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Questions and Answers
A bacterium contains a plasmid with a gene conferring resistance to ampicillin. If this bacterium readily transfers this plasmid to other bacteria through direct contact, what type of plasmid is likely responsible?
A bacterium contains a plasmid with a gene conferring resistance to ampicillin. If this bacterium readily transfers this plasmid to other bacteria through direct contact, what type of plasmid is likely responsible?
- Artificial Plasmid
- Stringent Plasmid
- Incompatible Plasmid
- Conjugative Plasmid (correct)
Which of the following characteristics is unique to eukaryotic DNA replication when compared to prokaryotic DNA replication?
Which of the following characteristics is unique to eukaryotic DNA replication when compared to prokaryotic DNA replication?
- Replication occurs continuously.
- Only two DNA polymerases are involved.
- Replication starts at a single origin.
- Replication occurs in the nucleus. (correct)
A scientist isolates a plasmid from a bacterial strain and determines it can replicate in both E. coli and Saccharomyces cerevisiae (yeast). How would you classify this plasmid?
A scientist isolates a plasmid from a bacterial strain and determines it can replicate in both E. coli and Saccharomyces cerevisiae (yeast). How would you classify this plasmid?
- Conjugative plasmid
- Stringent plasmid
- Shuttle vector (correct)
- Incompatible plasmid
Which statement accurately describes the organization of genes on prokaryotic mRNA compared to eukaryotic mRNA?
Which statement accurately describes the organization of genes on prokaryotic mRNA compared to eukaryotic mRNA?
A researcher discovers a new mobile genetic element in a bacterial genome. This element consists of a central region encoding a tetracycline resistance gene flanked by two identical insertion sequences (IS). How should this element be classified?
A researcher discovers a new mobile genetic element in a bacterial genome. This element consists of a central region encoding a tetracycline resistance gene flanked by two identical insertion sequences (IS). How should this element be classified?
Which of the following is a key difference between Type I and Type II topoisomerases?
Which of the following is a key difference between Type I and Type II topoisomerases?
A bacterial strain exhibits increased resistance to multiple antibiotics after acquiring a mobile genetic element. If this element encodes only proteins necessary for its own transposition, and includes direct or inverted repeats at its ends, what is its most likely identity?
A bacterial strain exhibits increased resistance to multiple antibiotics after acquiring a mobile genetic element. If this element encodes only proteins necessary for its own transposition, and includes direct or inverted repeats at its ends, what is its most likely identity?
Which of the following characteristics is LEAST likely to be associated with plasmids?
Which of the following characteristics is LEAST likely to be associated with plasmids?
What is a key function encoded by some plasmids that contributes to bacterial pathogenicity?
What is a key function encoded by some plasmids that contributes to bacterial pathogenicity?
A researcher is studying DNA replication in a newly discovered bacterium. They observe that DNA replication proceeds bidirectionally from a single origin. Which of the following enzymes would be essential in this process to relieve the torsional stress ahead of the replication fork?
A researcher is studying DNA replication in a newly discovered bacterium. They observe that DNA replication proceeds bidirectionally from a single origin. Which of the following enzymes would be essential in this process to relieve the torsional stress ahead of the replication fork?
What is the primary factor differentiating compatible and incompatible plasmids within a bacterial cell?
What is the primary factor differentiating compatible and incompatible plasmids within a bacterial cell?
Which of the following RNA types is common to both prokaryotic and eukaryotic organisms?
Which of the following RNA types is common to both prokaryotic and eukaryotic organisms?
A researcher introduces a plasmid into a bacterial cell, creating an artificial plasmid. What modification is most likely implemented by the researcher in creating this artificial plasmid?
A researcher introduces a plasmid into a bacterial cell, creating an artificial plasmid. What modification is most likely implemented by the researcher in creating this artificial plasmid?
Which description accurately portrays the structure of a non-composite transposon?
Which description accurately portrays the structure of a non-composite transposon?
A narrow host range plasmid is MOST likely to:
A narrow host range plasmid is MOST likely to:
Why might a semi-circular plasmid be considered a transient form?
Why might a semi-circular plasmid be considered a transient form?
Which of the following features distinguishes prokaryotic genomes from eukaryotic genomes?
Which of the following features distinguishes prokaryotic genomes from eukaryotic genomes?
In bacterial DNA replication, what is the function of DNA gyrase (Topoisomerase II) in managing the bacterial chromosome's structure?
In bacterial DNA replication, what is the function of DNA gyrase (Topoisomerase II) in managing the bacterial chromosome's structure?
How do stringent plasmids differ from high copy number plasmids, regarding their replication within a bacterial cell?
How do stringent plasmids differ from high copy number plasmids, regarding their replication within a bacterial cell?
A bacterium acquires a transposon that inserts within a gene essential for cell wall synthesis. What is the most likely outcome for the bacterium?
A bacterium acquires a transposon that inserts within a gene essential for cell wall synthesis. What is the most likely outcome for the bacterium?
Flashcards
What is a genome?
What is a genome?
The total genetic information in an organism.
Prokaryotic Genome
Prokaryotic Genome
A single, circular DNA molecule; prokaryotes have a single copy of each gene.
DNA: Prokaryotes vs. Eukaryotes
DNA: Prokaryotes vs. Eukaryotes
Prokaryotes: Single, circular DNA in cytoplasm. Eukaryotes: multiple, linear DNA in nucleus; bound to histones.
mRNA: Prokaryotes vs. Eukaryotes
mRNA: Prokaryotes vs. Eukaryotes
mRNA in prokaryotes are polycistronic, in eukaryotes are monocistronic.
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DNA Replication: Prokaryotes vs. Eukaryotes
DNA Replication: Prokaryotes vs. Eukaryotes
Prokaryotes: Continuous, single origin. Eukaryotes: S phase, multiple origins.
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Transcription: Prokaryotes vs. Eukaryotes
Transcription: Prokaryotes vs. Eukaryotes
Prokaryotes: in cytoplasm, one type of RNA Polymerase. Eukaryotes: in nucleus, at least three types.
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Extrachromosomal Elements
Extrachromosomal Elements
All DNA material present in a cell other than chromosomal DNA.
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What are Plasmids?
What are Plasmids?
DNA pieces separate from the chromosome, contain an origin of replication, and replicate independently.
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Compatible Plasmids
Compatible Plasmids
Cell can maintain more than one plasmid if different replication origins.
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Incompatible Plasmids
Incompatible Plasmids
Inability of plasmids to be maintained in the same cell, same replication origin.
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Broad Host Range Plasmids
Broad Host Range Plasmids
Can replicate in a wide range of bacteria.
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Narrow Host Range Plasmids
Narrow Host Range Plasmids
Only replicate in one or few closely related bacteria.
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Conjugative Plasmids
Conjugative Plasmids
Can mobilize from one cell to another by conjugation (have tra genes).
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Shuttle Vector
Shuttle Vector
Plasmids which propagate in two different host species (yeast and bacteria).
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Natural Plasmids
Natural Plasmids
Present in bacterial and some yeast cells; F- plasmid (F-pili during conjugation).
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Artificial Plasmids
Artificial Plasmids
Designed artificially, include antibiotic resistant markers/DNA sequence for restriction.
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Importance of Plasmids
Importance of Plasmids
Resistance to antibiotics, heavy metals, and UV; conjugation; toxins, enzymes production.
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What are Transposons?
What are Transposons?
Extrachromosomal DNA capable of moving from one location in DNA to another.
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Insertion Sequence (IS)
Insertion Sequence (IS)
Encode only proteins needed for transposition; carry same repeats at their ends.
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Composite Transposons
Composite Transposons
Contain 2 IS at both ends and a piece of DNA for antibiotic resistance or virulence.
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- The module is Foundations of Infections & Infestations BMS171, for level 1, semester 2.
- The instructor is Professor Doctor Mohammed Mahmoud El-Naggar, from the Department of Medical Microbiology and Immunology; can be reached via mohammedelnaggar41@yahoo.com or 01126625177; available Sundays 10:00-12:00 AM.
Learning Outcomes
- Students will be able to describe the bacterial genome and identify differences between prokaryotic and eukaryotic DNA and RNA.
- Students will be able to compare and contrast between prokaryotes and eukaryotes in DNA replication, transcription, and translation.
- Students will be able to identify extra-chromosomal elements, classify different types of plasmids, and define/describe the structure of transposons.
Lecture Outline
- Prokaryotic and eukaryotic DNA and mRNA structure, DNA replication, transcription, and translation are different.
- Bacterial Extra-chromosomal elements include plasmids and transposons.
Clinical Correlation
- A 9-year-old girl has a sore throat, cough, hoarseness, fever.
- Isolated throat pain, no rhinorrhea, sinus pressure, or headache; treated with low-dose ampicillin.
- She does not respond to ampicillin.
Genome
- This refers to the total genetic information in an organism.
- The prokaryotic genome (bacterial) consists of a single copy (haploid) circular DNA molecule ranging from 580-4600 Kbp.
- Many bacteria contain extra chromosomal DNA materials called plasmids and transposons.
Prokaryotic vs. Eukaryotic DNA
| Feature | Prokaryotes | Eukaryotes |
|---|---|---|
| Number of Copies | Single copy (haploid) | 2 copies (diploid) |
| Shape | Circular | Linear |
| Location | Cytoplasm (nucleoid) | Within a nucleus |
| Histones | No | Bound to histone proteins |
| Repetitive DNA & Introns | Little repetitive DNA, no introns | Large amounts of repetitive DNA and introns |
| Extrachromosomal Elements | Present | Absent |
RNA
- Three main classes of RNA molecules exist.
- Messenger RNA (mRNA)
- Transfer RNA (tRNA)
- Ribosomal RNA (rRNA)
Prokaryotic vs. Eukaryotic mRNA
| Feature | Prokaryotes | Eukaryotes |
|---|---|---|
| Number Encoded Proteins | Polygenic/poly-cistronic | Monogenic/mono-cistronic |
| Beginning of Translation | During transcription | Transported to cytoplasm first |
| Lifespan | Very short (constant breakdown) | Much longer (stable) |
| Post Transcriptional Modifications | Minor | Major: Polyadenylation, capping, splicing |
Prokaryotic vs. Eukaryotic DNA Replication
| Feature | Prokaryotes | Eukaryotes |
|---|---|---|
| Time | Continuous | During S phase |
| Location | Cytoplasm | Nucleus |
| Origin | Single point (Ori C) | Multiple points |
| Direction | Bidirectional | Unidirectional |
| DNA Polymerases | 2 | 4 or more |
| Topoisomerases | Type II (DNA gyrase) | Type I |
| Okazaki Fragments | Longer | Shorter |
| Termination | Single site | Several sites |
Transcription
- RNA Polymerase exists in one type in prokaryotes and three types in eukaryotes.
- Location is the cytoplasm in prokaryotes and the nucleus in eukaryotes.
- Post transcription modification is minor in prokaryotes and Major in eukaryotes.
- It occurs simultaneously in prokaryotes; transcription occurs before translation in eukaryotes.
- Promoters consist of three different elements in prokaryotes and many different elements in eukaryotes.
- Nascent RNA introns are absent in prokaryotes and present in eukaryotes.
Extrachromosomal Elements
- DNA material present in a cell other than chromosomal DNA.
- Plasmids
- Transposons
- Bacteriophages (viruses infecting bacteria)
Plasmids
- These are pieces of DNA existing separately from the chromosome.
- They contain an origin of replication.
- They replicate independently from the chromosome.
Plasmids Classification
- Size: Few hundred base pairs up to 3000 Kb.
- Copy Number:
- Stringent: 1-2 copies/cell.
- Low copy number: 10-15 copies/cell.
- High copy number: Up to 50 copies/cell.
- Extremely high copy number: Up to 100-200 copies/cell.
- Compatibility:
- Compatible: Cell maintains multiple plasmids with different replication origins.
- Incompatible: Two plasmids cannot be maintained due to the same replication origin.
- Shape:
- Covalently closed circular (CCC): Most common, double-stranded, completely closed.
- Semi-circular: Transient, one strand closed, the other opened.
- Linear: Double-stranded, unstable, attacked by exonucleases.
- Host Range:
- Broad: Replicates in a wide range of bacteria.
- Narrow: Replicates in one or a few closely related bacteria.
- Moving Plasmids from cell to cell:
- Conjugative: Mobilize via conjugation (tra genes).
- Non-conjugative: Cannot be mobilized.
- Shuttle vector: Propagate in two different host species (yeast and bacteria).
- Artificial and Natural Plasmids:
- Natural: Present naturally in bacterial and some yeast cells.
- Artificial: Designed artificially.
- Adding antibiotic-resistant markers or a DNA sequence to be targeted for restriction endonucleases,
- Used as vectors in gene cloning.
Importance of Plasmids
- Encode gene products responsible for:
- Resistance to antibiotics, heavy metals (metal reductase), and UV (DNA repair enzymes)
- Conjugation
- Production of toxins, enzymes, and bacteriocins
- Biochemical reactions like sugar fermentation
- They act as a vector in molecular biology for gene therapy and DNA vaccines.
Transposons
- Extra chromosomal small pieces of DNA
- They're capable of moving themselves from one location to another (movable elements or jumping genes).
- Structure:
- Insertion Sequence (IS)
- Composite Transposons (Tn)
- Non-composite Transposons
Insertion Sequence (IS)
- Simplest form
- Encode only proteins needed for its transposition
- Carry the same repeats at their ends (direct or inverted)
- Examples: IS 1, 3, and 10
Composite Transposons
- Contain 2 IS at both ends and a central piece of DNA
- Encode for antibiotic resistance or virulence factors
- Tn5 encodes for kanamycin resistance.
- Tn10 encodes for tetracycline resistance.
Non-Composite Transposons
- They have no IS at their ends.
- Encode for transposition proteins.
- Carry genes for antibiotic resistance, virulence factors, and catabolic enzymes.
- Tn3 carries an ampicillin resistance gene.
- Tn7 carries genes for streptomycin and trimethoprim resistance.
Quick Questions
- Why does the girl not respond to ampicillin?
- Which of the following plasmids are stringent plasmids?
- d. Plasmids that present as one or two copies inside the cell.
- Prokaryotic DNA is characterized by:
- d. No introns
- Extrachromosomal small piece of DNA capable of moving from one location in DNA to another:
- c. Transposon.
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