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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2:49 minutes

Problem 21b

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 with overlaps?

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Understand the problem: The poly-AC mRNA sequence (ACACACAC...) is being translated using a hypothetical mechanism that reads the genetic code as doublets with overlaps. This means that the ribosome reads two nucleotides at a time, and each doublet overlaps with the previous one by one nucleotide.

Identify the sequence of doublets: Since the mRNA sequence is ACACACAC..., the overlapping doublets would be: AC, CA, AC, CA, and so on. This pattern repeats throughout the sequence.

Determine the amino acids encoded by each doublet: Use a genetic code table that maps doublets to amino acids (note: this is hypothetical, as the real genetic code uses triplets). For example, if AC codes for one amino acid and CA codes for another, identify these amino acids.

Analyze the pattern of amino acids: Since the sequence alternates between AC and CA, the resulting amino acid sequence would alternate between the amino acids encoded by AC and CA. This creates a repeating pattern.

Summarize the findings: The translation of the poly-AC mRNA sequence using a doublet mechanism with overlaps would produce a repeating pattern of two amino acids, corresponding to the doublets AC and CA.

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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 a set of rules that defines how sequences of nucleotides in DNA and RNA are translated into amino acids, the building blocks of proteins. It consists of codons, which are triplets of nucleotides, each corresponding to a specific amino acid. Understanding the genetic code is essential for predicting the amino acid sequence from a given mRNA.

Translation Mechanism

Translation is the process by which ribosomes synthesize proteins using mRNA as a template. In this context, the mechanism that reads the genetic code as a doublet with overlaps means that the ribosome reads two nucleotides at a time, potentially overlapping the reading frames. This approach can lead to different amino acid sequences than the standard triplet reading.

Overlapping Codons

Overlapping codons occur when the reading frame of the genetic code allows for the same nucleotide sequence to be interpreted in multiple ways. In the case of doublet reading, each pair of nucleotides can form a codon that overlaps with the next, creating a unique pattern of amino acids. This concept is crucial for understanding how variations in reading frames can affect protein synthesis.

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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 quadruplet with overlaps?

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Textbook Question

A quadruplet without overlaps?

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Textbook Question

A triplet with overlaps?

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Textbook Question

A triplet without overlaps?

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Textbook Question

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.

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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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