Ch. 13 - The Genetic Code and Transcription

Klug - Concepts of Genetics 12th Edition

Klug12th EditionConcepts of Genetics ISBN: 9780135564776Not the one you use?Change textbook

Klug 12th Edition

Ch. 13 - The Genetic Code and Transcription

Problem 1d

Chapter 13, Problem 1d

How were the experimentally derived triplet codon assignments verified in studies using bacteriophage MS2?

Verified step by step guidance

Understand that the bacteriophage MS2 system was used to experimentally verify the genetic code by synthesizing RNA sequences with known nucleotide compositions and observing the resulting polypeptides.

Recognize that researchers created synthetic RNA molecules with repeating triplet sequences (e.g., repeating codons like UUU, AAA, or CCC) and introduced these RNAs into a cell-free translation system derived from bacteriophage MS2-infected cells.

Observe the polypeptides produced from these synthetic RNAs, identifying the amino acids incorporated by analyzing the protein products, often using techniques like chromatography or electrophoresis.

Correlate the known synthetic RNA triplet sequences with the amino acid sequences of the resulting polypeptides to confirm which triplet codons specify which amino acids.

Use this experimental approach to systematically verify the assignments of triplet codons to amino acids, thereby confirming the genetic code as deciphered from earlier experiments.

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Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

Triplet Codon Hypothesis

The triplet codon hypothesis states that genetic information is encoded in sequences of three nucleotides, called codons, each specifying a single amino acid. This concept is fundamental to understanding how nucleotide sequences translate into proteins.

Bacteriophage MS2 as a Model System

Bacteriophage MS2 is an RNA virus used as a model to study genetic coding because its genome is well-characterized and simple. Experiments with MS2 allowed researchers to link specific RNA sequences to amino acid sequences, facilitating verification of codon assignments.

Experimental Verification via Mutagenesis and Protein Analysis

Verification involved inducing mutations in the MS2 RNA and analyzing resulting changes in the viral proteins. By correlating specific nucleotide changes with altered amino acids, researchers confirmed the triplet nature of codons and their assignments.

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Related Practice

Textbook Question

How were the specific sequences of triplet codes determined experimentally?

Textbook Question

Assuming the genetic code is a triplet, what effect would the addition or loss of two nucleotides have on the reading frame? The addition or loss of three, six, or nine nucleotides?

Textbook Question

Why did geneticists believe, even before direct experimental evidence was obtained, that the genetic code would turn out to be composed of triplet sequences and be nonoverlapping? Experimentally, how were these suppositions shown to be correct?

Textbook Question

The mRNA formed from the repeating tetranucleotide UUAC incorporates only three amino acids, but the use of UAUC incorporates four amino acids. Why?

Textbook Question

Write a short essay that summarizes the key properties of the genetic code and the process by which RNA is transcribed on a DNA template.

Textbook Question

What experimental evidence provided the initial insights into the compositions of codons encoding specific amino acids?

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