Podcast
Questions and Answers
Which of the following is a key difference between prokaryotic and eukaryotic genomes regarding extra-chromosomal elements?
Which of the following is a key difference between prokaryotic and eukaryotic genomes regarding extra-chromosomal elements?
- Prokaryotic genomes may contain plasmids, while eukaryotic genomes typically do not. (correct)
- Eukaryotic genomes contain plasmids, while prokaryotic genomes do not.
- Both prokaryotic and eukaryotic genomes equally rely on plasmids for genetic diversity.
- Neither prokaryotic nor eukaryotic genomes contain extra-chromosomal elements.
A bacterium is found to have a mutation that significantly reduces the activity of DNA gyrase. What aspect of DNA replication would be most directly affected by this mutation?
A bacterium is found to have a mutation that significantly reduces the activity of DNA gyrase. What aspect of DNA replication would be most directly affected by this mutation?
- The proofreading ability of the DNA polymerase.
- The rate of elongation during replication.
- The separation of DNA strands ahead of the replication fork. (correct)
- The synthesis of Okazaki fragments.
Which of the following characteristics is associated with prokaryotic mRNA, but not eukaryotic mRNA?
Which of the following characteristics is associated with prokaryotic mRNA, but not eukaryotic mRNA?
- Involvement in protein synthesis
- Monogenic structure
- Polygenic structure (correct)
- Requirement for translation
A researcher is studying a newly discovered bacterial species and observes that its DNA replication starts at a single point. Which of the following is most likely true about this species' DNA replication process?
A researcher is studying a newly discovered bacterial species and observes that its DNA replication starts at a single point. Which of the following is most likely true about this species' DNA replication process?
Which of the following features distinguishes Type I topoisomerases from Type II topoisomerases?
Which of the following features distinguishes Type I topoisomerases from Type II topoisomerases?
A bacterial strain is found to have a mutation that affects the post-transcriptional modification of mRNA. Which process is most likely to be disrupted in this bacterial strain?
A bacterial strain is found to have a mutation that affects the post-transcriptional modification of mRNA. Which process is most likely to be disrupted in this bacterial strain?
A researcher discovers a new plasmid in bacteria that can be transferred from one cell to another through conjugation. What genetic element must be present on this plasmid?
A researcher discovers a new plasmid in bacteria that can be transferred from one cell to another through conjugation. What genetic element must be present on this plasmid?
Which of the following correctly describes the function of plasmids in bacterial cells?
Which of the following correctly describes the function of plasmids in bacterial cells?
A microbiology student is studying bacterial ribosomes. Which of the following is a key difference between prokaryotic and eukaryotic ribosomes?
A microbiology student is studying bacterial ribosomes. Which of the following is a key difference between prokaryotic and eukaryotic ribosomes?
A bacterium contains a plasmid with a high copy number. Which statement best describes this plasmid?
A bacterium contains a plasmid with a high copy number. Which statement best describes this plasmid?
Suppose a bacterial cell contains two different plasmids. One is a compatible plasmid and other is an incompatible plasmid. What determines whether the two plasmids can coexist stably within the same cell?
Suppose a bacterial cell contains two different plasmids. One is a compatible plasmid and other is an incompatible plasmid. What determines whether the two plasmids can coexist stably within the same cell?
What role do plasmids play in bacterial resistance to antibiotics and heavy metals?
What role do plasmids play in bacterial resistance to antibiotics and heavy metals?
Which of the following best describes the key characteristic of transposons?
Which of the following best describes the key characteristic of transposons?
What is the primary function of the proteins encoded by an insertion sequence (IS) element?
What is the primary function of the proteins encoded by an insertion sequence (IS) element?
Which of the following is present in composite transposons, but not in non-composite transposons?
Which of the following is present in composite transposons, but not in non-composite transposons?
Unlike eukaryotic genomes, prokaryotic genomes lack which of the following features?
Unlike eukaryotic genomes, prokaryotic genomes lack which of the following features?
A bacterial species exhibits a mutation that disables its DNA gyrase enzyme. Which of the following cellular processes would be LEAST directly affected?
A bacterial species exhibits a mutation that disables its DNA gyrase enzyme. Which of the following cellular processes would be LEAST directly affected?
Which of the following is a distinguishing characteristic of eukaryotic mRNA processing that is absent in prokaryotes?
Which of the following is a distinguishing characteristic of eukaryotic mRNA processing that is absent in prokaryotes?
During DNA replication in prokaryotes, the function of the enzyme DNA gyrase is essential for which of the following processes?
During DNA replication in prokaryotes, the function of the enzyme DNA gyrase is essential for which of the following processes?
A bacterial cell is treated with a drug that inhibits the activity of bacterial topoisomerases. Which cellular process would be most directly affected?
A bacterial cell is treated with a drug that inhibits the activity of bacterial topoisomerases. Which cellular process would be most directly affected?
Which type of post-transcriptional modification plays a crucial role in the stability and translatability of eukaryotic mRNA but is largely absent in prokaryotic mRNA?
Which type of post-transcriptional modification plays a crucial role in the stability and translatability of eukaryotic mRNA but is largely absent in prokaryotic mRNA?
A bacterial plasmid is engineered to contain a multiple cloning site (MCS) flanked by strong, inducible promoters and a selectable marker. What is the primary purpose of the MCS in this context?
A bacterial plasmid is engineered to contain a multiple cloning site (MCS) flanked by strong, inducible promoters and a selectable marker. What is the primary purpose of the MCS in this context?
A research team discovers a new bacterial plasmid that confers resistance to multiple antibiotics and heavy metals. What genetic mechanism likely contributes the MOST to the rapid spread of this resistance among different bacterial species?
A research team discovers a new bacterial plasmid that confers resistance to multiple antibiotics and heavy metals. What genetic mechanism likely contributes the MOST to the rapid spread of this resistance among different bacterial species?
Which of the following features distinguishes prokaryotic ribosomes from their eukaryotic counterparts?
Which of the following features distinguishes prokaryotic ribosomes from their eukaryotic counterparts?
A bacterial strain is found to harbor a plasmid with a mutation that significantly reduces its copy number. What is the MOST likely consequence of this mutation?
A bacterial strain is found to harbor a plasmid with a mutation that significantly reduces its copy number. What is the MOST likely consequence of this mutation?
Two plasmids in a bacterial cell share a similar replication origin and mechanism, yet one plasmid is maintained at a high copy number while the other gradually disappears. Which phenomenon BEST explains this observation?
Two plasmids in a bacterial cell share a similar replication origin and mechanism, yet one plasmid is maintained at a high copy number while the other gradually disappears. Which phenomenon BEST explains this observation?
A bacterium is exposed to a novel antibiotic. Subsequent analysis reveals that the bacterium expresses a plasmid-borne gene encoding an enzyme that modifies the antibiotic, rendering it inactive. Which of the following mechanisms BEST explains this resistance?
A bacterium is exposed to a novel antibiotic. Subsequent analysis reveals that the bacterium expresses a plasmid-borne gene encoding an enzyme that modifies the antibiotic, rendering it inactive. Which of the following mechanisms BEST explains this resistance?
What is the MOST significant implication of transposons' ability to insert themselves into different locations within a genome?
What is the MOST significant implication of transposons' ability to insert themselves into different locations within a genome?
What distinguishes composite transposons from insertion sequences (IS) elements?
What distinguishes composite transposons from insertion sequences (IS) elements?
A bacterial strain contains a transposon inserted within a gene essential for cell wall synthesis. The transposon consists of an insertion sequence (IS) element flanked by two copies of a resistance gene. What event is MOST likely to occur if this transposon undergoes another round of transposition?
A bacterial strain contains a transposon inserted within a gene essential for cell wall synthesis. The transposon consists of an insertion sequence (IS) element flanked by two copies of a resistance gene. What event is MOST likely to occur if this transposon undergoes another round of transposition?
Flashcards
Genome
Genome
The total genetic information in an organism.
Prokaryotic Genome (Bacterial)
Prokaryotic Genome (Bacterial)
A single copy (haploid) circular DNA molecule found in bacterial genomes.
RNA molecules
RNA molecules
Messenger RNA, Transfer RNA, and Ribosomal RNA
Beginning of mRNA Translation (Eukaryotes)
Beginning of mRNA Translation (Eukaryotes)
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Plasmids
Plasmids
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Compatible Plasmids
Compatible Plasmids
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Transposons
Transposons
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Composite Transposons
Composite Transposons
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Beginning of mRNA translation in eukaryotes
Beginning of mRNA translation in eukaryotes
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Extra-Chromosomal elements.
Extra-Chromosomal elements.
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Semicircular Form (Plasmids)
Semicircular Form (Plasmids)
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Shuttle vector
Shuttle vector
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Broad Host Range Plasmids
Broad Host Range Plasmids
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Non-composite Transposons
Non-composite Transposons
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Bacterial genome copies
Bacterial genome copies
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Eukaryotic Genome Location
Eukaryotic Genome Location
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Prokaryotic mRNA
Prokaryotic mRNA
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Eukaryotes
Eukaryotes
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Relation to translation in prokaryotes
Relation to translation in prokaryotes
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CCC form
CCC form
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Linear Form (Plasmids)
Linear Form (Plasmids)
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Conjugative Plasmids
Conjugative Plasmids
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High copy plasmid
High copy plasmid
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Artifical Plasmids
Artifical Plasmids
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Narrow host range
Narrow host range
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Study Notes
- The lecture covers bacterial chromosomal and extra-chromosomal elements for a level 1, semester 2 microbiology course (PPPM), instructed by Dr. Ziad Mahana.
Genome
- The genome is the total genetic information in an organism.
- Prokaryotic genomes consist of a single, haploid, circular DNA molecule.
- Prokaryotic genome size ranges from 580-4600 Kbp.
- Bacteria may have extra-chromosomal DNA like plasmids and transposons.
Prokaryotic vs. Eukaryotic Genomes
- Prokaryotic genomes have a single, haploid copy, while eukaryotic genomes have two diploid copies.
- Prokaryotic DNA is circular; eukaryotic DNA is linear.
- Prokaryotic DNA is located freely in the cytoplasm (within the nucleoid), while eukaryotic DNA is within a nucleus.
- Prokaryotic DNA lacks histones (naked DNA), whereas eukaryotic DNA is bound to histone proteins.
- Prokaryotic DNA has little repetitive DNA and no introns; eukaryotic DNA contains large amounts of repetitive DNA and introns.
- Prokaryotes may have extra-chromosomal plasmids, which are absent in eukaryotes.
RNA
- The three main classes of RNA molecules are messenger RNA (mRNA), transfer RNA (tRNA), and ribosomal RNA (rRNA).
Prokaryotic vs. Eukaryotic mRNA
- Prokaryotic mRNA is polygenic/poly-cistronic, coding for multiple proteins.
- Eukaryotic mRNA is monogenic/mono-cistronic, coding for only one protein.
- In prokaryotes, mRNA translation begins during transcription.
- In eukaryotes mRNA is transported to the cytoplasm before translation starts.
- Prokaryotic mRNA has a short life span due to rapid breakdown by nucleases.
- Eukaryotic mRNA is much more stable, with a longer life span.
- Prokaryotic mRNA undergoes minor post-transcriptional modifications.
- Eukaryotic mRNA undergoes major modifications like polyadenylation, capping, and splicing.
Prokaryotic vs. Eukaryotic DNA Replication
- Prokaryotic DNA replication is continuous.
- Eukaryotic DNA replication occurs during the S phase of the cell cycle.
- Prokaryotic DNA replication occurs in the cytoplasm.
- Eukaryotic DNA replication occurs in the nucleus.
- Prokaryotic DNA replication starts at one point (Ori C).
- Eukaryotic DNA replication starts at multiple points.
- Prokaryotic DNA replication is bidirectional, proceeding in two opposing directions.
- Eukaryotic DNA replication is unidirectional.
- Prokaryotes have two DNA polymerases.
- Eukaryotes have four or more DNA polymerases.
- Prokaryotic DNA replication is faster than eukaryotic.
- Prokaryotes use type II topoisomerase/DNA gyrase to cut both DNA strands
- Eukaryotes use type I topoisomerases to cut a single strand of DNA.
- Okazaki fragments are longer in prokaryotes and shorter in eukaryotes.
- Prokaryotes have a single termination site midway in the circular chromosome.
- To halt the replication process, the two replication forks meet at the termination site.
- Eukaryotes have several termination sites.
- Type I topoisomerases create a nick in one strand of DNA, pass the intact strand through, and reseal the gap.
- Type II topoisomerases create a double-stranded break in the DNA, forming a gate for another segment of the helix.
Prokaryotic vs. Eukaryotic Transcription
- Prokaryotes have one type of RNA polymerase.
- Eukaryotes have three types of RNA polymerase.
- Prokaryotic transcription occurs in the cytoplasm.
- Eukaryotic transcription occurs in the nucleus.
- Prokaryotes have minor post-transcription modifications; eukaryotes have major modifications.
- Prokaryotic translation occurs simultaneously with transcription.
- With eukaryotes, transcription precedes translation, RNA is first transcribed in the nucleus and then translated in the cytoplasm.
- Prokaryotes have three promoter elements.
- Eukaryotes have many different promoter elements.
- Nascent RNA lacks introns in prokaryotes but contains them in eukaryotes.
Prokaryotic vs. Eukaryotic Translation
- Prokaryotic translation is very rapid (350-400 aa/min).
- Eukaryotic translation is slower (50 aa/min).
- Prokaryotic transcription and translation are coupled
- Eukaryotic processes are uncoupled.
- Prokaryotic ribosomes are 70S (30S + 50S).
- Eukaryotic ribosomes are 80S (40S + 60S).
- Prokaryotes use formylmethionyl-tRNA and three initiation factors.
- Eukaryotes use methionyl-tRNA and more than three initiation factors.
- Protein folding in prokaryotes does not occur until the complete polypeptide chain is synthesized.
- Eukaryotic protein domains fold independently after being synthesized by the ribosome.
Extra-Chromosomal Elements
- These are all DNA material present in a cell other than chromosomal DNA.
- Types of extra-chromosomal elements include plasmids, transposons, and bacteriophages (viruses infecting bacteria).
Plasmids
- Plasmids are separate pieces of DNA from the chromosome.
- Plasmids contain an origin of replication.
- Plasmids replicate independently from the chromosome.
Classification of Plasmids
- Plasmids can be classified according to size and copy number.
- Starting from a few hundred base pairs up to 3000 Kbp.
- Stringent plasmids: 1-2 copies/cell examples F-plasmid and Phage plasmid hybrid (P1).
- Low copy number plasmids: 10-15 copies/cell examples PSC 101
- High copy number plasmids: up to 50 copies/cell example is ColE, plasmid.
- Extremely high copy number plasmids: up to 100-200 copies/cell, specifically engineered.
- Plasmids are also classified by shape:
- Covalently closed circular (CCC): Most common, double strands completely closed (e.g., in E. coli).
- Semicircular: Transient, one strand is closed, the other is open.
- Linear: Double-stranded, unstable, attacked by exonucleases, present in Borrelia.
- Plasmids are grouped by Mobility:
- Conjugative plasmids: Have tra genes, mobilize plasmid from one cell to another by conjugation.
- Non-conjugative plasmids: Cannot be mobilized.
- Shuttle vector: Mobilize itself and other plasmids, propagates in two host species (Yeast & Bacteria).
- Plasmids also grouped by origin:
- Natural plasmids: Present naturally in bacteria and some yeast cells, like F-plasmid (F-pili during conjugation), carry genes for replication and functions.
- Artificial plasmids: Designed artificially, include antibiotic resistance markers or DNA sequences targetted by restriction endonucleases, used as vectors in gene cloning
- Plasmids can be classified as compatible or incompatible:
- Compatible plasmids: A cell can maintain more than one, if they carry different replication origins.
- Incompatible plasmids: A cell cannot maintain more than one, carry the same replication origin.
- Plasmids also assigned by range:
- Broad host range plasmids: replicate in a wide range of bacteria.
- Narrow host range plasmids: only replicate in one or few related bacteria.
Importance of Plasmids
- Conjugation
- Production: of toxins, enzymes, and bacteriocin
- Biochemical reactions: Sugar fermentation
- Molecular biology: as vectors, cloning vectors and therapeutic gene insertion for gene therapy.
- Confer Resistance: antibiotic resistance, heavy metal resistance (metal reductase), and UV resistance (DNA repair enzymes).
Transposons
- Transposons are extra-chromosomal DNA pieces capable of moving from one location to another in DNA (movable elements).
- There are three forms of transposable elements.
- Insertion sequence (IS): Simplest form, encodes proteins needed for transposition, carries repeated nucleotides at ends (direct or inverted repeats of 15-25 bases), examples are IS 1, 3, and 10.
- Composite transposons (Tn): Contain two IS elements at both ends, with a central piece of DNA that encodes; Antibiotic resistance & virulence factors, examples are Tn5 (kanamycin resistance) and Tn10 (tetracycline resistance).
- Non-composite transposons: Lack IS elements but encode transposition proteins, carry genes for antibiotic resistance, virulence factors, and catabolic enzymes, examples are Tn3 (ampicillin resistance gene) and Tn7 (streptomycin and trimethoprim resistance).
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