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What does the term 'genotype' refer to?
Bacteria have a dominant and recessive state for chromosomes.
False
What is a codon?
A set of 3 nucleotide bases coding for an amino acid.
The totality of genetic information in an organism is referred to as the ______.
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Match the following terms with their definitions:
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What is transferred during conjugation?
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Only F+ cells can act as donors in conjugation.
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What forms the temporary cytoplasmic bridge during conjugation?
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The F plasmid can integrate with the bacterial chromosome to form an ________ cell.
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Match the following terms related to conjugation with their definitions:
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What is the length of E. coli DNA?
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RNA has a different structure than DNA in that it is double stranded.
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What is the process by which bacteria reproduce?
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The process of DNA replication involves ________, which unzips the parental DNA strand.
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Match the following components of DNA replication with their functions:
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Which of the following describes plasmids?
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R-plasmids carry genes that help bacteria resist certain antibiotics.
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What are the short DNA fragments formed during lagging strand synthesis called?
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What is the main consequence of frameshift mutations?
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Base analogs can pair incorrectly during DNA replication.
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What is one common physical agent that causes mutations in bacteria?
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In frameshift mutations, an insertion or deletion of a nucleotide alters the ________ grouping of nucleotides.
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Match the following types of mutagens with their descriptions:
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Which error is commonly corrected by DNA proof reading during replication?
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The incorporation of a base analog into DNA always results in a frameshift mutation.
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What type of mutation results from the deletion of a nucleotide?
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What is the process called when a bacterium takes up naked DNA from the environment?
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Transduction involves the direct transfer of DNA between two bacteria without the help of a virus.
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What type of cell is produced after successful recombination during transformation?
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The _______ cycle of a bacteriophage results in cell death.
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Match the following bacteriophages with their replication type:
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Which statement best describes the fate of DNA that is taken up by a bacterium but not integrated into its DNA?
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A recombinant cell will have a genetic makeup that is identical to either the donor or the recipient cell.
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What does the term 'generalized transduction' refer to?
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Study Notes
Bacterial Genetics
- Genetics is the study of heredity.
- Heredity is the transfer of traits from an organism to its offspring.
- Phenotype is the observable traits of an organism.
- Genotype is the genetic makeup of an organism that determines its phenotype.
- Genome encompasses all the genetic information in an organism, including chromosomal DNA and plasmids.
- Chromosome is coiled and supercoiled DNA that is haploid in bacteria. It does not have recessive or dominant states.
- Gene is a unit of inheritance, a segment of DNA that performs a specific function, such as coding for an amino acid or a polypeptide.
- Codon is a set of three nucleotide bases that code for an amino acid.
DNA Structure
- DNA is double-stranded, forming a double helix with two anti-parallel chains (5' to 3' and 3' to 5').
- The strands are held together by complementary base pairing: Adenine (A) pairs with Thymine (T) and Guanine (G) with Cytosine (C).
- Bacterial DNA is closed and circular.
- DNA is coiled and supercoiled to form a chromosome, allowing it to fit within the bacterial cell.
RNA Structure
- RNA is similar to DNA but differs in the following ways:
- It is single-stranded.
- Uracil (U) replaces Thymine (T).
DNA Replication
- Bacteria reproduce through binary fission, which involves copying the chromosome and dividing the cell.
- DNA replication starts with the uncoiling of the chromosome back into DNA by DNA helicase and gyrase.
- The unzipped DNA forms a replication fork.
- The leading strand is synthesized continuously (5' to 3').
- DNA polymerase adds complimentary nucleotides to the template strand, building the growing strand.
- The lagging strand is synthesized discontinuously (3' to 5').
- RNA polymerase creates a short RNA primer.
- DNA polymerase extends the RNA primer, adding complimentary nucleotides.
- DNA polymerase removes the RNA primer and replaces it with DNA, forming short DNA fragments called Okazaki fragments.
- DNA ligase joins the Okazaki fragments together.
Plasmids
- Plasmids are small, circular pieces of DNA that replicate independently of the bacterial chromosome.
- They are important for:
- Mutation: F-plasmid
- Resistance: R-plasmid
- R-plasmids carry genes that confer antibiotic resistance.
Mutations
- Frameshift mutations are caused by base insertion or deletion, altering the codon sequence and resulting in a protein with extensive missense (incorrect amino acid) or premature termination (nonsense) due to a stop codon.
Causes of Mutation in Bacteria
- Errors during replication, repair, or recombination: Proofreading mechanisms exist, but errors can still occur.
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Exposure to chemical mutagens:
- Nitrous Acid modifies base pairing (adenine pairs with cytosine instead of thymine).
- Base analogs are similar to DNA bases but have different pairing properties, leading to base-pair substitutions.
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Exposure to physical mutagens:
- UV light induces thymine dimer formation, disrupting DNA replication and transcription.
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Genetic transfer in bacteria:
- Transfer of DNA fragments from donor to recipient cells, leading to recombination and possible mutations.
Mechanisms of Genetic Transfer in Bacteria
- Transformation: A bacterium takes up naked DNA fragments from the environment (e.g., from lysed cells).
- Transduction: DNA is transferred from one bacterium to another via a bacteriophage (phage) that infects bacteria.
- Conjugation: Genetic material is transferred between bacterial cells through a conjugation bridge formed by a sex pilus.
Transformation
- The uptake of DNA from the environment can lead to the integration of the new DNA into the recipient's chromosome through recombination.
- The resulting cell is called a transformed cell, which is a mutant cell with a different genetic makeup compared to the donor and recipient.
- All descendants of the transformed cell will be identical to the parent cell.
Transduction
- Transduction involves a bacteriophage (phage), a virus that infects bacteria.
- Two types of transduction exist:
- Generalized transduction: Lytic cycle is used, any part of bacterial DNA can be transferred.
- Specialized transduction: Lysogenic cycle is used, a specific part of bacterial DNA is transferred.
Conjugation
- Genetic material is transferred between bacterial cells through a conjugation bridge.
- The donor cell is called F+ or male, possessing the F plasmid.
- The recipient cell is called F- or female.
- The F plasmid can integrate into the bacterial chromosome, forming an Hfr (high frequency of recombination) cell.
- Hfr cells can transfer the F plasmid and some bacterial chromosomal DNA to F- cells.
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Description
This quiz covers fundamental concepts of bacterial genetics, including heredity, genotype, phenotype, and the structure of DNA. Explore how genetic information is transferred and expressed in bacteria. Test your knowledge of key genetic terms and their significance.
