Question 1

A researcher performs a serial dilution of a bacterial culture and plates 0.1 mL of a $$10^{-5}$$ dilution on an agar plate. After incubation, 75 colonies are counted. What is the original concentration of bacteria in the culture (in bacteria/mL)?

Accepted Answer

$$7.5 	imes 10$$^{6}$$

Question 2

Which of the following best describes the difference between conjugation and transduction in bacteria?

Accepted Answer

Conjugation requires direct cell-to-cell contact, while transduction involves bacteriophages transferring DNA between cells.

Question 3

During an Hfr × F− mating, which of the following outcomes is most likely?

Accepted Answer

The F− cell may acquire new chromosomal genes but usually remains F−.

Question 4

Which enzyme is responsible for charging tRNA molecules with their corresponding amino acids, and what is the source of energy for this process?

Accepted Answer

Aminoacyl-tRNA synthetase; ATP

Question 5

A mutation changes a codon from UAU (tyrosine) to UGU (cysteine). What type of mutation is this?

Accepted Answer

Transversion

Question 6

Which of the following best explains why peptide bonds are considered 'special' in proteins?

Accepted Answer

They have partial double-bond character, restricting rotation and stabilizing protein structure.

Question 7

In the classic experiment by Beadle and Tatum, which hypothesis was supported by their work with Neurospora crassa?

Accepted Answer

One gene: one enzyme hypothesis

Question 8

Which of the following is a key difference between translation in prokaryotes and eukaryotes?

Accepted Answer

In eukaryotes, translation occurs in the cytoplasm after mRNA processing, while in prokaryotes, it can begin before transcription is complete.

Question 9

A patient is exposed to UV light, resulting in the formation of thymine dimers in their DNA. Which DNA repair mechanism is most directly involved in repairing this damage, and what enzyme is required?

Accepted Answer

Photoreactivation repair; photolyase

Question 10

Which of the following best describes a repressible operon?

Accepted Answer

It is usually on but can be turned off when a corepressor is present.

Question 11

In the lac operon, what is the effect of a mutation in the operator region (O^c) that prevents the repressor from binding?

Accepted Answer

The operon is constitutively expressed, regardless of lactose presence.

Question 12

Which of the following is NOT a typical component of a bacterial operon?

Accepted Answer

Enhancer

Question 13

A scientist wants to amplify a specific DNA sequence from a small sample. Which technique should they use, and what is the basic principle behind it?

Accepted Answer

Polymerase Chain Reaction (PCR); repeated cycles of denaturation, annealing, and extension

Question 14

Which type of vector would be most appropriate for cloning a 200 kb fragment of human DNA?

Accepted Answer

Bacterial Artificial Chromosome (BAC)

Question 15

A frameshift mutation is most likely to result from which of the following?

Accepted Answer

Insertion or deletion of a single nucleotide

Question 16

Which of the following best describes the process of attenuation in the trp operon?

Accepted Answer

Premature termination of transcription in response to high tryptophan levels

Question 17

Which of the following is a key step in constructing a cDNA library?

Accepted Answer

Reverse transcription of mRNA to synthesize complementary DNA

Question 18

A knockout mouse is created by which of the following processes?

Accepted Answer

Targeted disruption of a specific gene in embryonic stem cells, followed by incorporation into a developing embryo

Question 19

Which of the following best describes the principle of Sanger DNA sequencing?

Accepted Answer

Incorporation of chain-terminating dideoxynucleotides during DNA synthesis

Question 20

A patient is diagnosed with sickle cell anemia, which is caused by a single nucleotide substitution in the beta-globin gene. What type of mutation is this, and what is the most likely effect on the protein?

Accepted Answer

Missense mutation; changes one amino acid in the protein

Genetics Exam III Study Guide: Bacterial Genetics, Translation, Mutation & Repair, Gene Regulation, and Recombinant DNA Technology

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