BIO-31 Ch.8 part 2
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Questions and Answers

What is the typical size range of plasmids compared to a bacterial chromosome?

  • 10 to 20% the size
  • 1 to 5% the size (correct)
  • 25 to 40% the size
  • 50 to 75% the size

What process involves a bacteriophage transferring genetic material from one bacterium to another?

  • Transformation
  • Conjugation
  • Transduction (correct)
  • Translation

What is the role of mutations and recombination in the context of evolution?

  • They ensure survival of all organisms.
  • They create cell diversity. (correct)
  • They prevent natural selection.
  • They limit cell diversity.

What kind of genes do R factors encode?

<p>Antibiotic resistance (D)</p> Signup and view all the answers

What acts on populations of organisms to ensure the survival of organisms fit for a particular environment?

<p>Natural selection (D)</p> Signup and view all the answers

What type of genes are expressed at a fixed rate?

<p>Constitutive genes (A)</p> Signup and view all the answers

What is the function of a repressor in gene expression?

<p>To block transcription (A)</p> Signup and view all the answers

What is the default position of a repressible gene?

<p>On (C)</p> Signup and view all the answers

What segment of DNA does RNA polymerase initially bind to?

<p>Promoter (A)</p> Signup and view all the answers

What is the function of the operator in the operon model?

<p>To control transcription (D)</p> Signup and view all the answers

What comprises an operon?

<p>Promoter and operator sites and the structural genes they control (A)</p> Signup and view all the answers

In an inducible operon, what must be present for structural genes to be transcribed?

<p>An inducer (A)</p> Signup and view all the answers

In the lac operon, what happens in the absence of lactose?

<p>The repressor binds to the operator, preventing transcription (A)</p> Signup and view all the answers

In a repressible operon, structural genes are transcribed until what occurs?

<p>They are turned off (C)</p> Signup and view all the answers

What is the role of excess tryptophan in a repressible operon?

<p>It acts as a corepressor, activating the repressor (B)</p> Signup and view all the answers

What is a mutation?

<p>A permanent change in the DNA base sequence (C)</p> Signup and view all the answers

Mutations can be all of the following EXCEPT:

<p>Reversible (D)</p> Signup and view all the answers

What are agents that cause mutations called?

<p>Mutagens (D)</p> Signup and view all the answers

What is a base substitution mutation also known as?

<p>Point mutation (B)</p> Signup and view all the answers

What is the result of a missense mutation?

<p>Change in one amino acid (B)</p> Signup and view all the answers

What does a nonsense mutation result in?

<p>A premature stop codon (C)</p> Signup and view all the answers

What type of mutation involves the insertion or deletion of nucleotide pairs?

<p>Frameshift mutation (A)</p> Signup and view all the answers

What does nitrous acid cause adenine to bind with instead of thymine?

<p>Cytosine (C)</p> Signup and view all the answers

Which type of radiation causes the formation of thymine dimers?

<p>UV radiation (D)</p> Signup and view all the answers

What is the function of photolyases?

<p>To separate thymine dimers (D)</p> Signup and view all the answers

What is the typical spontaneous mutation rate in replicated genes?

<p>1 in 1,000,000 (D)</p> Signup and view all the answers

What do mutagens typically do to the spontaneous mutation rate?

<p>Increase it (C)</p> Signup and view all the answers

What does positive (direct) selection detect?

<p>Mutant cells that grow differently (B)</p> Signup and view all the answers

What are mutant cells with a nutritional requirement absent in the parent strain called?

<p>Auxotrophs (B)</p> Signup and view all the answers

What is the purpose of the Ames test?

<p>To measure the rate of mutation reversal (D)</p> Signup and view all the answers

Methylase is an enzyme that adds a methyl group to which base in the sequence 5'-GATC-3'?

<p>Adenine (D)</p> Signup and view all the answers

What is the initial step in nucleotide excision repair?

<p>Cutting out incorrect bases (B)</p> Signup and view all the answers

What characteristic of a new DNA strand is important for nucleotide excision repair?

<p>Being nonmethylated (C)</p> Signup and view all the answers

What is genetic recombination?

<p>The exchange of genes between two DNA molecules (C)</p> Signup and view all the answers

What is the result of crossing over?

<p>The insertion of foreign DNA into a chromosome (B)</p> Signup and view all the answers

What is vertical gene transfer?

<p>Transfer of genes from an organism to its offspring (D)</p> Signup and view all the answers

Which of the following is NOT a mechanism of horizontal gene transfer?

<p>Replication (A)</p> Signup and view all the answers

What is transformation in bacteria?

<p>Uptake of 'naked' DNA from the environment (D)</p> Signup and view all the answers

What structure is required for conjugation in bacteria?

<p>Sex pili (B)</p> Signup and view all the answers

What is the role of the F factor in bacterial conjugation?

<p>It carries the plasmid to be transferred. (C)</p> Signup and view all the answers

What are R plasmids (R factors)?

<p>Plasmids that contain genes for antibiotic resistance (C)</p> Signup and view all the answers

What is a bacteriophage?

<p>A virus that infects bacteria (C)</p> Signup and view all the answers

What mediates transduction in bacteria?

<p>Bacteriophages (D)</p> Signup and view all the answers

Flashcards

Constitutive Genes

Genes expressed at a constant rate.

Regulated Genes

Genes expressed only when needed.

Repression

Inhibits gene expression; decreases enzyme synthesis.

Induction

Turns on gene expression.

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Promoter

Segment of DNA where RNA polymerase initiates transcription.

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Operator

Segment of DNA that controls transcription (stop/go).

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Operon

Set of operator and promoter sites, and structural genes they control.

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Inducible Operon

Structural genes are not transcribed unless an inducer is present.

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Repressible Operon

A model of gene expression where structural genes are transcribed until turned off.

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Tryptophan in Repressible Operons

Excess of this amino acid acts as a corepressor, activating the repressor to halt its own synthesis.

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Mutation

A permanent alteration in the DNA base sequence.

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Mutagens

Agents that induce mutations.

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Spontaneous Mutations

Mutations occurring without the presence of a mutagen.

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Base Substitution (Point Mutation)

Mutation where one base in the DNA is changed.

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Missense Mutation

Base substitution resulting in an amino acid change.

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Nonsense Mutation

Base substitution resulting in a stop codon.

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Frameshift Mutation

Insertion or deletion of nucleotides, shifting the reading frame.

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Nitrous Acid (as a mutagen)

Chemical that causes adenine to bind with cytosine instead of thymine.

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Transduction

Transfer of DNA between bacteria via bacteriophages (viruses that infect bacteria).

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Plasmids

Small, circular, self-replicating DNA molecules in bacteria, separate from the chromosome.

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Resistance Factors (R factors)

Plasmids that carry genes for antibiotic resistance.

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Cell Diversity

The raw material for evolution, arising from mutations and recombination.

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Natural Selection

Acts on populations with diversity to favor survival of the fittest.

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Radiation Mutagen

A substance that causes mutations.

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Ionizing Radiation Effects

Ionizing radiation that forms ions, oxidizes nucleotides, and breaks deoxyribose-phosphate backbone.

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UV Radiation Effects

Non-ionizing radiation that causes thymine dimers (intra-strand bonding).

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Photolyases Function

Enzymes use visible light energy to separate thymine dimers.

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Nucleotide Excision Repair

Enzymes cut out incorrect bases and fill in correct bases, repairing all mutations on nonmethylated strand.

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Methylase Function

An enzyme that adds a methyl group to the adenine of the sequence 5'-GATC-3' in newly synthesized DNA.

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Spontaneous Mutation Rate

Spontaneous mutations happen in 1 in 1,000,000 replicated genes (10-6).

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Positive (Direct) Selection

Detects mutant cells because they grow or appear different than unmutated cells.

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Negative (Indirect) Selection

Detects mutant cells that cannot grow or perform a certain function.

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Auxotroph Definition

Mutant that has a nutritional requirement absent in the parent.

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Genetic recombination

Exchange of genes between two DNA molecules, creating genetic diversity.

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Crossing over

Two chromosomes break and rejoin, inserting foreign DNA.

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Vertical gene transfer

Transfer of genes from parent to offspring.

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Horizontal (lateral) gene transfer

Gene transfer between cells of the same generation.

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Transformation (in bacteria)

Genes transferred as 'naked' DNA from one bacterium to another.

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Conjugation (in bacteria)

Plasmids transferred from one bacterium to another via cell-to-cell contact.

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F+ cells (donor cells)

Cells carrying a plasmid (F factor).

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R plasmids (R factors)

A plasmid that can be transferred during conjugation.

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Transduction (in bacteria)

DNA transferred from a donor to a recipient via a virus.

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Generalized transduction

Random bacterial DNA is packaged inside a phage and transferred.

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