Microbiology Chapter on Gene Transfer

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Questions and Answers

Which mechanism involves the direct transfer of genes through cell-to-cell contact?

Transformation

Cloning

Transduction

Conjugation (correct)

What type of phage can transfer any genes during the transduction process?

Lysogenic phage

Generalized phage (correct)

Temperate phage

Virulent phage

Which of the following statements about natural transformation is true?

Only plasmid DNA can be taken up by the recipient cell.

One strand of donor DNA is destroyed while the other is incorporated. (correct)

It involves the incorporation of RNA from donor cells.

Recipient cells must be in a vegetative state for transformation to occur.

In recombinant DNA technology, what is the primary purpose of restriction endonucleases?

To recognize and cleave specific DNA sequences Signup and view all the answers

What defines a high frequency recombinant (HFR) cell?

A cell that has integrated plasmid into its chromosome Signup and view all the answers

Which application is NOT commonly associated with recombinant DNA technology?

Therapeutic cloning of embryos Signup and view all the answers

Which of the following statements accurately describes plasmids?

They are primarily involved in bacterial genetic engineering. Signup and view all the answers

During which stage of a bacteriophage life cycle does an error in excision lead to the transfer of specific chromosomal genes?

Lysogenic cycle Signup and view all the answers

Which type of gene therapy aims to inhibit the expression of specific genes?

Inhibitory gene therapy Signup and view all the answers

What is the primary purpose of gene therapy?

To change the expression of a person's genes Signup and view all the answers

What distinguishes opportunistic pathogens from commensal organisms?

Opportunistic pathogens can cause disease under certain conditions. Signup and view all the answers

Which of the following correctly defines pathogenicity?

The process of disease initiation Signup and view all the answers

What is the primary role of RNA polymerase during transcription?

To catalyze the formation of mRNA from chromosomal DNA Signup and view all the answers

Which situation exemplifies when a commensal organism acts as an opportunistic pathogen?

Streptococcus viridans causing endocarditis after dental work Signup and view all the answers

Which of the following accurately describes plasmids?

Plasmids are small circular DNA molecules that replicate autonomously Signup and view all the answers

How does the synthesis of the lagging strand occur during DNA replication?

Fragmented into Okazaki fragments requiring multiple initiations Signup and view all the answers

Which among these is considered a source of infection that is NOT living?

Soil and water Signup and view all the answers

How do carriers pose a higher risk than infected patients?

They can spread the pathogen without exhibiting signs of illness. Signup and view all the answers

Which step is NOT involved in the gene expression process?

Replication of plasmids within the cell Signup and view all the answers

Which transmission route involves the direct spread of pathogens through respiratory droplets?

Direct respiratory spread Signup and view all the answers

What is the main purpose of transposons in bacterial genetics?

To enable the movement of genetic material within the genome Signup and view all the answers

What characterizes the stationary phase of bacterial growth?

Equal rates of division and death leading to a stable population size Signup and view all the answers

Which component is NOT part of the bacterial genome?

RNA sequences Signup and view all the answers

What initiates the process of translation in bacteria?

The recognition of the start codon by the 30S subunit Signup and view all the answers

Study Notes

Microbial Classification

Microorganisms are divided into eukaryotes, which contain a membrane-bound nucleus, and prokaryotes, which do not.
Eukaryotic cells have a true nucleus with a nucleolus and nuclear membrane. Prokaryotic cells have a premature nucleus without a nucleolus or nuclear membrane.
Eukaryotic chromosomes are more than one. Prokaryotic chromosomes are a single, double-stranded DNA molecule.
Eukaryotic cytoplasmic membranes contain sterols. Prokaryotic cytoplasmic membranes generally do not contain sterols, except in mycoplasmas.
Eukaryotes have 80S ribosomes. Prokaryotes have 70S ribosomes.
Eukaryotic respiratory systems are located in mitochondria. Prokaryotic respiratory systems are located in the cytoplasmic membrane.
Eukaryotes multiply by mitosis. Prokaryotes multiply by binary fission.
Examples of eukaryotes include fungi. Examples of prokaryotes include bacteria and rickettsia.

Morphology of the Bacterial Cell

Bacteria are small, unicellular prokaryotic organisms with rigid cell walls.
They multiply by simple binary fission.
Gram staining divides bacteria into two groups: Gram-positive and Gram-negative.
- Gram-positive bacteria resist decolorization by alcohol, appearing violet under a microscope.
- Gram-negative bacteria are decolorized by alcohol, appearing red under a microscope.
Bacterial cell walls have a peptidoglycan layer.
- Gram-positive cell walls have a thick peptidoglycan layer (50-60% of the cell wall). They often have teichoic acid.
- Gram-negative cell walls have a thin peptidoglycan layer (5-10% of the cell wall). They have an outer membrane, lipopolysaccharide layer, and periplasmic space.

Morphology of Bacterial Cell: Cell Wall Components

Gram-positive cell wall:
- Peptidoglycan layer: 50-60% of the cell wall thickness.
- Teichoic acid: Antigenic structure.
Gram-negative cell wall:
- Peptidoglycan layer: 5-10% of the cell wall thickness
- Lipoprotein layer
- Outer membrane: outside the lipoprotein layer.
- Lipopolysaccharide (LPS) layer: endotoxin (lipid A) + polysaccharide O antigen
- Periplasmic space

Function of Bacterial Cell Wall

Preservation of cell shape (rigidity)
Osmotic sensitivity.
Antigenicity
Toxicity (LPS in Gram-negative bacteria).
Target for antibiotics (e.g., penicillin and cephalosporins).

Morphology of Bacterial Cell: Other Components

Cytoplasmic membrane (Plasma membrane):
- Semi-permeable, double layered structure. Composed of phospholipids and proteins.
Function: Selective permeability and active transport; energy production, site of respiration; excretion of pathogenic proteins and toxins.
Mesosome: Irregular, convoluted invagination of cytoplasmic membrane; sites of respiratory enzymes; increased membrane surface area; involvement in cell division.

The Bacterial Genome

Nuclear body: DNA concentrated in the cytoplasm within a nucleoid; lacks a nuclear membrane or nucleolus.
Plasmid: Extra-chromosomal DNA molecule.
Ribosomes: 70S; comprised of 30S and 50S subunits. Protein synthesis.
Target of antibiotics: Tetracycline and chloramphenicol.

Extracellular Structures and Appendages

Capsule: Polysaccharide layer (in most bacteria but not Bacillus anthracis which is polypeptide). Virulence factor against phagocytosis; antigenic properties; adherence of bacteria to tissues.
Flagella: Filamentous appendages enabling movement; motility; antigenicity.
Pili (fimbriae): Short, hair-like appendages; adhesion; virulence factors; important in bacterial identification (antigenic).

Bacterial Endospores

Highly resistant, resting structures.
Formed by some Gram-positive bacilli in adverse environmental conditions (depletion of nutrients, heat, dryness etc).
Core with essential enzymes and thick peptidoglycan cortex (spore coat).
Resistant to heat, chemicals, and radiation.
Important medically due to resistance to heating and need to sterilize materials by autoclaving.
Can be used for contamination testing in wounds or soil samples.

Bacterial Growth Requirements

Bacterial growth is increase in cell mass.
Nutrition
- Autotrophic: Utilize inorganic sources of carbon and nitrogen.
- Heterotrophic: Require organic carbon and nitrogen sources (like sugar and proteins).
Gaseous requirements (e.g. Oxygen)
- Strict aerobic: Require oxygen for metabolism

Bacterial Products

Endopigments: Localized in the bacteria; color the bacterial colonies (e.g., staphylococcus aureus is golden).
Exopigments: Diffuse out of bacteria into surrounding medium; color the medium e.g., pseudomonas is greenish blue; some have roles in bacterial respiration

Bacterial Toxins

Exotoxins: Diffusible toxins; protein nature; highly toxic; strong antigenic specificity (target specific cells and tissues); heat labile.
Endotoxins: Bound to the body and released only when the organism disintegrates; lipopolysaccharide nature; less toxic; weak antigenic specificity (non-specific); heat stable

Bacterial Growth and Reproduction

Bacterial Growth = increase in number via asexual binary fission.
The bacterial growth curve has lag, log (exponential), stationary and death (decline) phases.
Lag, exponential, stationary and death phases have different properties depending on characteristics like type of organism, initial inoculum size, and medium.

Bacterial Genetics

Bacteria are convenient for genetic studies due to haploid nature, rapid growth, and large numbers.
Chromosome: major DNA molecule; circular.
Extra-chromosomal DNA: Plasmid; circular DNA molecule capable of autonomous replication; often carries non-essential genes; can be transferred between cells; may confer virulence or antibiotic resistance.
Transposons: Jumping genetic elements; can move between different locations within the genome; carry genes for antibiotic resistance and other traits. Can also cause mutations.

Bacteriophages

Bacteriophage: Virus that infects bacteria; lytic cycle or lysogenic cycle; can be used in research and treatment.

Antimicrobial Chemotherapy

Bactericidal drugs: rapid killing of bacteria; irreversible; examples are penicillin, cephalosporins and aminoglycosides.
Bacteriostatic drugs: inhibit bacterial multiplication; reversible; host's immune system is required to eliminate the bacteria; includes sulfonamides, tetracyclines and chloramphenicol.
Mechanisms of action: Inhibition of bacterial cell wall synthesis, cytoplasmic membrane functions, protein synthesis, nucleic acid synthesis; competitive inhibition.

Resistance to Antimicrobial Agents

Several mechanisms lead to resistance: inactivation of enzyme by production; alteration of permeability to drug; alteration of target, alteration metabolic pathway, and alteration of enzyme.

Pathogenicity and Infectious Disease

Pathogenicity: ability of organism to cause disease.
Virulence: degree of pathogenicity.
Infection: multiplication of infectious agent within body, may be inapparent or asymptomatic.
Disease: development of signs and symptoms of disease.
Sources of infection: human, animal, or inanimate sources (e.g., soil).
Transmission: direct (contact, spread of large droplets), indirect (vector borne, airborne), or through inanimate sources.

Antimicrobial prophylaxis

Prophylaxis: Measures to prevent infection in situations where risk of infection is high.
Combining antimicrobial drugs can be synergistic, allowing for more effective treatment or to prevent the rapid development of antibiotic resistance.

Genetic Engineering and Recombinant DNA Technology

Recombinant DNA technology is used to isolate genes, create new combinations, and clone genes using vectors (e.g. plasmids or bacteriophages). This has numerous applications including, vaccine production, production of essential proteins and molecular diagnosis.

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Description

Test your knowledge on gene transfer mechanisms in microbiology with this quiz. It covers key concepts, including transformation, transduction, and recombinant DNA technology. Understand the processes that enable genetic recombination and the implications for gene therapy.