Textbook Question
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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11. Translation
The Genetic Code
2:16 minutesProblem 4
Textbook Question
The mRNA formed from the repeating tetranucleotide UUAC incorporates only three amino acids, but the use of UAUC incorporates four amino acids. Why?
Verified step by step guidance1
Understand the problem: The question is asking why the mRNA sequence UUAC results in only three amino acids, while UAUC results in four amino acids. This involves understanding the genetic code and how codons (triplets of nucleotides) are translated into amino acids.
Recall the concept of codons: Each codon is a sequence of three nucleotides in mRNA that corresponds to a specific amino acid or a stop signal during translation. The repeating tetranucleotide sequence UUAC or UAUC will be read in overlapping triplets by the ribosome.
Analyze the sequence UUAC: When the ribosome reads the repeating sequence UUAC, the possible codons formed are UUA, UAC, ACU, and CUU. However, due to the repeating nature of the sequence, some codons may overlap or repeat, limiting the diversity of amino acids produced.
Analyze the sequence UAUC: For the repeating sequence UAUC, the possible codons formed are UAU, AUC, UCA, and CUA. This sequence allows for four distinct codons, each potentially coding for a different amino acid, increasing the diversity of amino acids produced compared to UUAC.
Conclude the reasoning: The difference in the number of amino acids incorporated arises from the specific arrangement of nucleotides in the tetranucleotide sequence. UUAC produces fewer distinct codons due to overlapping and repetition, while UAUC produces more distinct codons, allowing for four amino acids to be incorporated.
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Key Concepts
Here are the essential concepts you must grasp in order to answer the question correctly.
Tetranucleotide Structure
A tetranucleotide consists of four nucleotides in a specific sequence. In the context of mRNA, the sequence of nucleotides determines the codons, which are groups of three nucleotides that code for specific amino acids. The arrangement of these nucleotides affects how many unique codons can be formed, influencing the number of amino acids incorporated during protein synthesis.
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Codon Usage
Codons are sequences of three nucleotides in mRNA that correspond to specific amino acids during translation. The genetic code is degenerate, meaning that multiple codons can code for the same amino acid. The difference in the number of amino acids incorporated from the two tetranucleotides arises from the specific codons generated by their sequences, affecting the overall protein structure.
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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 matches them with the appropriate tRNA molecules that carry amino acids. The efficiency and outcome of translation depend on the mRNA sequence, which dictates how many and which amino acids are added to the growing polypeptide chain.
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