Bacteriophage Biology Quiz

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Questions and Answers

What is the main function of the tail of a bacteriophage?

To protect the nucleic acid core

To replicate the phage's genetic material

To synthesize proteins

To attach to the bacterial cell surface (correct)

What is the difference between a lytic bacteriophage and a symbiotic bacteriophage?

Lytic phages destroy the host cell, while symbiotic phages do not. (correct)

Lytic phages replicate inside the host cell, while symbiotic phages do not.

Lytic phages have tails, while symbiotic phages do not.

Lytic phages are RNA viruses, while symbiotic phages are DNA viruses.

Which of the following statements is true about the nucleic acid core of a bacteriophage?

It is composed entirely of DNA.

It can be either DNA or RNA. (correct)

It is composed of both DNA and RNA.

It is composed entirely of RNA.

What is the function of the contractile sheath in a bacteriophage?

To inject the phage's genetic material into the host cell (D) Signup and view all the answers

What is the main difference between the relaxed stage and the contracted stage of the bacteriophage tail?

The relaxed stage is used for attachment, while the contracted stage is used for injection. (C) Signup and view all the answers

What is the main role of RNA phages in chromosome conjugation?

They act as vectors for transferring DNA between bacteria. (A) Signup and view all the answers

What is the term for the process by which a bacteriophage integrates its genetic material into the host cell's genome?

Lysogeny (B) Signup and view all the answers

Which of the following is an example of a disinfectant that is not a biological agent?

Hydrogen peroxide (B) Signup and view all the answers

What is the function of the "plus" chain of RNA in RNA phage replication?

It serves as a template for the synthesis of the "minus" chain. (B) Signup and view all the answers

During the replication of RNA phages, what is the role of the double-stranded RNA intermediate?

It serves as a template for the production of new capsid proteins. (D) Signup and view all the answers

What is the primary mechanism by which new RNA phage particles are released from the host bacterium?

Cell lysis. (D) Signup and view all the answers

Which of the following is NOT a key characteristic of the lysogenic cycle in bacteriophages?

Lysis of the host bacterium. (B) Signup and view all the answers

What is the term for a bacteriophage capable of establishing a symbiotic relationship with a bacterial host?

Temperate bacteriophage. (D) Signup and view all the answers

What is the significance of the ‘circularization’ of phage DNA during the lysogenic cycle?

It allows the phage DNA to integrate into the host bacterial chromosome. (D) Signup and view all the answers

Which of the following best describes the relationship between a lysogenic bacterium and a temperate bacteriophage?

Mutualism: both the phage and the bacterium benefit from the relationship. (B) Signup and view all the answers

What is the primary reason why lysogenic bacteria are resistant to infection by another homologous bacteriophage?

The presence of the prophage in the bacterial chromosome prevents the integration of another homologous phage. (B) Signup and view all the answers

Which of the following antibiotics act by inhibiting protein synthesis?

Tetracycline (A) Signup and view all the answers

How do quinolones, like Ciprofloxacin, exert their antibacterial effect?

By interfering with DNA replication through DNA gyrase inhibition (B) Signup and view all the answers

Which of the following mechanisms is NOT a common mechanism of acquired bacterial resistance to antibiotics?

Increased production of essential metabolites, like folic acid (C) Signup and view all the answers

Which of the following antibiotics acts by inhibiting the synthesis of RNA?

Rifampicin (D) Signup and view all the answers

How do macrolides, like Clarithromycin and Azithromycin, inhibit protein synthesis?

By preventing the translocation of the peptide chain along the ribosome (C) Signup and view all the answers

Which of the following is an example of a drug that acts by interfering with folic acid synthesis?

Sulfamethoxazole (B) Signup and view all the answers

Which of the following is a common mechanism of bacterial resistance to antibiotics like penicillin?

Production of enzymes that inactivate the antibiotic (A) Signup and view all the answers

Which of the following accurately describes the difference between natural and acquired resistance to antibiotics?

Natural resistance is genetically determined, while acquired resistance is developed through exposure to antibiotics. (B) Signup and view all the answers

What type of resistance is exhibited when a germ is resistant to multiple antibiotics?

Multivalent resistance (C) Signup and view all the answers

Which of the following is NOT a characteristic of microorganisms (bacteria, microbes)?

They are visible with the naked eye. (B) Signup and view all the answers

What type of resistance develops through mutations in the bacterial chromosome?

Chromosomal resistance (C) Signup and view all the answers

What is the size range of most bacteria, expressed in micrometers?

1 - 10 µm (A) Signup and view all the answers

What is the defining characteristic of a bacterial cell?

Lack of a nucleus (D) Signup and view all the answers

What is the term for the study of microorganisms?

Microbiology (C) Signup and view all the answers

Which of the following is NOT a type of resistance development based on the rhythm of installation?

Extrachromosomal resistance (D) Signup and view all the answers

What is the term for when a bacterial cell divides into two identical cells?

Binary fission (A) Signup and view all the answers

What is the primary function of the spore cortex in bacterial spores?

Protects the spore from lysozyme (B) Signup and view all the answers

What is the role of calcium dipicolinate in bacterial spores?

Contributes to the heat resistance of the spore (B) Signup and view all the answers

Which of the following structures is directly involved in the division of bacterial DNA?

Mesosome (B) Signup and view all the answers

Which of the following processes occurs during the separation phase of bacterial cell division?

Formation of a new cell wall between the daughter cells (C) Signup and view all the answers

What is the significance of the 'semiconservative' division model in bacterial cell division?

Each daughter cell receives half of the parental chromosome (B) Signup and view all the answers

Which of the following is a characteristic of bacterial cell division through binary fission?

Results in the production of two daughter cells with identical genetic material (D) Signup and view all the answers

What is the primary function of bacterial metabolism?

To promote growth and multiplication (B) Signup and view all the answers

What are the two main categories of bacterial variability?

Phenotype variation and genotype variation (C) Signup and view all the answers

What is the primary mechanism responsible for natural mutations in bacteria?

Errors during DNA replication (B) Signup and view all the answers

Which of the following mechanisms of genetic transfer involves the direct transfer of DNA from a donor bacterium to a recipient bacterium through a pilus?

Conjugation (B) Signup and view all the answers

What is the term used to describe a bacterial cell that is capable of taking up foreign DNA during transformation?

Competent (B) Signup and view all the answers

Which type of mutation involves a change in a single nucleotide base within a gene?

Point mutation (B) Signup and view all the answers

What type of genetic element can move from one location to another within a bacterial genome?

Both B and C are correct (B) Signup and view all the answers

Which of the following mechanisms involves the transfer of DNA from a donor bacterial cell to a recipient cell via a bacteriophage?

Transduction (B) Signup and view all the answers

What are bacteriocins and what is their function?

Bacteriocins are proteins that can kill other bacterial strains. (C) Signup and view all the answers

Study Notes

Bacterial Definitions

Bacteriostatic agent: Stops the multiplication of bacteria. Multiplication resumes after removing the agent.
Bactericidal agent: Kills the bacterial cell. The process is irreversible; bacterial multiplication won't occur even after removing the agent.

Actions and Definitions

Sterilization: The process of eliminating all microbial flora.
Disinfectant: A substance used to inactivate microorganisms in specific areas (e.g., tables, floors), but is too toxic for use on human tissue.
Disinfection: The inactivation of microorganisms from surfaces (inanimate objects).
Antisepsis: Applying bactericidal or bacteriostatic substances to kill or inhibit the growth of pathogenic flora in wounds.
Asepsis: All measures that prevent contamination from infectious agents.
Conservation: Preventing spoilage of degradable products (e.g., food, drugs) by microbial agents.

Physical Agents

Heat:
- Dry heat sterilization: flaming, dry heat oven.
- Moist heat sterilization: boiling, pasteurization, tyndallisation, autoclaving.
- Dryness (desiccation)
- Lyophilisation: gradual drying in vacuum at low temperatures (-40°C to 70°C).
Mechanical pressure
Osmotic pressure
Radiations
Ultrasounds
Electricity
Filtering: Passing thermo-sensitive fluids through sterilizing filters to capture microorganisms.

Chemical Agents

Phenol and derivatives: Bactericidal action by lysing bacterial cells.
Alcohols: Weaker than phenol; act bactericidally only on vegetative forms.
Halogens and halogenated compounds: Often used as antiseptics and disinfectants (e.g., chlorine, iodine); have powerful bactericidal and sporicidal action.
Acids and bases: Bactericidal action by distorting bacterial proteins.
Salts: Heavy metals have the strongest bactericidal effect.
Formaldehyde and Glutaraldehyde
Gaseous disinfectants: Ethylene oxide is the best for dry surfaces.
Soaps and detergents (surfactants)
Metabolic antagonists
Dyes
Others: Hydrogen peroxide, potassium permanganate.

Biological Agents: Bacteriophages

Bacteriophages: Viruses that can lyse bacterial cells (lytic bacteriophages) or not (symbiotic bacteriophages).
Morphology and chemical composition:
- DNA phages
- RNA phages
- The head contains nucleic acid core and a protein shell (capsid). The nucleic acid core is mainly DNA and makes up about 50% of the dry weight. The protein shell gives the head a polygonal shape with identical protein subunits forming a hexagonal prism.
- The tail is used for attachment to the bacterial cell surface. It has three sections: lacunar middle, contractile sheath and basal terminal plate. The plate has attached tail fibers.
The tail can exist in two functional phases: relaxed and contracted stages.
In addition to the normal form, there may be bacteriophages without tails and also filamentous bacteriophages.
RNA phages have a specific morphology with a molecular weight of 4x10^6 Daltons, self-complementary complex tertiary structure and capsids composed of 180 subunits (capsomeres). They are involved in chromosome conjugation and lysogenization of intestinal bacteria.

Types of Interrelations Between Bacteriophages and Bacteria

The bacteriophage is a bacterial virus, with bacteria as its host.
Attachment to the bacterial surface occurs through receptors.
Lyso-sensitive bacteria allow the attachment and entry of bacteriophages.
Lyso-resistant bacteria do not allow this attachment and entry.
Lytic relation: Phages penetrate the cell, causing cell death and releasing new bacteriophage particles.
Steps of the lytic cycle:
- Adsorption
- Penetration
- Intracellular replication (DNA phage replication, then RNA phage replication)
- Maturation of phage particles
- Release of phage particles
Adsorption: The attachment of the phage to receptors on the surface of a lyso-sensitive bacterial cell.
Penetration: The phage injecting its nucleic acid into the bacterium.
Intracellular replication: Viral DNA replicates, using host cell machinery, and new phage components are synthesized.
Maturation: Assembled phage particles and components are produced.
Release: Newly formed phages are released, usually by cell lysis.
Symbiotic relation: Entry of the bacteriophage into the bacterial cell without causing lysis, with genetic material integration into the bacterial chromosome (called lysogeny). -Prophages: bacteriophages able to establish a symbiotic relationship with specific host bacteria. The stages of the symbiotic phage infection are adsorption, penetration of phage nucleic acid, circularization of DNA phage and coupling circular DNA phage with bacterial DNA. -Lysogenic bacteria are resistant ('immune') to infection by the same bacteriophage due to the release of a 'repressor' substance inhibiting the multiplication of the lytic phage inside the cell. -Inducing agents lead to the inactivation of the repressor, therefore, causing a change of certain cell properties (called 'conversion').

Bacterial Genetics

Bacterial genetics: Studies heredity and variability in bacteria.
Heredity: The property of living organisms to pass on specific characteristics to their offspring.
Variability: Hereditary changes in bacteria.
Genetic material organization in bacteria: The bacterial genome consists of replicons, which are functional genetic units that can replicate independently. This includes the bacterial chromosome and extrachromosomal genetic elements (such as plasmids and transposable elements).

Bacterial Heredity

Bacterial characteristics are genetically determined; their expression is reflected in the phenotype.
The bacterial genome consists of replicons (genetic configurations that replicate independently).
- Bacterial chromosome
- Extrachromosomal genetic elements
- Genetic transposable elements

Bacterial Nuclear Area

The bacterial nuclear area (nucleoid) is the irregularly shaped region that contains the genetic material (DNA) within the cytoplasm.

DNA Structure

DNA is composed of two complementary strands with reverse polarity, following the Watson and Crick model.
These strands are formed by nucleotides composed of: deoxyribose, phosphoric acid, and nitrogenous bases (adenine, guanine, cytosine, thymine).

DNA Replication

The double helix structure of DNA in bacteria allows for semi-conservative replication at specific sites.
The DNA opens up like a zipper using DNA gyrase.
Each existing strand acts as a template for the synthesis of a complementary strand by DNA polymerase.

Extrachromosomal Elements

Plasmids: Extra-chromosomal genetic formations (circular DNA molecules) that can replicate independently of the bacterial chromosome. Plasmids can be conjugative, meaning they can transfer independently to other bacterial cells; or non-conjugative (they need the help of another conjugative plasmid or bacteriophage). Episomes are a type of extrachromosomal element that can either replicate autonomously or integrate into the chromosome.
- Genetic determinants: Essential genes for replication, but also accessory genes for bacterial survival or virulence factors (e.g., antibiotic resistance, toxins). Some plasmids have no observable effect (cryptic plasmids).
- Resistance plasmids: Circular DNA molecules with genes that confer resistance to one or more types of antibiotics.
- Virulence plasmids: Carry genetic determinants enabling bacteria to produce virulence factors (e.g., toxins, colonization factors).
- F plasmid (plasmid for sex): Carries genes for DNA transfer during bacterial conjugation and it can integrate into the bacterial chromosome mediate chromosomal gene transfer.
- Col Plasmids: Contains genes for antibacterial polypeptides (bacteriocins) which can kill other bacterial strains.
Genetic Transposable Elements: (IS - Insertion sequences; Tn - Transposons.) Fragments of genetic material that can move from one location to another within the genome.
This movement can alter bacterial genes and characteristics, potentially contributing to bacterial variability.

Bacterial Variability

Phenotype variation: Changing bacterial properties by adapting to environmental conditions without altering the genome.
Genotype variation: Changes resulting from genome modifications (mutations, genetic material transfer).
Variation in bacteria is attained through:
- Mutations (spontaneous/induced)
- Transfer of genetic material (transformation, transduction, conjugation, transposition)

Bacterial Mutations

Mutations: Spontaneous or induced changes in the bacterial genome, altering the nucleotide sequence of a gene. - Point mutations: affect one nucleoid, potentially reversible. - Extended mutations: affect multiple genes
Causes of mutations:
- Copying mistakes during self-replication due to speed
- Exposure to mutagens (e.g., X-rays, UV radiation, biological agents) which modify the base sequences.
Consequence of mutations: Individuals with new characteristic traits, such as antibiotic resistance, or pathogenicity.

Transfer of Genetic Material

Transformation: Transfer of pure DNA from a donor to a recipient cell.
Competence: The state where the recipient bacterium allows foreign DNA incorporation.
Competence-positive cells display specific surface antigens ('power factor') to facilitate and allow a more porous and electropositive cell wall. The cell's ability to take up foreign DNA.
Transduction: Transfer of genetic material by bacteriophages. This can either be generalized transduction (any gene can be transferred) or specialized transduction (only certain genes are transferred).
Conjugation: Transfer of genetic material through cell-to-cell contact.
Transposition: Integration of a transposable genetic element into a different place in the genome. Transposable elements, based on their structure and mechanism of translocation, fall into three classes: I, II, and III.

Antibacterial Chemotherapy

Definition: Chemotherapeutics are any substance that inhibits (or kills) microorganisms (bacteria) in small doses. (Can be lethal - bactericidal, or prevent multiplication – bacteriostatic).
Mechanisms of action:
- Metabolic competitive antagonism
- Inhibition of bacterial cell wall synthesis
- Alteration of cytoplasmic membrane function
- Inhibition of bacterial protein synthesis
- Inhibition of bacterial nucleic acid synthesis

Cell Wall Synthesis Inhibitors

Betalactams (penicillins and cephalosporins): Inhibit cell wall synthesis by binding to enzymes involved in the final stage of cross-linking of peptidoglycan chains (PBPs). This leads to secondary accumulation of murein subunits, thus activating the autolytic enzyme system. Resulting in bacterial cell lysis.
Glycopeptides (vancomycin, teicoplanin): Interfere with peptidoglycan elongation.
Bacitracin: Used locally for skin infections; high toxicity.
Isoniazid, cycloserine, ethionamide: Used in treatment of tuberculosis.

Surface and Cytoplasmic Membrane Inhibitors

Surfactants (polymyxins): Destruct bacterial cytoplasmic membrane phospholipid structures.
Amphotericin B, Colistin, Imidazole, Gramicidin Also destruct bacterial membrane by a similar mechanism.

Protein Synthesis Inhibitors

Aminoglycosides: Block formyl-methionyl-t-RNA binding to ribosomes (preventing polypeptide chain initiation) and affect the decoding information on m-RNA.
Tetracyclines (tetracycline, doxycycline): Block aminoacyl-t-RNA attachment to ribosomes, thus inhibiting protein synthesis.
Chloramphenicol: Inhibit peptide bond formation between amino acids.
Macrolides (clarithromycin, azithromycin): Inhibit ribosome translocation of peptide chains.
Lincosamides (clindamycin): Bind to ribosomes, preventing peptide bond formation.
Fusidic acid: Blocks protein synthesis by binding elongation factor to the polypeptide chain on the ribosome.

Nucleic Acid Inhibitors

Rifampicins: Bind to DNA-dependent RNA polymerase, blocking RNA synthesis.
Quinolones (nalidixic acid, ciprofloxacin, norfloxacin, ofloxacin etc): Block DNA gyrase, responsible for DNA supercoiling.
Sulphonamides: Inhibit folic acid synthesis, which is important for DNA and RNA synthesis. Co-trimoxazole is an example.
Sulfones (e.g., dapsone): Are related to sulphonamides and used to treat certain bacterial infections (e.g. leprosy).

Resistance Mechanisms and Types

Natural resistance: Inherent characteristic of certain bacterial species.
Acquired resistance: Resistance developing in susceptible species. This is influenced by different mechanisms such as:
- Production of enzymes that inactivate the antibiotic (e.g., penicillinase).
- Decreased permeability of the bacterial cell wall or cytoplasmic membrane to the antibiotic.
- Development of excess complementary enzymes.
- Alteration of intracellular target (e.g., modification of ribosomal protein).
- Increase in synthesis of substances which interfere with the antibiotic action (e.g., para-amino benzoic acid synthesis in the case of sulfonamides).
Resistance types:
- Monovalent: Resistance to one antibiotic.
- Multivalent: Resistance to multiple antibiotics.
Rhythm of resistance appearance (determined by antibiotic): The rate of resistance development for different classes of antibiotics can differ in terms of swiftness (fast - streptomycin type; intermediate - erythromycin type; slow - penicillin type).

Bacterial Taxonomy and Morphology

Bacterial taxonomy: The science of classifying and naming bacteria.
Bacterial cell structure: Characteristics, shape and dimensions, structural components of the cell wall and the spore form.
- Classification of cocci (spherical, oval, etc).
- Different settlement patterns of cocci.
- Bacteria classification in based on bacilli forms.
  - Different settlement patterns of bacilli.
    - Isolated
    - In chains
    - In palisades. .
  - Bacterial morphological forms: coccobacillus, vibrios, spiral bacteria (e.g. spiral, spirochetes, spirochaetes)
Bacterial cell division: The reproduction process of bacteria involving septation and separation and division of nuclear material.

Microorganism Basic Classification

Basic classification between prokaryotes and eukaryotes: Differences in cell structure, presence of organelles (such as mitochondria), cell size, nucleus.
Prokaryotes are smaller than eukaryotes and don't have organelles or a nucleus.

Bacterial Cell Structure

General characteristics of prokaryotic cells:
Dimensions, generally small (1-10 μm).
Organization is typically unicellular, forming populations.
Major component
- Nucleoid/Nucleus: Region containing the genetic material (DNA), no nucleus or nucleolus.
- Cytoplasmic membrane: A thin elastic membrane that regulates passage of substances between the cell and its environment.
- Cell wall: Provides shape, structural support and protection, and is the target of some antibiotics
- Cytoplasm: Unpartitioned region containing enzymes, ribosomes, and various inclusions.
Additional peripheral elements:
- Annex Elements: Cilia, fimbriae, capsules.
- Spores: Dormant resistant stage of some bacteria.

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Test your knowledge on the structure and function of bacteriophages. This quiz covers key concepts such as lytic vs. symbiotic bacteriophages, replication mechanisms, and the role of RNA phages. Dive into the fascinating world of these viral agents and enhance your understanding of molecular biology.