Q: A gene sequence is 5'-ATG GAA TGC TAA-3'. What is the corresponding mRNA sequence transcribed from this DNA (assume the coding strand is shown)?

$$5'\text{-}AUG\ GAA\ UGC\ UAA\text{-}3'$$

Question 1

A patient’s mitochondrial DNA is found to translate the codon UGA as tryptophan, rather than as a stop signal. What does this observation best illustrate about the genetic code?

Accepted Answer

There are exceptions to the universality of the genetic code.

Question 2

A gene sequence is 5'-ATG GAA TGC TAA-3'. What is the corresponding mRNA sequence transcribed from this DNA (assume the coding strand is shown)?

Accepted Answer

$$5'	ext{-}AUG\ GAA\ UGC\ UAA	ext{-}3'$$

Question 3

Which of the following best explains why a single base insertion near the start of a gene often results in a nonfunctional protein?

Accepted Answer

It causes a frameshift mutation, altering all downstream codons.

Question 4

A researcher mutates the Pribnow box in a bacterial promoter. What is the most likely effect on transcription?

Accepted Answer

RNA polymerase will have difficulty binding, reducing transcription initiation.

Question 5

Which of the following statements about the wobble hypothesis is correct?

Accepted Answer

The third base of the codon allows non-standard pairing, enabling one tRNA to recognize multiple codons.

Question 6

During eukaryotic mRNA processing, which of the following modifications increases mRNA stability and facilitates export from the nucleus?

Accepted Answer

Addition of a 5' cap and a poly-A tail

Question 7

A scientist discovers a single mRNA that produces two different proteins in a virus. What genetic phenomenon does this most likely represent?

Accepted Answer

Overlapping genes with different reading frames

Question 8

Which of the following best describes the direction in which RNA polymerase synthesizes RNA?

Accepted Answer

$$5' \rightarrow 3'$$

Question 9

A mutation changes a codon from UAU (tyrosine) to UAA. What type of mutation is this, and what is its likely effect?

Accepted Answer

Nonsense mutation; introduces a premature stop codon

Question 10

Which of the following is NOT a feature of the genetic code?

Accepted Answer

It is overlapping, with each nucleotide part of multiple codons.

Question 11

A prokaryotic gene is transcribed, but the resulting mRNA is not translated into protein. Analysis reveals a mutation in the rho protein. Which process is most likely affected?

Accepted Answer

Rho-dependent transcription termination

Question 12

Which of the following best explains why the genetic code is described as 'colinear'?

Accepted Answer

The sequence of codons in the gene directly corresponds to the sequence of amino acids in the protein.

Question 13

A eukaryotic cell is exposed to a toxin that inhibits the addition of the 5' cap to pre-mRNA. Which of the following is a likely consequence?

Accepted Answer

The mRNA will be rapidly degraded and not efficiently translated.

Question 14

Which of the following is a key difference between prokaryotic and eukaryotic transcription?

Accepted Answer

Eukaryotic transcription requires transcription factors, while prokaryotic transcription does not.

Question 15

A mutation in a eukaryotic gene prevents the removal of introns. What is the most likely result?

Accepted Answer

The mature mRNA will contain non-coding sequences, potentially leading to a nonfunctional protein.

Question 16

Which of the following best describes the function of the sigma factor in prokaryotic transcription?

Accepted Answer

It recognizes and binds to the promoter region to initiate transcription.

Question 17

A scientist is studying a gene with the following mRNA sequence: 5'-AUG GCU UGA CCA-3'. Which amino acids are encoded before translation terminates?

Accepted Answer

Methionine, Alanine

Question 18

Which of the following processes can result in the production of different proteins from the same pre-mRNA in eukaryotes?

Accepted Answer

Alternative splicing

Question 19

A patient’s cells are found to have mRNAs with incorrect nucleotide sequences due to post-transcriptional changes. Which process is most likely responsible?

Accepted Answer

RNA editing

Question 20

A mutation changes the sequence of a gene from 5'-ATG GAA TGC TAA-3' to 5'-ATG GAA TGC TGA-3'. What is the effect of this mutation if the gene is in human nuclear DNA?

Accepted Answer

The stop codon is changed, but since TGA is also a stop codon in nuclear DNA, translation will still terminate at the same position.

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