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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
All textbooksSanders 3rd EditionCh. 9 - The Molecular Biology of TranslationProblem 2a
Chapter 9, Problem 2a

In the experiments that deciphered the genetic code, many different synthetic mRNA sequences were tested.
Describe how the codon for phenylalanine was identified.

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1
Understand the context: The genetic code was deciphered using synthetic mRNA sequences in experiments conducted by researchers like Nirenberg and Matthaei. These experiments aimed to determine which codons correspond to specific amino acids.
Recognize the experimental setup: In the case of phenylalanine, a synthetic mRNA sequence composed entirely of uracil nucleotides (poly-U) was synthesized. This sequence would look like UUUUUU... (repeating U bases).
Explain the translation process: The synthetic poly-U mRNA was added to a cell-free system containing ribosomes, tRNAs, and amino acids, where one of the amino acids was radioactively labeled to track its incorporation into a protein.
Describe the observation: When the poly-U mRNA was used, the radioactive phenylalanine was incorporated into the protein, indicating that the codon UUU specifies phenylalanine.
Conclude the finding: This experiment demonstrated that the codon UUU in mRNA corresponds to the amino acid phenylalanine, contributing to the understanding of the genetic code.

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Key Concepts

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

Codons

Codons are sequences of three nucleotides in mRNA that correspond to specific amino acids or stop signals during protein synthesis. Each codon is crucial for translating the genetic information encoded in DNA into functional proteins. Understanding codons is essential for deciphering how genetic information is expressed and how specific amino acids, like phenylalanine, are incorporated into proteins.
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The Genetic Code

Synthetic mRNA

Synthetic mRNA refers to artificially created messenger RNA sequences used in experiments to study the genetic code. By introducing these synthetic mRNAs into a system, researchers can observe which amino acids are produced, allowing them to determine the relationship between specific codons and their corresponding amino acids. This method was pivotal in identifying the codon for phenylalanine.
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Amino Acid Translation

Amino acid translation is the process by which the sequence of codons in mRNA is translated into a sequence of amino acids, forming a protein. This process occurs during translation, where ribosomes read the mRNA and tRNA molecules bring the appropriate amino acids. Identifying the codon for phenylalanine involved determining which specific codon sequence led to the incorporation of phenylalanine into the growing polypeptide chain.
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Related Practice
Textbook Question

Some proteins are composed of two or more polypeptides. Suppose the DNA template strand sequence 3′-TACGTAGGCTAACGGAGTAAGCTAACT-5′ produces a polypeptide that joins in pairs to form a functional protein.

What term is used to identify a functional protein like this one formed when two identical polypeptides join together?

Textbook Question

Homocystinuria is a rare autosomal recessive condition on the RUSP list of conditions screened by newborn genetic testing. The condition results from a mutation that blocks the degradation of the amino acid methionine. The absence of a critical enzyme causes the buildup of the compound homocysteine, which is one of the intermediate compounds in the methionine breakdown pathway. Homocystinuria causes mental impairment, heart problems, seizures, eye abnormalities, and a number of other symptoms that shorten life if not treated. The condition is treated by a specialized diet that is low in methionine and by the ingestion of several supplements.

The low-methionine diet must be maintained throughout life to manage homocystinuria. Why do you think this is the case?

Textbook Question

Homocystinuria is a rare autosomal recessive condition on the RUSP list of conditions screened by newborn genetic testing. The condition results from a mutation that blocks the degradation of the amino acid methionine. The absence of a critical enzyme causes the buildup of the compound homocysteine, which is one of the intermediate compounds in the methionine breakdown pathway. Homocystinuria causes mental impairment, heart problems, seizures, eye abnormalities, and a number of other symptoms that shorten life if not treated. The condition is treated by a specialized diet that is low in methionine and by the ingestion of several supplements.

Why do you think eating a low-methionine diet is critical to controlling homocystinuria?

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?

Textbook Question

In the experiments that deciphered the genetic code, many different synthetic mRNA sequences were tested.

What result was obtained for synthetic mRNAs containing AG repeats, that is, AGAGAGAG...?

Textbook Question

In the experiments that deciphered the genetic code, many different synthetic mRNA sequences were tested.

Predict the results of experiments examining GCUA repeats.