure?
Which layer of the cell envelope is primarily responsible for maintaining osmotic pressure?
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What substances are primarily responsible for the strength of the bacterial cell wall?
What substances are primarily responsible for the strength of the bacterial cell wall?
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Which component is NOT part of the peptidoglycan structure?
Which component is NOT part of the peptidoglycan structure?
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What type of acids are covalently linked to peptidoglycan in Gram-positive bacteria?
What type of acids are covalently linked to peptidoglycan in Gram-positive bacteria?
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In addition to ribosomal RNA (rRNA), what is the composition of ribosomes?
In addition to ribosomal RNA (rRNA), what is the composition of ribosomes?
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Which of the following processes does the cytoplasmic membrane NOT facilitate?
Which of the following processes does the cytoplasmic membrane NOT facilitate?
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Which structure provides a protective barrier against harsh chemicals in prokaryotic cells?
Which structure provides a protective barrier against harsh chemicals in prokaryotic cells?
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Which component of the bacterial flagellum is responsible for its structure and function?
Which component of the bacterial flagellum is responsible for its structure and function?
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What role do adhesins play in the structure of pili?
What role do adhesins play in the structure of pili?
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Which type of bacterial flagella arrangement is characterized by multiple polar flagella?
Which type of bacterial flagella arrangement is characterized by multiple polar flagella?
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What is the primary function of ordinary pili in bacteria?
What is the primary function of ordinary pili in bacteria?
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Which stage of biofilm development involves the formation of structures of closely aggregated bacteria?
Which stage of biofilm development involves the formation of structures of closely aggregated bacteria?
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What best describes the function of endospores in bacteria?
What best describes the function of endospores in bacteria?
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Which of the following statements about biofilms is NOT true?
Which of the following statements about biofilms is NOT true?
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In biofilm formation, what is the primary method by which planktonic bacteria attach to surfaces?
In biofilm formation, what is the primary method by which planktonic bacteria attach to surfaces?
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What is the primary function of the outer membrane in Gram-negative bacteria?
What is the primary function of the outer membrane in Gram-negative bacteria?
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What components make up lipopolysaccharide (LPS)?
What components make up lipopolysaccharide (LPS)?
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Which outer membrane protein is NOT associated with the connection between the outer membrane and murein?
Which outer membrane protein is NOT associated with the connection between the outer membrane and murein?
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How does the glycocalyx differ between the capsule and the slime layer?
How does the glycocalyx differ between the capsule and the slime layer?
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What role does lipid A play in lipopolysaccharide (LPS)?
What role does lipid A play in lipopolysaccharide (LPS)?
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What is the primary function of porins in the outer membrane?
What is the primary function of porins in the outer membrane?
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What structure surrounds the bacterial cell wall in Gram-positive bacteria?
What structure surrounds the bacterial cell wall in Gram-positive bacteria?
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What distinguishes the capsule of Bacillus anthracis from other bacterial capsules?
What distinguishes the capsule of Bacillus anthracis from other bacterial capsules?
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Study Notes
Microbiology
- The study of microorganisms refers to the study of a broad and diverse group of microscopic organisms that exist either as single cells or in clusters.
- Microorganisms include bacteria, fungi, protozoa, algae, and viruses.
Prokaryotes
- Unicellular organisms that lack organelles or other internal membrane-bound structures.
- Lack a nucleus.
- Possess a single chromosome: a piece of circular, double-stranded DNA located in an area of the cell called the nucleoid.
Bacteria
- Have a cell wall.
- Can be normal flora or pathogenic bacteria.
- Reproduce asexually by binary transverse fission.
Mycoplasma
- Bacteria lacking rigid cell walls.
- Some species, like Mycoplasma pneumoniae (an agent of pneumonia), contain sterols in their membrane.
- Lack a target for cell wall-inhibiting antimicrobial agents (e.g., penicillins and cephalosporins), making them resistant to these drugs.
- Found in various forms, the most common being the coccoid cell. Threadlike forms also occur in different lengths.
Bacterial Morphology
- Along with other characteristics, bacterial shape is used for identification.
- Shape is determined by the cell wall assembly mechanism.
- Three basic forms:
- Coccus or Cocci: Spherical bacterial cells (e.g., Staphylococcus aureus).
- Bacilli: Uniform thickness, rounded ends, pointed ends (e.g., Bacillus subtilis).
- Curved or spiral rods: Comma shaped, spiral, screw shaped (e.g., Vibrio cholera, Treponema pallidum).
- Some bacterial species are pleomorphic (e.g., Mycoplasma pneumoniae).
Arrangement of Bacterial Cells
- Cocci and bacilli can be characterized by their aggregation patterns.
- Arrangement is specific to each bacterial species.
Arrangement of Cocci Cells
- Singly: Bacteria appearing as single cells are simply called cocci.
- Diplococci: Cells found in pairs, attached to each other.
- Streptococcus: Bacteria forming long chains, remaining connected.
- Staphylococcus: Bacteria arranged irregularly in clusters resembling grapes.
Arrangement of Bacilli
- Singly: Bacteria existing as single cells, called bacilli.
- Diplobacilli: Bacteria with two rod-shaped cells attached to each other.
- Streptobacilli: Cells arranged as long chains in these bacteria.
Staining
- Light microscopy and chemical staining techniques are generally used to determine bacterial shape.
Simple Staining
- Uses a single staining substance, for example, methylene blue.
Differential Staining
- Employs two stains with differing affinities to different bacteria.
- The most important differential staining technique is Gram staining.
- Gram-positive bacteria stain blue-violet, while Gram-negative bacteria stain red.
Gram Stain
- Most bacteria are classified as either Gram-positive or Gram-negative based on their response to the Gram-staining procedure.
- Procedure named for the histologist Hans Christian Gram, who developed this differential staining technique to stain bacteria in infected tissues.
- Gram stain relies on certain bacteria (the Gram-positive bacteria) retaining a complex of crystal violet (a purple dye) and iodine after a brief wash with alcohol or acetone.
- Gram-negative bacteria do not retain the dye-iodine complex and become translucent. However, they can be counterstained with safranin (a red dye).
- Gram-positive bacteria appear purple under the microscope, while Gram-negative bacteria appear red.
- The distinction between these two groups reflects fundamental differences in their cell envelopes.
The Nucleoid
- Consists of a tangle of double-stranded DNA, not surrounded by a membrane, localized in the cytoplasm.
- Bacterial DNA is haploid.
- DNA is stabilized by small polyamines and Mg ions and associated with histone-like proteins.
Cytoplasm
- Contains numerous solutes, low- and high-molecular weight substances, RNA, and ribosomes.
- Frequently used to store reserve substances (glycogen depots, polymerized metaphosphates, lipids).
Plasmids
- Small, circular, non-chromosomal, double-strand DNA molecules capable of self-replication.
Ribosomes
- Minute particles comprised of ribosomal RNA (rRNA) and protein.
- Bacterial ribosomes consist of two subunits: 50S and 30S.
- These two subunits combine during protein synthesis to form a complete 70S ribosome.
- Ribosomes function to synthesize proteins.
The Cell Envelope
- Prokaryotic cells are surrounded by complex envelope layers that vary in composition among the major groups.
- Includes the inner cell membrane and the cell wall.
- In Gram-negative bacteria, an outer membrane is also part of the envelope.
Functions
- Protects organisms from hostile environments, such as extreme osmolarity, harsh chemicals, and even antibiotics.
The Cytoplasmic Membrane
- Also known as the plasma membrane.
- Primarily a double layer of phospholipids with several proteins integrated into its structure.
- Important membrane proteins include permeases, enzymes for cell wall biosynthesis, transfer proteins for extracellular protein secretion, sensor or signal proteins, and respiratory chain enzymes.
Cell Wall
- Refers to the portion of the cell envelope external to the cytoplasmic membrane and internal to the capsule or glycocalex.
Function
- Protects the protoplasts from the external environment.
- Withstands and maintains the osmotic pressure gradient between the cell interior and the extracellular environment.
- Provides the cell its outer form.
- Facilitates communication with its surroundings.
- The bacterial cell wall owes its strength to a layer composed of a substance known as murein, mucopeptide, or peptidoglycan (all synonyms).
The Peptidoglycan Layer
- A complex polymer consisting of three parts:
- A backbone composed of alternating N-acetylglucosamine and N-acetylmuramic acid connected by β1→4 linkages.
- Identical tetrapeptide side chains attached to N-acetylmuramic acid.
- Identical peptide cross-bridges.
- May contain Diaminopimelic acid, an amino acid unique to bacterial cell walls.
The Cell Wall of Gram-Positive Bacteria
- Composed of:
- Peptidoglycan (50% of the cell wall).
- Teichoic acids and teichuronic acids (water-soluble polymers).
- Polysaccharides.
- Two types of teichoic acids:
- Wall teichoic acid: Covalently linked to peptidoglycan.
- Membrane teichoic acid: Covalently linked to membrane glycolipid.
- Called lipoteichoic acids due to their association with lipids.
The Cell Wall of Gram-Negative Bacteria
- Composed of:
- Peptidoglycan (2%-10% of the cell wall).
- Lipoprotein (cross-links the peptidoglycan and outer membrane).
- An outer membrane.
Outer Membrane
- A phospholipid bilayer, with its inner leaflet resembling the cell membrane in composition.
- The outer leaflet contains a distinctive component, a lipopolysaccharide (LPS).
Functions
- Protects cells from harmful enzymes, some antibiotics, and prevents leakage of periplasmic proteins.
Outer Membrane Proteins
- OmpA (outer membrane protein A) and the murein lipoprotein create a bond between the outer membrane and murein.
- Porins: Proteins forming pores in the outer membrane, allowing passage of hydrophilic, low-molecular-weight substances into the periplasmic space.
- Outer membrane-associated proteins: Constitute specific structures enabling bacteria to attach to host cell receptors.
- Transport proteins: Example includes the LamB proteins for maltose transport.
Lipopolysaccharide (LPS)
- Molecular complex comprised of lipid A, the core polysaccharide, and the O-specific polysaccharide chain.
Function
- Also known as endotoxin, with toxicity associated with lipid A.
- Contains major surface antigenic determinants, including O antigen found in the polysaccharide components.
The Periplasmic Space
- Space between the inner and outer membrane in Gram-negative bacteria.
- In Gram-positive bacteria, a smaller periplasmic space exists between the inner membrane and the peptidoglycan layer.
Glycocalyx
- A network of polysaccharides projecting from cellular surfaces of bacteria, located just outside the bacterial cell wall.
- Two forms:
Capsule
- Well-defined structure of polysaccharide surrounding a bacterial cell, external to the cell wall.
- Exception: The poly-D glutamic acid capsule of Bacillus anthracis.
Functions
- Protects the bacteria from phagocytosis.
- Plays a role in bacterial adherence.
Slime Layer
- A loose network of polysaccharide fibrils surrounding some bacterial cell walls.
- Function: Associated with adhesive properties of the bacterial cell.
Flagella
Structure
- Bacterial flagella are thread-like appendages consisting of a basal body, hook, and a long filament composed of a polymerized protein called flagellin.
- Organs of locomotion for bacteria possessing them.
Types of Arrangement
- Monotrichous: Single polar flagellum.
- Lophotrichous: Multiple polar flagella.
- Peritrichous: Flagella distributed over the entire cell.
Pili (Fimbriae)
- Rigid surface appendages composed of structural protein subunits termed pilins.
- Minor proteins called adhesins are located at the tips of pili, responsible for attachment properties.
Classes
- Ordinary pili: Role in adherence of bacteria to host cells.
- Sex pili: Responsible for the attachment of donor and recipient cells in bacterial conjugation.
Functions
- Ordinary pili: Colonization antigens or virulence factors.
- Antiphagocytic properties.
Endospores
- Resting cells highly resistant to desiccation, heat, and chemical agents.
- When returned to favorable nutritional conditions and activated, the spore germinates to produce a single vegetative cell.
Structure
- Possess a core containing many cell components (a nucleoid, some ribosomes, RNA molecules, and enzymes), a spore wall, a cortex, a coat, and an exosporium.
Biofilm
- An aggregate of interactive bacteria attached to a solid surface or to each other, encased in an exopolysaccharide matrix.
- Matrix typically composed of polysaccharides, proteins, lipids, and DNA.
Benefits of Biofilm Formation
- Resisting attack by antibiotics.
- Trapping nutrients for bacterial growth, remaining in a favorable niche.
- Adhering to environmental surfaces and resisting flushing.
- Living in close association and communicating with other bacteria in the biofilm.
- Protection from the host’s immune mechanisms.
Stages of Biofilm Development
- Attachment: Planktonic bacteria (free individual bacteria not in a biofilm) contact an environmental surface and attach to it using pili or cell wall adhesins.
- Microcolony formation: Bacteria multiply and form a microcolony.
- Biofilm maturation: The biofilm develops into a mature structure with complex architecture and different bacterial populations.
- Dispersion: Some bacteria detach from the biofilm and disperse to colonize new areas.
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Test your knowledge on microorganisms, especially prokaryotes and bacteria. This quiz covers their characteristics, reproduction methods, and the unique features of mycoplasma. Delve into the world of microbial life and their importance in various ecosystems.
