Bacterial Genetics Quiz

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Questions and Answers

What is a defining characteristic of E. Coli K12 used in bacterial genetics studies?

It has a complex genome with multiple plasmids.

It has a rough colony type and lacks adhesion factors. (correct)

It produces various toxins that influence genetic studies.

It possesses a capsule and iron-transport systems.

Which of the following researchers is NOT mentioned as a pioneer in microbial genetics?

Edward Tatum

Ester Lederberg

Barbara McClintock

James Watson (correct)

What is the role of plasmid-encoded genes in bacteria?

To encode ribosomal RNA and DNA polymerases.

To catalyze antibiotic resistance mechanisms.

To regulate the number of plasmid copies inside a cell. (correct)

To facilitate the replication of the bacterial chromosome.

What percentage of genes in bacteria are currently understood in terms of their function?

70% Signup and view all the answers

What is commonly found in plasmids but not in the bacterial genome?

Antibiotic resistance genes. Signup and view all the answers

What type of mutation typically does not change the protein's function?

Silent Signup and view all the answers

Which mutation type causes premature termination of translation?

Nonsense Signup and view all the answers

Which mutation type involves an insertion or deletion of nucleotides?

Frameshift Signup and view all the answers

What experimental approach did Esther Lederberg use to demonstrate spontaneous mutations?

Replica plating Signup and view all the answers

What is a key feature of restriction enzymes?

They recognize only palindromic sequences. Signup and view all the answers

What is the primary purpose of modification enzymes in relation to restriction enzymes?

To protect the cell's own DNA from being cut. Signup and view all the answers

In Richard Lenski's experiments with E. coli, what was observed after 75 days?

Increased fitness in cultures provided with extended generational time. Signup and view all the answers

How many times will EcoRI cut a typical bacterial genome, based on random occurrence?

It does not cut its own genome. Signup and view all the answers

Which type of mutation has the potential to change a protein's function, depending on the importance of the altered amino acid?

Missense Signup and view all the answers

What is a potential consequence of frameshift mutations?

Alterations in ribosomal reading frame affecting downstream amino acids. Signup and view all the answers

What is the primary function of transposase in transposition?

To cut and paste the element into a new location Signup and view all the answers

Which type of transposition results in the copying of an element to a new location?

Replicative transposition Signup and view all the answers

What is the purpose of a suicide vector plasmid in transposition experiments?

To disrupt functional genes in the recipient cell Signup and view all the answers

What distinguishes generalized transduction from specialized transduction?

Specialized transduction involves imperfect excision of phage DNA Signup and view all the answers

How can transduction contribute to genetic diversity in bacteria?

By facilitating the transfer of genetic material between bacteria Signup and view all the answers

What is required for both replicative and non-replicative transposition mechanisms?

Transposase and resolvase genes Signup and view all the answers

In the context of transduction, what is a transducing particle?

A virus carrying the host cell's DNA fragment Signup and view all the answers

What outcome is expected when a bacteriophage accidentally packages host DNA during generalized transduction?

Host DNA can recombine with the recipient's genome Signup and view all the answers

What is the primary reason two plasmids with similar replication controls are considered incompatible?

One will always outcompete the other. Signup and view all the answers

Which of the following best describes a prototroph?

A strain capable of making all necessary organic compounds. Signup and view all the answers

What characteristic is used to differentiate between selection and screening methods in mutant identification?

Selection allows for growth under specific conditions, while screening identifies based on phenotype. Signup and view all the answers

What type of mutation would most likely prevent a bacterium from synthesizing histidine?

Auxotrophic mutation. Signup and view all the answers

In genetic terminology, what does the genotype refer to?

The DNA sequence that causes a mutation. Signup and view all the answers

Which of the following is NOT a characteristic of a screening method in identifying mutants?

Involves the isolation of cells based on specific growth conditions. Signup and view all the answers

What would be the phenotype of a His⁻ mutant grown in the absence of histidine?

The strain would die due to lack of histidine. Signup and view all the answers

What is a notable limitation of non-selectable mutations?

Their detection requires screening a large number of colonies. Signup and view all the answers

What methodology can facilitate the screening of mutants through comparison?

Replica plating. Signup and view all the answers

How are exopolysaccharide mutants typically identified?

Through visible changes in phenotype. Signup and view all the answers

In a selection method for mutants, what kind of growth is expected for a His+ mutant on medium without histidine?

Robust growth. Signup and view all the answers

What is the primary advantage of using antibiotic selection in mutant identification?

It selectes for mutants that can survive in inhibitory conditions. Signup and view all the answers

What does the allele signify in genetic terminology?

A variant of a gene. Signup and view all the answers

In the context of mutant screening, what are auxotrophs typically selected for?

Their inability to grow in specific media. Signup and view all the answers

What is the role of EcoRI in the process of mixing DNA?

To digest DNA into fragments Signup and view all the answers

Which of the following is NOT a desirable trait for plasmid cloning vectors?

Large size Signup and view all the answers

How can researchers select for bacterial cells that carry a recombinant plasmid?

By growing them on plates containing ampicillin Signup and view all the answers

What does a clear zone around a colony on a starch plate indicate?

The colony produces the enzyme α-amylase Signup and view all the answers

Which process does transformation involve?

Direct introduction of DNA into an organism Signup and view all the answers

What is the function of ligase in the DNA mixing process?

To join DNA fragments together Signup and view all the answers

What makes shuttle vector plasmids unique?

They can replicate in multiple hosts Signup and view all the answers

What is indicated by a white colony in the X-gal system?

Insertion of DNA into the plasmid Signup and view all the answers

Which step is NOT part of the screening process for transformed cells?

Flooding a plate with acid Signup and view all the answers

What is the purpose of using the lacZ system in cloning?

To visualize successful transformation Signup and view all the answers

What do cosmids typically carry?

35-45 kb fragments Signup and view all the answers

Which of the following describes naturally competent bacteria?

They can take up naked DNA from the environment Signup and view all the answers

How do plasmids contribute to antibiotic resistance in transformed bacterial strains?

They contain genes that confer resistance Signup and view all the answers

What is the significance of cohesive end sites in phage vectors?

They allow for efficient packaging of DNA fragments Signup and view all the answers

What process allows the integration of incoming single-stranded donor DNA into the recipient's chromosome?

Recombination Signup and view all the answers

Which method has low efficiency in inducing bacterial competence?

Treatment with calcium cations Signup and view all the answers

During conjugation, what role do sex pili play?

Connect donor and recipient cells Signup and view all the answers

What is the primary purpose of using antibiotic resistance and auxotrophic markers in detecting transconjugant bacteria?

Select for successful gene transfer Signup and view all the answers

What defines specialized transduction as opposed to generalized transduction?

Carries specific host genes into transducing particles Signup and view all the answers

Which step occurs first in the process of F plasmid transfer during conjugation?

Nick made at oriT Signup and view all the answers

What is a consequence of Hfr strain DNA transfer?

High frequency of gene mapping Signup and view all the answers

What is the function of transposase enzymes in the process of transposition?

Recognize and excise transposable elements Signup and view all the answers

What occurs when an integrated F plasmid excises inaccurately?

F' plasmid carrying chromosomal genes is formed Signup and view all the answers

What happens during the process of triparental conjugation?

A donor cell transfers genes to an intermediate strain, which then donates to a recipient Signup and view all the answers

What is the role of the oriT region during the plasmid transfer process?

It is the origin of transfer for DNA during mating Signup and view all the answers

How do lytic bacteriophages contribute to generalized transduction?

By packaging host DNA accidentally Signup and view all the answers

Which of the following best describes recombination in the context of bacterial DNA transfer?

The integration of new DNA into the recipient's genome Signup and view all the answers

What is the function of insertion sequences (IS) in transposition?

Act as sites for transposon insertion Signup and view all the answers

Study Notes

Bacterial Genetics Overview

Microbial genetics emerged from microbiology, flourishing in the 1940s-1950s, and paving the way for molecular biology. Model organisms like E. coli and Salmonella typhimurium were crucial.
Key figures in microbial genetics include Barbara McClintock, Esther Lederberg, and Edward Tatum.
Currently, 70% of bacterial genes' functions are known, while the remaining 30% remain a mystery.
E. coli K12, a non-pathogenic strain, is a commonly used model organism due to its smaller genome, lack of toxins, adhesion factors, iron-transport systems, capsule, plasmids, and partial lipopolysaccharide (LPS).

Organization of Bacterial Genomes

Bacteria have a single chromosome and often plasmids, both considered replicons (units that replicate).
Plasmid copy numbers are tightly controlled within a cell by plasmid-encoded genes, maintaining a suitable number.
Bacteriophage DNA might exist within the bacterial cell.

Plasmids

Plasmids are smaller than bacterial chromosomes.
They typically do not encode essential housekeeping genes (e.g., DNA/RNA polymerases, ribosomes).
Antibiotic resistance genes are frequently found on plasmids.
Plasmid replication is regulated by plasmid-encoded genes. Plasmids with similar replication controls are incompatible (Inc) – only one such plasmid will be maintained at target copy number.

Mutations and Genetic Terminology

Wild-type strain: The typical, naturally occurring strain that serves as a baseline for comparison.
Mutant strain: A strain with a mutation that changes its traits relative to the wild-type.
Mutation: A change in the gene sequence that alters its function.
Allele: Different versions of a gene.
Auxotroph: A mutant unable to synthesize a specific compound, leading to a nutritional requirement.
Prototroph: A strain capable of producing all essential organic compounds.
Genotype: The genetic makeup (sequence) of an organism, often compared to the wild type.
Phenotype: The observable characteristics of an organism resulting from its genotype.

Studying Bacterial Mutants

Bacteria are excellent for genetic research due to their single chromosome, enabling easier mutation detection.
Early studies focused on nutritional mutants to understand gene function by studying growth requirements.
Phenotypic changes can reveal mutations in exopolysaccharides, carbon utilization, or nutritional requirements.

Methods of Identifying Mutants

Selection: Identifying mutants based on growth under specific conditions (e.g., antibiotic resistance). Mutants that survive selective pressure are isolated and studied.
Screening: The visual or experimental identification of mutants based on observable traits (e.g., color, morphology, or lack of growth in certain media).
Replica Plating: A screening technique using velvet or patching to transfer colonies from one plate to another to identify mutants based on their different growth patterns on selective or incomplete media.

Types of Mutations and Reversion

Silent mutation: No change in the protein's amino acid sequence.
Missense mutation: Change in a codon, leading to a different amino acid.
Nonsense mutation: Early stop codon creation.
Frameshift mutation: Deletion or insertion of nucleotides, altering the entire downstream amino acid sequence.
Reversion: A mutation correcting a metabolic defect to the wild-type state.

Spontaneous Mutations and Evolution

Spontaneous mutations can occur without external influences.
Experiments by Esther Lederberg and Luria and Delbruck demonstrated the spontaneous development of mutations, even under non-selective conditions.
Lenski's E. coli long-term evolution experiments showed adaptation and evolutionary changes over multiple generations.

Restriction Enzymes and Cloning

Restriction enzymes (REs) are bacterial defense mechanisms that cut DNA at specific recognition sites, often palindromic sequences.
Modification enzymes (methyltransferases) protect a cell's own DNA from being cut by the same restriction enzymes.
Restriction enzymes and cloning vectors allow researchers to cut and paste DNA fragments together, creating recombinant DNA molecules.

Cloning Vectors

Plasmids, bacteriophages, and cosmids are cloning vectors.
Plasmids, especially the pBR322 vector, are widely used due to their features: origin of replication, antibiotic resistance genes (selectable markers), multiple cloning site, and small size.

Cloning Methods

Cloning involves inserting a gene of interest into a cloning vector.
Screening is done to identify bacterial clones carrying the recombinant plasmid.

DNA Transfer and Transformation

Transformation involves transferring extracellular DNA directly into a recipient cell.
Natural competence and artificial induction methods (calcium chloride treatment, electroporation) are used.

Other Genetic Transfer Mechanisms (Conjugation, Transduction, Transposition)

Conjugation: Direct transfer of DNA between bacterial cells via cell-to-cell contact. Involves the transfer of the F plasmid which can sometimes integrate into the chromosome leading to high frequency recombination strains (Hfr).
Transduction: Transfer of genetic material via viruses. This can be generalized (lytic cycle) or specialized (lysogenic cycle).
Transposition: Movement of DNA segments within or between genomes using transposable elements.

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Description

Test your knowledge on E. Coli K12 and the pioneers of microbial genetics. This quiz covers important aspects such as plasmid-encoded genes and the understanding of bacterial gene functions. Challenge yourself and discover how much you know about bacterial genetics!