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Ch. 12 - The Genetic Code and Transcription
Klug - Essentials of Genetics 10th Edition
Klug10th EditionEssentials of GeneticsISBN: 9780135588789Not the one you use?Change textbook
All textbooksKlug 10th EditionCh. 12 - The Genetic Code and TranscriptionProblem 22
Chapter 12, Problem 22

In a mixed copolymer experiment, messages were created with either 4/5C:1/5A or 4/5A:1/5C. These messages yielded proteins with the following amino acid compositions.
Table showing amino acid yields from mixed copolymer experiments in genetics.
Using these data, predict the most specific coding composition for each amino acid.

Verified step by step guidance
1
Step 1: Understand the experimental setup. Two mixed copolymers were used: one with 4/5 Cytosine (C) and 1/5 Adenine (A), and the other with 4/5 Adenine (A) and 1/5 Cytosine (C). These mixtures were used to synthesize proteins, and the amino acid yields were measured.
Step 2: Analyze the amino acid yields for each copolymer. For each amino acid, compare the yield from the 4/5C:1/5A mixture to the yield from the 4/5A:1/5C mixture. Amino acids with high yield in the 4/5C:1/5A mixture and low yield in the 4/5A:1/5C mixture are likely coded by codons rich in Cytosine. Conversely, amino acids with high yield in the 4/5A:1/5C mixture and low yield in the 4/5C:1/5A mixture are likely coded by codons rich in Adenine.
Step 3: For amino acids with similar yields in both mixtures (like Threonine), infer that their codons likely contain a balanced or mixed composition of C and A, or that the codon position being tested is not specific to either base.
Step 4: Use the relative yields to predict the most specific coding composition for each amino acid. For example, Proline has a high yield (63.0%) in the 4/5C:1/5A mixture and very low (3.5%) in the 4/5A:1/5C mixture, suggesting Proline codons are rich in Cytosine. Lysine shows the opposite pattern, indicating codons rich in Adenine.
Step 5: Summarize the predictions by assigning each amino acid to the base composition (C or A) that corresponds to its higher yield, thus identifying the most specific coding composition for each amino acid based on the experimental data.

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Key Concepts

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

Mixed Copolymer Experiment

A mixed copolymer experiment involves synthesizing RNA sequences with known ratios of nucleotides to determine which amino acids are encoded by specific nucleotide combinations. By analyzing the resulting protein composition, researchers can infer the codon assignments for amino acids based on the frequency of nucleotides in the RNA.
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Mendel's Experiments

Codon-Amino Acid Specificity

Codon specificity refers to the relationship between a sequence of three nucleotides (codon) in mRNA and the amino acid it encodes. In mixed copolymer experiments, the relative abundance of amino acids produced from different nucleotide ratios helps identify which codons correspond to which amino acids, revealing the genetic code.
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Interpreting Amino Acid Yield Data

Amino acid yield data from mixed copolymer experiments show the percentage of each amino acid produced under different nucleotide ratios. High yield of an amino acid in one mixture and low in another suggests that the amino acid is encoded by codons rich in the predominant nucleotide of that mixture, allowing prediction of codon composition.
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History and Experiments
Related Practice
Textbook Question

Write a paragraph describing the abbreviated chemical reactions that summarize RNA polymerase-directed transcription.

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Textbook Question

Messenger RNA molecules are very difficult to isolate in bacteria because they are rather quickly degraded in the cell. Can you suggest a reason why this occurs? Eukaryotic mRNAs are more stable and exist longer in the cell than do bacterial mRNAs. Is this an advantage or a disadvantage for a pancreatic cell making large quantities of insulin?

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Textbook Question

One form of posttranscriptional modification of most eukaryotic pre-mRNAs is the addition of a poly-A sequence at the 3' end. The absence of a poly-A sequence leads to rapid degradation of the transcript. Poly-A sequences of various lengths are also added to many bacterial RNA transcripts where, instead of promoting stability, they enhance degradation. In both cases, RNA secondary structures, stabilizing proteins, or degrading enzymes interact with poly-A sequences. Considering the activities of RNAs, what might be general functions of 3'-polyadenylation?

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Textbook Question

Shown here are the amino acid sequences of the wild-type and three mutant forms of a short protein.

___________________________________________________

Wild-type: Met-Trp-Tyr-Arg-Gly-Ser-Pro-Thr

Mutant 1: Met-Trp

Mutant 2: Met-Trp-His-Arg-Gly-Ser-Pro-Thr

Mutant 3: Met-Cys-Ile-Val-Val-Val-Gln-His                 _


Use this information to answer the following questions:

Using the genetic coding dictionary, predict the type of mutation that led to each altered protein.

1047
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Textbook Question

Shown here are the amino acid sequences of the wild-type and three mutant forms of a short protein.

___________________________________________________

Wild-type: Met-Trp-Tyr-Arg-Gly-Ser-Pro-Thr

Mutant 1: Met-Trp

Mutant 2: Met-Trp-His-Arg-Gly-Ser-Pro-Thr

Mutant 3: Met-Cys-Ile-Val-Val-Val-Gln-Hi

___________________________________________________

Use this information to answer the following questions:

For each mutant protein, determine the specific ribonucleotide change that led to its synthesis.

478
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Textbook Question

Shown here are the amino acid sequences of the wild-type and three mutant forms of a short protein.

__________________________________________________

Wild-type: Met-Trp-Tyr-Arg-Gly-Ser-Pro-Thr

Mutant 1: Met-Trp

Mutant 2: Met-Trp-His-Arg-Gly-Ser-Pro-Thr

Mutant 3: Met -Cys-Ile-Val-Val-Val-Gln-His

______________________________________________

Use this information to answer the following questions:

The wild-type RNA consists of nine triplets. What is the role of the ninth triplet?

500
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