Q: Which statement best describes the central dogma of molecular biology?

$$\text{DNA} \rightarrow \text{RNA} \rightarrow \text{Protein}$$

Question 1

Which experimental organism did Beadle and Tatum use to demonstrate the one gene–one enzyme hypothesis, and what was a key advantage of this organism for their experiments?

Accepted Answer

Neurospora crassa; it is haploid so only one allele needs to be mutated to see an effect.

Question 2

A Neurospora mutant can grow on minimal medium supplemented with citrulline or arginine, but not with ornithine. Based on the pathway Precursor → Ornithine → Citrulline → Arginine, which enzyme is likely defective in this mutant?

Accepted Answer

Enzyme B (converts Ornithine to Citrulline)

Question 3

Which statement best describes the central dogma of molecular biology?

Accepted Answer

$$	ext{DNA} ightarrow 	ext{RNA} ightarrow 	ext{Protein}$$

Question 4

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 5

A segment of DNA has the template strand sequence 3'-TACGGTGAA-5'. What is the corresponding mRNA sequence (5' to 3') transcribed from this template?

Accepted Answer

5'-AUGCCACUU-3'

Question 6

Using the genetic code, what polypeptide sequence is produced from the mRNA sequence 5'-AUGUUUGGCUGA-3'?

Accepted Answer

Met-Phe-Gly

Question 7

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 8

In the Beadle and Tatum experiment, why did some Neurospora mutants grow only when a specific amino acid was added to the medium?

Accepted Answer

They lacked the enzyme to synthesize that amino acid due to a gene mutation.

Question 9

Which of the following is a direct product of transcription in eukaryotic cells?

Accepted Answer

Pre-mRNA

Question 10

A mutation changes the DNA sequence from 3'-TAC-5' to 3'-TAA-5' in the template strand. What is the effect on the protein product?

Accepted Answer

The mRNA will code for a stop codon, leading to premature termination of translation.

Question 11

Which process occurs in the cytoplasm of both prokaryotic and eukaryotic cells?

Accepted Answer

Translation

Question 12

Why can bacteria begin translating mRNA before transcription is finished, but eukaryotes cannot?

Accepted Answer

Bacteria do not have a nucleus, so transcription and translation are not separated.

Question 13

A scientist inserts a jellyfish gene into a tobacco plant, and the plant glows under UV light. What does this demonstrate about the genetic code?

Accepted Answer

The genetic code is nearly universal among all organisms.

Question 14

If a eukaryotic gene is transcribed but not properly processed, what is most likely to happen?

Accepted Answer

The pre-mRNA will not be exported from the nucleus and will not be translated.

Question 15

Which of the following best describes the relationship between genotype and phenotype?

Accepted Answer

Genotype determines phenotype by dictating the synthesis of proteins.

Question 16

A patient with alkaptonuria cannot break down alkapton due to a defective enzyme. According to Garrod's hypothesis, what is the genetic basis for this disorder?

Accepted Answer

A mutation in the gene encoding the enzyme that breaks down alkapton.

Question 17

If the mRNA sequence is 5'-GGG GGG GGG GGG GGG GGG GGG GGG GGG GGG-3', what polypeptide will be produced?

Accepted Answer

A polypeptide consisting entirely of glycine residues.

Question 18

Which of the following is true about codons?

Accepted Answer

Each codon specifies a single amino acid or a stop signal.

Question 19

What would be the effect of a frameshift mutation near the start of a gene?

Accepted Answer

It would likely change every amino acid downstream of the mutation.

Gene Expression: From Gene to Protein (Transcription and Translation)

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