Textbook Question
What experimental evidence provided the initial insights into the compositions of codons encoding specific amino acids?
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11. Translation
The Genetic Code
1:21 minutesProblem 2b
Textbook Question
In the experiments that deciphered the genetic code, many different synthetic mRNA sequences were tested.
What was the result of studies of synthetic mRNAs composed exclusively of cytosine?
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Understand the context: The genetic code was deciphered by studying how synthetic mRNA sequences direct the synthesis of polypeptides in a cell-free system. Synthetic mRNAs composed of only one type of nucleotide (e.g., cytosine) were used to determine which amino acids were encoded by specific codons.
Recall the codon structure: Codons are sequences of three nucleotides in mRNA that specify an amino acid. For a synthetic mRNA composed exclusively of cytosine (C), the codons would be CCC, CCC, and so on.
Determine the amino acid encoded by the codon CCC: Using the genetic code table, identify the amino acid that corresponds to the codon CCC. This codon is known to encode the amino acid proline (Pro).
Predict the resulting polypeptide: Since the synthetic mRNA is composed entirely of cytosine, the ribosome would repeatedly translate the codon CCC, resulting in a polypeptide chain made entirely of proline residues.
Summarize the findings: The studies of synthetic mRNAs composed exclusively of cytosine demonstrated that the codon CCC specifies the amino acid proline, and the resulting polypeptide would be a homopolymer of proline.
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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 the sequence of nucleotides in mRNA is 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 or a stop signal during protein synthesis.
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Synthetic mRNA
Synthetic mRNA refers to artificially created strands of messenger RNA that can be designed to contain specific sequences of nucleotides. These synthetic mRNAs are used in experiments to study gene expression, protein synthesis, and the effects of different nucleotide compositions on translation.
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Polycytidylic Acid (Poly-C)
Polycytidylic acid, or Poly-C, is a synthetic mRNA composed entirely of cytosine nucleotides. Studies involving Poly-C have shown that it predominantly codes for the amino acid proline during translation, illustrating how the composition of mRNA influences the resulting protein synthesis.
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