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Questions and Answers
What is the term for phage DNA that becomes part of the host cell's genome?
What is the term for phage DNA that becomes part of the host cell's genome?
Which bacterial defense system involves cutting DNA at specific nucleotide sequences?
Which bacterial defense system involves cutting DNA at specific nucleotide sequences?
Who were awarded the 2020 Nobel Prize for their work on CRISPR systems?
Who were awarded the 2020 Nobel Prize for their work on CRISPR systems?
What enzyme protects a cell's own DNA from being cut by adding methyl groups?
What enzyme protects a cell's own DNA from being cut by adding methyl groups?
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What complex cuts invading DNA into short fragments in CRISPR systems?
What complex cuts invading DNA into short fragments in CRISPR systems?
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Why are bacterial defenses against invading DNA important in biotechnology?
Why are bacterial defenses against invading DNA important in biotechnology?
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What happens when a cut is made using restriction enzymes in biotechnology?
What happens when a cut is made using restriction enzymes in biotechnology?
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'CRISPR' stands for:
'CRISPR' stands for:
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Study Notes
Genetic Change in Bacteria
- Two mechanisms of genetic change in bacteria: mutation and horizontal gene transfer
- Changes are passed to progeny by vertical gene transfer
Mutation
- A change in an organism's DNA that alters its genotype
- Can occur spontaneously or be induced by mutagens
- Can result in a change in the phenotype of the organism
Types of Mutations
- Point mutations: a change in a single nucleotide
- Frameshift mutations: the insertion or deletion of one or more nucleotides, leading to a change in the reading frame of the genetic code
- Deletions: the removal of one or more nucleotides
- Insertions: the addition of one or more nucleotides
Effects of Mutations
- May result in a change in the function of a protein
- Can affect the growth and survival of an organism
- Can influence an organism's response to environmental factors
Induced Mutations
- Caused by external factors such as radiation and chemicals
- Can be used intentionally to generate mutations in bacteria
Repair of Damaged DNA
- Enzymes can repair damaged DNA by fixing errors in nucleotide incorporation
- Two mechanisms of repair: proofreading by DNA polymerase and mismatch repair
- SOS repair is a last-ditch repair mechanism used when other systems fail
Screening for Possible Carcinogens
- The Ames test measures the effect of a chemical on the reversion rate of a histidine-requiring Salmonella auxotroph
- Mutagens increase the frequency of spontaneous reversions
Plasmid Transfer
- Plasmids are small, self-replicating circular DNA molecules
- Can be transferred from one bacterium to another through conjugation
- F plasmid is involved in conjugation and is integrated into the chromosome of the donor cell
Chromosome Transfer
- Involves the transfer of part of the chromosome from one bacterium to another
- F′ plasmid is formed when a small piece of the chromosome is removed with the F plasmid
Genome Variability
- Much variation in the genes of different strains of a single species
- Less than 50% of the genes are shared between different strains of E. coli
Transposons
- Pieces of DNA that can move from one location to another in a cell's genome
- Can move into other replicons in the same cell
- Can integrate into the chromosome via non-homologous recombination
Genomic Islands
- Large DNA segments in a genome that originated in other species
- Nucleotide composition is very different from the rest of the genome
- Characteristics encoded by genomic islands include the use of specific energy sources and acid tolerance
Phage DNA
- Certain types of bacteriophages can insert their DNA into the host cell chromosome
- Phage DNA becomes part of the host cell's genome and is replicated and passed on to progeny cells
Bacterial Defenses Against Invading DNA
- Restriction-modification systems recognize and destroy foreign DNA that enters the cell
- CRISPR systems include small segments of phage DNA that recognize specific DNA and direct DNA-cutting enzymes to invading DNA
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Description
Learn about the mechanisms of plasmid and chromosome transfer in bacteria, focusing on F pilus binding, contraction, and DNA strand transfer. Explore how bacterial cells become F+ through plasmid transfer and understand the process of complementary strand synthesis.
