Q: A segment of DNA has the following sequence on the coding strand: 5'-ATG GGC TTT-3'. What is the corresponding mRNA sequence?

$$5'\text{-}AUG\ GGC\ UUU\text{-}3'$$

Question 1

Which experimental approach did Beadle and Tatum use to demonstrate the relationship between genes and enzymes in Neurospora crassa?

Accepted Answer

They exposed Neurospora cells to X-rays to induce mutations and screened for nutritional mutants.

Question 2

In the metabolic pathway for arginine synthesis in Neurospora, a mutant that grows only when citrulline or arginine is added to the medium but not with ornithine is most likely defective in which enzyme?

Accepted Answer

Enzyme B (converts ornithine to citrulline)

Question 3

Which statement best describes the central dogma of molecular biology?

Accepted Answer

DNA is transcribed into RNA, which is then translated into protein.

Question 4

A mutation in the gene encoding tyrosinase leads to albinism in donkeys. What is the molecular basis for this phenotype?

Accepted Answer

The mutation prevents the synthesis of melanin by producing a nonfunctional enzyme.

Question 5

Which of the following best explains why the genetic code is described as redundant but not ambiguous?

Accepted Answer

Multiple codons can specify the same amino acid, but each codon specifies only one amino acid.

Question 6

In eukaryotic cells, what is the correct sequence of events for gene expression from a protein-coding gene?

Accepted Answer

Transcription → RNA processing → Translation

Question 7

A segment of DNA has the following sequence on the coding strand: 5'-ATG GGC TTT-3'. What is the corresponding mRNA sequence?

Accepted Answer

$$5'	ext{-}AUG\ GGC\ UUU	ext{-}3'$$

Question 8

Which of the following is a direct result of alternative splicing in eukaryotic gene expression?

Accepted Answer

A single gene can code for multiple related polypeptides.

Question 9

Why can translation of mRNA begin before transcription is finished in bacteria but not in eukaryotes?

Accepted Answer

Bacteria lack a nuclear envelope, so transcription and translation are not separated.

Question 10

A mutation changes the DNA sequence from 5'-GAA-3' to 5'-GAG-3'. Both codons specify glutamic acid. What is this type of mutation called?

Accepted Answer

Silent mutation

Question 11

Which of the following best illustrates the evolutionary significance of the nearly universal genetic code?

Accepted Answer

It allows genes from one species to be expressed in another species.

Question 12

If a Neurospora mutant cannot grow on minimal medium but grows when supplemented with arginine, what does this indicate about the mutant?

Accepted Answer

It lacks the enzyme required to synthesize arginine.

Question 13

Which of the following is NOT a difference between DNA and RNA?

Accepted Answer

DNA is translated into protein; RNA is transcribed from protein.

Question 14

A patient with alkaptonuria excretes black urine due to the accumulation of alkapton. According to Garrod's hypothesis, what is the most likely cause?

Accepted Answer

A mutation in a gene encoding an enzyme that breaks down alkapton.

Question 15

Given the mRNA codon table, what amino acid is specified by the codon $$5'	ext{-}AUG	ext{-}3'$$?

Accepted Answer

Methionine (Met)

Question 16

Which process is responsible for converting the information in mRNA into a sequence of amino acids?

Accepted Answer

Translation

Question 17

If the reading frame of an mRNA is shifted by the insertion of a single nucleotide, what is the likely result?

Accepted Answer

A frameshift mutation, altering all downstream amino acids.

Question 18

Which of the following best describes the role of messenger RNA (mRNA) in gene expression?

Accepted Answer

It carries the genetic message from DNA to the protein-synthesizing machinery.

Gene Expression: From Gene to Protein – Transcription, Translation, and the Genetic Code

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