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Ch. 9 - The Molecular Biology of Translation
Sanders - Genetic Analysis: An Integrated Approach 3rd Edition
Sanders3rd EditionGenetic Analysis: An Integrated ApproachISBN: 9780135564172Not the one you use?Change textbook
Chapter 9, Problem 21f

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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1
Understand the problem: The poly-AC mRNA sequence (ACACACAC...) is being translated using a mechanism that reads the genetic code in quadruplets with overlaps. This means that each codon consists of four nucleotides, and the reading frame shifts by one nucleotide for each new codon.
Write out the sequence of the mRNA: The sequence is repetitive, so it can be represented as ACACACAC... for simplicity. Focus on the first few nucleotides to identify the overlapping quadruplets.
Determine the overlapping quadruplets: Start with the first four nucleotides (ACAC), then shift by one nucleotide to get the next quadruplet (CACA), and so on. The overlapping codons will be ACAC, CACA, ACAC, CACA, etc.
Translate each quadruplet into amino acids: Use the genetic code to determine the amino acid sequence for each quadruplet. Note that the genetic code is typically based on triplets, so you may need to consider how the quadruplet code is interpreted (e.g., by experimental rules or assumptions).
Identify the repeating pattern: Since the sequence is repetitive and the reading frame overlaps, the resulting amino acid sequence will also exhibit a repeating pattern. Analyze the translated amino acids to determine this pattern.

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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 mRNA are translated into amino acids. It consists of codons, which are triplets of nucleotides, each corresponding to a specific amino acid or a stop signal during protein synthesis. Understanding the genetic code is essential for predicting the amino acid sequence from an mRNA template.
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Quadruplet Codons

Quadruplet codons refer to a hypothetical system where four nucleotides are read together as a single unit, rather than the standard triplet codons. This approach would change the way amino acids are encoded, potentially allowing for a different set of amino acids to be produced from the same mRNA sequence. It is important to consider how overlapping reading frames can affect the resulting protein structure.
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Overlapping Genes

Overlapping genes occur when two or more genes share some of the same nucleotide sequences, allowing for multiple proteins to be encoded within the same stretch of DNA or RNA. In the context of reading the genetic code with overlaps, this means that the same sequence can be interpreted in different ways, leading to various amino acid sequences depending on the starting point of the reading frame.
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Segmentation Genes