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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1:28 minutes

Problem 24d

Textbook Question

Har Gobind Khorana and his colleagues performed numerous experiments translating synthetic mRNAs. In one experiment, an mRNA molecule with a repeating UG dinucleotide sequence was assembled and translated.
If the genetic code were a doublet code instead of a triplet code, how would the result of this experiment be different?

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Understand the concept of the genetic code: The genetic code is a triplet code, meaning that three nucleotides (codons) specify one amino acid. If the code were a doublet code, only two nucleotides would specify one amino acid, reducing the number of possible codons.

Analyze the repeating UG dinucleotide sequence: The mRNA sequence in the experiment alternates between U and G, forming a repeating pattern (UGUGUG...). In a triplet code, codons would be read in groups of three nucleotides, such as UGU, GUG, etc. In a doublet code, codons would be read in groups of two nucleotides, such as UG, GU, etc.

Determine the implications of a doublet code: A doublet code would result in fewer possible codons (4^2 = 16 codons) compared to a triplet code (4^3 = 64 codons). This would limit the diversity of amino acids that could be encoded, as there are 20 amino acids in the standard genetic code.

Predict the translation outcome: In a doublet code scenario, the repeating UG sequence would produce fewer distinct codons, potentially leading to a simpler or repetitive polypeptide sequence. For example, UG and GU might correspond to fewer amino acids, resulting in a less complex protein.

Compare to the triplet code result: In the actual experiment with a triplet code, the repeating UG sequence would produce a more diverse set of codons and a more complex polypeptide. This highlights the importance of the triplet code in encoding the full range of amino acids and generating functional proteins.

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Key Concepts

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

Genetic Code

The genetic code is the set of rules by which information encoded in genetic material is translated into proteins. It consists of codons, which are sequences of three nucleotides that correspond to specific amino acids. Understanding the genetic code is crucial for interpreting how mRNA sequences are translated into proteins.

Triplet Code vs. Doublet Code

The triplet code refers to the use of three nucleotides (codons) to specify each amino acid in protein synthesis, allowing for 64 possible combinations. In contrast, a doublet code would use pairs of nucleotides, resulting in only 16 combinations. This difference significantly impacts the diversity of proteins that can be synthesized from mRNA.

Translation Process

Translation is the process by which ribosomes synthesize proteins using mRNA as a template. During translation, the ribosome reads the mRNA codons and assembles the corresponding amino acids into a polypeptide chain. The efficiency and accuracy of translation depend on the structure of the genetic code, which determines how sequences are interpreted.

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Related Practice

Textbook Question

In an experiment to decipher the genetic code, a poly-AC mRNA (ACACACAC...) is synthesized. What pattern of amino acids would appear if this sequence were to be translated by a mechanism that reads the genetic code as

A doublet without overlaps?

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Textbook Question

The amino acid sequence of a portion of a polypeptide is

N...Cys-Pro-Ala-Met-Gly-His-Lys...C

Give the DNA template and coding strand sequences corresponding to the mRNA. Use the N, Pu, and Py symbols as placeholders.

627

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Textbook Question

The amino acid sequence of a portion of a polypeptide is

N...Cys-Pro-Ala-Met-Gly-His-Lys...C

What is the mRNA sequence encoding this polypeptide fragment? Use N to represent any nucleotide, Pu to represent a purine, and Py to represent a pyrimidine. Label the 5′ and 3′ ends of the mRNA.

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Textbook Question

Har Gobind Khorana and his colleagues performed numerous experiments translating synthetic mRNAs. In one experiment, an mRNA molecule with a repeating UG dinucleotide sequence was assembled and translated.

If the genetic code were overlapping rather than nonoverlapping, how would the result of this experiment be different?

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Textbook Question

How did the polypeptide composition help confirm the triplet nature of the genetic code?

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Textbook Question

What is the sequence of the resulting polypeptide?

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Textbook Question