Q: In DNA, which type of bond connects the 3' carbon of one deoxyribose to the 5' phosphate of the next nucleotide?

Phosphodiester bond: $$\mathrm{3'\text{-}OH\ +\ 5'\text{-}PO_4$^{2-}\ \rightarrow\ phosphodiester\ bond}$$

Question 1

Which of the following features makes bacteria particularly advantageous for genetic studies compared to eukaryotes?

Accepted Answer

Bacteria have a single, circular chromosome and reproduce rapidly by binary fission, allowing for quick observation of genetic changes.

Question 2

A bacterial strain can grow on minimal medium but not when tryptophan is omitted. What is the genotype of this strain with respect to tryptophan biosynthesis?

Accepted Answer

trp-

Question 3

After conjugation between an Hfr cell and an F- cell, which of the following is most likely to occur?

Accepted Answer

The F- cell may acquire new chromosomal genes but usually remains F- because the entire F factor is rarely transferred.

Question 4

Which process of lateral gene transfer involves uptake of naked DNA from the environment by a competent bacterial cell?

Accepted Answer

Transformation

Question 5

During the lytic cycle of a bacteriophage, which of the following events occurs?

Accepted Answer

The host cell is lysed, releasing new phage particles.

Question 6

Given the following time-of-entry data from an Hfr conjugation experiment: leu+ (10 min), thr+ (15 min), his+ (22 min), and lac+ (30 min), what is the correct gene order?

Accepted Answer

leu – thr – his – lac

Question 7

Which of the following best describes a prototroph?

Accepted Answer

A bacterial strain that can grow on minimal medium because it can synthesize all essential compounds.

Question 8

Which enzyme is responsible for unwinding the DNA double helix during replication?

Accepted Answer

Helicase

Question 9

In DNA, which type of bond connects the 3' carbon of one deoxyribose to the 5' phosphate of the next nucleotide?

Accepted Answer

Phosphodiester bond: $$\mathrm{3'	ext{-}OH\ +\ 5'	ext{-}PO_4$^{2-}\ ightarrow\ phosphodiester\ bond}$$

Question 10

Which of the following is NOT a component required for a standard polymerase chain reaction (PCR)?

Accepted Answer

Single-stranded binding protein

Question 11

During gel electrophoresis of DNA, which factor most directly affects the speed at which DNA fragments move through the gel?

Accepted Answer

The length (number of base pairs) of the DNA fragment

Question 12

Which of the following is a difference between DNA and RNA nucleotides?

Accepted Answer

RNA contains uracil instead of thymine and has a 2' hydroxyl group on the ribose.

Question 13

Which sequence is recognized by the sigma factor during bacterial transcription initiation?

Accepted Answer

Pribnow box ($$\mathrm{-10}$$ consensus sequence): $$\mathrm{TATAAT}$$

Question 14

Which of the following best describes the torpedo model of transcription termination in eukaryotes?

Accepted Answer

A 5' to 3' exonuclease degrades the RNA downstream of the cleavage site, catching up to RNA polymerase II and causing dissociation.

Question 15

A mutation changes a codon from UAU to UAA. What is the result of this mutation?

Accepted Answer

A nonsense mutation, introducing a premature stop codon.

Question 16

During translation, which ribosomal site holds the tRNA carrying the growing polypeptide chain?

Accepted Answer

Peptidyl (P) site

Question 17

Which of the following statements about translation initiation in prokaryotes is correct?

Accepted Answer

The small ribosomal subunit binds to the Shine-Dalgarno sequence on the mRNA.

Question 18

Which of the following posttranslational modifications can target a protein for degradation?

Accepted Answer

Ubiquitination

Question 19

How does codon redundancy and the wobble hypothesis affect the number of tRNAs required by a cell?

Accepted Answer

Fewer tRNAs are needed because some tRNAs can recognize multiple codons due to flexible base pairing at the third codon position.

Question 20

A patient is found to have a mutation in the gene encoding DNA ligase. Which process would be most directly affected in their cells?

Accepted Answer

Joining of Okazaki fragments on the lagging strand during DNA replication.

Genetic Analysis and Mapping in Bacteria and Bacteriophages; DNA Structure and Replication; Transcription and RNA Processing; Translation and the Genetic Code

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