Table of contents

1. Introduction to Genetics51m
2. Mendel's Laws of Inheritance3h 37m
3. Extensions to Mendelian Inheritance2h 41m
4. Genetic Mapping and Linkage2h 28m
5. Genetics of Bacteria and Viruses1h 21m
6. Chromosomal Variation1h 48m
7. DNA and Chromosome Structure56m
8. DNA Replication1h 10m
9. Mitosis and Meiosis1h 34m
10. Transcription1h 0m
11. Translation58m
12. Gene Regulation in Prokaryotes1h 19m
13. Gene Regulation in Eukaryotes44m
14. Genetic Control of Development44m
15. Genomes and Genomics1h 50m
16. Transposable Elements47m
17. Mutation, Repair, and Recombination1h 6m
18. Molecular Genetic Tools19m
- Genetic Cloning
  9m
- Methods for Analyzing DNA
  9m
19. Cancer Genetics29m
- Overview of Cancer
  21m
- Cancer Mutations
  7m
20. Quantitative Genetics1h 26m
21. Population Genetics50m
- Hardy Weinberg
  19m
- Allelic Frequency Changes
  31m
22. Evolutionary Genetics29m

11. Translation

The Genetic Code

Genetics

11. Translation

The Genetic Code

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2:21 minutes

Problem 28

Textbook Question

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.

Using these data, predict the most specific coding composition for each amino acid.

Verified step by step guidance

Step 1: Understand the experimental setup. Two mixed copolymers were synthesized with different ratios of nucleotides: 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 copolymers were translated into 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 in the 4/5C:1/5A mixture versus the 4/5A:1/5C mixture. Amino acids with high yield in one mixture and low yield in the other suggest a strong association with the predominant nucleotide in that mixture.

Step 3: Assign the most specific coding composition for each amino acid based on the yield differences. For example, Proline has a high yield (63.0%) in the 4/5C:1/5A mixture and a low yield (3.5%) in the 4/5A:1/5C mixture, indicating that Proline is likely coded by codons rich in Cytosine (C). Conversely, Lysine shows the opposite pattern, suggesting it is coded by codons rich in Adenine (A).

Step 4: For amino acids with similar yields in both mixtures (e.g., Threonine with 16.0% and 16.6%), infer that their codons likely contain a balanced composition of C and A or are less influenced by the nucleotide ratio in the copolymer.

Step 5: Summarize the predicted coding compositions by grouping amino acids according to their predominant nucleotide association, using the yield data as evidence. This approach helps deduce which nucleotides are most critical in the codons for each amino acid.

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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 produce proteins. By analyzing the amino acid composition of the resulting proteins, researchers can infer which codons correspond to specific amino acids. This method was crucial in early genetic code deciphering.

Codon-Amino Acid Specificity

Each amino acid is encoded by one or more specific codons, sequences of three nucleotides. The frequency of amino acids produced in mixed copolymer experiments reflects the nucleotide composition of the codons, allowing prediction of which codons code for which amino acids based on yield differences.

Nucleotide Composition and Protein Yield Correlation

The relative abundance of nucleotides in the synthetic RNA influences the frequency of codons and thus the amino acids incorporated into proteins. Comparing amino acid yields from different nucleotide ratios helps identify the nucleotide composition of codons for each amino acid by correlating high yields with dominant nucleotides.

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Textbook Question

It has been suggested that the present-day triplet genetic code evolved from a doublet code when there were fewer amino acids available for primitive protein synthesis.

The amino acids Ala, Val, Gly, Asp, and Glu are all early members of biosynthetic pathways and are more evolutionarily conserved than other amino acids. They therefore probably represent 'early' amino acids. Of what significance is this information in terms of the evolution of the genetic code? Also, which base, of the first two within a coding triplet, would likely have been the more significant in originally specifying these amino acids?

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Textbook Question

It has been suggested that the present-day triplet genetic code evolved from a doublet code when there were fewer amino acids available for primitive protein synthesis.

Can you find any support for the doublet code notion in the existing coding dictionary?

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Textbook Question

The mature mRNA transcribed from the human β-globin gene is considerably longer than the sequence needed to encode the 146–amino acid polypeptide. Give the names of three sequences located on the mature β-globin mRNA but not translated.

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Textbook Question

An early proposal by George Gamow in 1954 regarding the genetic code considered the possibility that DNA served directly as the template for polypeptide synthesis. In eukaryotes, what difficulties would such a system pose? What observations and theoretical considerations argue against such a proposal?

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Textbook Question

Recombinant human insulin (made by inserting human DNA encoding insulin into E. coli) is one of the most widely used recombinant pharmaceutical products in the world. What segments of the human insulin gene are used to create recombinant bacteria that produce human insulin?

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Textbook Question

Explain why it is not feasible to insert the entire human insulin gene into E. coli and anticipate the production of insulin.

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Textbook Question

A research scientist is interested in producing human insulin in the bacterial species E. coli. Will the genetic code allow the production of human proteins from bacterial cells? Explain why or why not.

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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.

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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

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Use this information to answer the following questions:

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