BIOL 261: CH. 9 - GENETICS OF BACTERIA AND ARCHAEA

What is a mutation?

A mutation is a heritable change in the genome.

What is the genotype of an organism?

The genotype is the sequence of nucleotides in a gene.

How can mutations affect an organism?

Mutations can lead to changes in the properties of an organism; some are beneficial, some are detrimental, and most have no effect.

Why do prokaryotes accumulate mutations quickly?

Prokaryotes accumulate mutations quickly due to their exponential growth.

What is horizontal gene transfer?

Horizontal gene transfer is the movement of genes between cells other than through reproduction.

How does horizontal gene transfer impact genetic changes?

Horizontal gene transfer generates much larger genetic changes compared to mutations alone.

What fuels evolution in bacteria and archaea?

Mutation and genetic exchange fuel evolution in bacteria and archaea.

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What is transfection?

Transfection is the uptake of free viral DNA.

What is conjugation?

Conjugation is the transfer of either the F plasmid or part of the chromosome between two bacteria.

What is a selectable mutation?

A selectable mutation is a mutation that confers an advantage under certain environmental conditions, allowing progeny cells to outgrow and replace the parent cells.

What is an example of a selectable mutation?

An example of a selectable mutation is antibiotic resistance, where bacteria with the mutation can survive and grow in the presence of an antibiotic.

How can selectable mutations be detected?

Selectable mutations can be detected by growing organisms under specific conditions that favor the mutated cells, making it easier to identify them.

Why are selectable mutations advantageous for studying genetics?

Selectable mutations are advantageous for studying genetics because they allow researchers to easily identify and isolate mutant cells that survive under specific conditions.

How can antibiotic resistance be used to select for mutants?

Antibiotic resistance can be used to select for mutants by growing bacteria on media containing the antibiotic, where only resistant bacteria will grow.

What is an example of a method used to isolate antibiotic-resistant bacteria?

A method used to isolate antibiotic-resistant bacteria is growing them on L-agar with Ampicillin, where only Ampicillin-resistant bacteria will survive.

Why is it relatively easy to detect selectable mutations?

Selectable mutations are relatively easy to detect because they provide an advantage, allowing mutant cells to outgrow and replace non-mutant cells.

What is a nonselectable mutation?

A nonselectable mutation is a mutation that does not provide an advantage but may still result in a phenotypic change.

What is an example of a nonselectable mutation?

An example of a nonselectable mutation is the loss of pigmentation in an organism, which does not provide a survival advantage but results in a visible change.

How can nonselectable mutations be identified?

Nonselectable mutations can be identified through screening, which involves examining large numbers of organisms and looking for phenotypic differences.

Why is screening for nonselectable mutations laborious and time-consuming?

Screening for nonselectable mutations is laborious and time-consuming because it requires analyzing many organisms individually to detect changes that do not confer a survival advantage.

What is the difference between screening and selection in mutant isolation?

Screening involves examining large numbers of organisms for phenotypic differences without an advantage, while selection allows mutants to outcompete non-mutants under specific conditions.

Why is selection a more efficient method for isolating mutants than screening?

Selection is more efficient because it allows researchers to grow only the mutants of interest, whereas screening requires analyzing many individuals to find differences.

Why are selectable mutations considered a powerful genetic tool?

Selectable mutations are a powerful genetic tool because they enable researchers to easily isolate and study mutants based on their ability to survive under specific conditions.

What is an auxotrophic mutant?

An auxotrophic mutant has a nutritional requirement for growth.

What is an example of an auxotrophic mutant?

An example of an auxotrophic mutant is one that requires histidine (an amino acid) in the media to grow.

What method is used to screen for auxotrophic mutants?

Auxotrophic mutants are screened using a method called replica plating.

What are the two main types of mutations?

The two main types of mutations are spontaneous mutations and induced mutations.

How do spontaneous mutations occur?

Spontaneous mutations occur without external intervention, usually due to occasional errors by DNA polymerase during replication.

What causes induced mutations?

Induced mutations are caused by environmental or deliberate factors, such as radiation or chemicals that modify DNA.

What are some examples of environmental factors that can cause induced mutations?

Examples include UV light, chemicals, and pesticides.

What is a point mutation?

A point mutation is a mutation that changes only one base pair in the DNA sequence.

What are the three types of point mutations?

The three types of point mutations are substitution, addition, and subtraction.

What happens during a substitution mutation?

During a substitution mutation, one base is replaced by another.

What happens during an addition mutation?

During an addition mutation, an extra base is added to the DNA sequence.

What happens during a subtraction mutation?

During a subtraction mutation, a base is removed from the DNA sequence.

How does a point mutation affect the flow of genetic information?

A point mutation affects DNA, which is transcribed into mRNA, translated into codons, and then used to assemble amino acids into proteins.

What is a silent mutation?

A silent mutation is a mutation that does not change the amino acid sequence of the resulting protein.

How can a point mutation lead to a change in the amino acid sequence?

A point mutation can change the codon sequence, resulting in a different amino acid and producing a different protein.

What is a missense mutation?

A missense mutation is a type of point mutation that changes the amino acid sequence, leading to a different protein.

What is a nonsense mutation?

A nonsense mutation is a type of point mutation that results in a stop codon, leading to a faulty or incomplete protein.

How can a nonsense mutation affect the cell?

A nonsense mutation can create a faulty protein, which may be fatal and result in the death of the cell.

What determines the phenotypic change caused by a point mutation?

The phenotypic change depends on the exact location of the mutation within the gene.

What do mutation rates depend on?

Mutation rates depend on the frequency of DNA changes and the efficiency of DNA repair.

What are reversions and suppressors?

Reversions, also known as back mutations, and suppressors are mechanisms that can restore function or phenotype after a mutation.

Why do reversions occur?

Reversions occur because point mutations are typically reversible.

What happens in a reversion?

In a reversion, the DNA sequence changes back to its normal state.

What are nucleotide base analogs?

Nucleotide base analogs resemble nucleotide bases but have faulty base pairing.

How do nucleotide base analogs affect DNA replication?

Nucleotide base analogs cause replication errors to occur at higher frequencies due to incorrect base pairing.

What is an example of a nucleotide base analog?

An example of a nucleotide base analog is AZT.

What is the consequence of incorrect base pairing caused by nucleotide base analogs?

Incorrect base pairing caused by nucleotide base analogs results in mismatched base incorporation, leading to mutation.

What is ethidium bromide used for?

Ethidium bromide is a stain used to stain DNA gels.

What type of agent is ethidium bromide?

Ethidium bromide is an intercalating agent that gets between DNA bases.

What is a major health risk associated with ethidium bromide?

Ethidium bromide is a carcinogen.

What effect do gamma rays have on DNA?

Gamma rays cause breaks in the DNA.

Why are shorter gamma ray wavelengths more dangerous?

Shorter gamma ray wavelengths penetrate more, making them more deadly.

What type of DNA damage is caused by UV light?

UV light causes T-T dimers.

How does the SOS repair mechanism respond to UV-induced DNA damage?

The SOS repair mechanism cuts out the mutation and replaces the base to "fix" the DNA.

What is transformation in bacteria?

Transformation is the uptake of free DNA by competent cells.

What are competent cells?

Competent cells are cells that are capable of taking up DNA from their environment.

Who conducted the first transformation experiment?

Griffith conducted the first transformation experiment.

What happened in Griffith's experiment when dead smooth cells were mixed with live R cells?

The dead smooth cells were mixed with live R cells, and the R cells were lysed.

What was the result of Griffith's experiment when mice were injected with the mixture of dead smooth cells and live R cells?

The mice died because the live R cells picked up the gene for the capsule and became smooth cells, which caused pneumonia.

Why did bacteria grow in Griffith's experiment after the transformation?

Bacteria grew because they went through transformation, acquiring the gene for the capsule.

Is Streptococcus pneumoniae naturally competent?

Yes, Streptococcus pneumoniae is naturally competent.

Is Escherichia coli naturally competent?

No, Escherichia coli is not naturally competent.

Can Escherichia coli be made competent?

Yes, Escherichia coli can be made competent using cold calcium chloride (Ca²⁺).

What is the definition of transduction?

Transduction is the transfer of DNA from one cell to another by a bacteriophage.

What are the two modes of transduction?

The two modes of transduction are generalized transduction and specialized transduction.

What happens during generalized transduction?

During generalized transduction, DNA from any portion of the host genome is packaged inside the virion.

What type of phage is involved in generalized transduction?

Lytic phages, such as T₄, are involved in generalized transduction.

Can donor genes replicate independently in generalized transduction?

No, donor genes cannot replicate independently in generalized transduction.

What happens to donor genes without recombination in generalized transduction?

Without recombination, donor genes will be lost in generalized transduction.

What happens during specialized transduction?

During specialized transduction, DNA from a specific region of the host chromosome is integrated directly into the virus genome, typically replacing some viral genes.

What type of phage is involved in specialized transduction?

Lysogenic phages, such as lambda, are involved in specialized transduction.

How does the viral DNA behave in specialized transduction?

In specialized transduction, the viral DNA incorporates into the host chromosome.

What is a transducing phage?

A transducing phage is a bacterial virus carrying bacterial genes.

What may occur during specialized transduction involving bacterial DNA?

Homologous recombination may occur during specialized transduction, or the bacterial DNA may be integrated during lysogeny.

Where does transduction occur?

Transduction occurs in many bacteria and at least one archaea.

What are some examples of transduction in bacteria?

Examples of transduction in bacteria include the transfer of multiple-antibiotic-resistance genes in Salmonella, Shiga-like toxins in Escherichia coli, virulence factors in Vibrio cholerae, and photosynthetic genes in cyanobacteria.

What is conjugation in the context of horizontal gene transfer?

Conjugation is a process of horizontal gene transfer that requires cell-to-cell contact, involving the transfer of the F plasmid from one cell to another via a pilus.

How does conjugation occur between cells?

Conjugation occurs when the F+ donor cell transfers the entire plasmid to the recipient F- cell, potentially mobilizing other genetic elements such as additional plasmids or the host chromosome.

What is the role of the F+ and F- cells in conjugation?

The F+ cell is the donor that contains the conjugative plasmid, while the F- cell is the recipient that does not contain the plasmid.

Can conjugation occur between closely related or distantly related cells?

Yes, conjugation can occur between both closely related and distantly related cells.

What are the plasmid-encoded factors in conjugation?

The plasmid-encoded factors are responsible for the transfer of the plasmid during conjugation.

What is rolling circle replication of the F plasmid?

Rolling circle replication of the F plasmid is a process where a single-stranded DNA copy of the plasmid is transferred from one bacterial cell to another during conjugation.

• The F plasmid undergoes replication in a way that creates a rolling structure, allowing the transfer of genetic material.

What are cells possessing an integrated F plasmid known as?

Cells possessing an integrated F plasmid are known as Hfr cells.

What does high frequency of recombination (Hfr) lead to between genes on the donor and recipient chromosomes?

High frequency of recombination leads to high rates of genetic recombination between genes on the donor (Hfr) and recipient (F−) chromosomes.

How does integration of the F plasmid provide a mechanism for mobilizing a genome?

Integration of the F plasmid provides a mechanism for mobilizing a genome by allowing the transfer of genetic material between the donor and recipient cells.

What are insertion sequences and transposons?

Insertion sequences and transposons are pieces of DNA that move in and out of chromosomes.

What is CRISPR?

CRISPR is a system found within bacteria that acts as an immune mechanism, allowing the bacteria to recognize and fight off viral infections.

What do restriction enzymes do?

Restriction enzymes cut up DNA and RNA.

Where do restriction enzymes cut?

Restriction enzymes cut at restriction sites.

Distinguish between a mutation and a mutant.

A mutation is a change in the DNA sequence, while a mutant is an organism or cell that carries a mutation.

Distinguish between screening and selection.

Screening involves looking for a specific characteristic in a population, whereas selection involves choosing organisms with desired traits based on their survival or growth.

What is an auxotrophic mutant?  How would you screen for it?

An auxotrophic mutant is a mutant that cannot synthesize a particular compound required for its growth.

• You would screen for it by growing the organism on a medium lacking that compound and observing if it survives.

Why do frameshift mutations generally have more serious consequences than missense mutations?

Frameshift mutations generally have more serious consequences because they alter the entire reading frame of the gene, leading to a completely different and usually nonfunctional protein, while missense mutations only change one amino acid.

How is a missense, nonsense, and silent mutation similar and different?

All three are types of point mutations, but missense mutations change one amino acid, nonsense mutations create a premature stop codon, and silent mutations do not change the protein sequence.

How do mutagens cause mutations?  What are some examples of mutagens?

Mutagens cause mutations by inducing changes in the DNA sequence.

• Examples of mutagens include radiation, chemicals, and certain viruses.