Francis Crick proposed the 'adaptor hypothesis' for the function of tRNA. Why did he choose that description?
Ch. 14 - Translation and Proteins

Chapter 14, Problem 7
Assuming that each nucleotide in an mRNA is 0.34 nm long, how many triplet codes can simultaneously occupy the space in a ribosome that is 20 nm in diameter?
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Understand the problem: We need to find how many triplet codons (each consisting of 3 nucleotides) can fit within the length of the ribosome, which is given as 20 nm in diameter. Each nucleotide is 0.34 nm long, so the total length occupied by a triplet codon is 3 times 0.34 nm.
Calculate the length of one triplet codon by multiplying the length of a single nucleotide by 3: \$3 \times 0.34 \text{ nm}$.
Determine how many such triplet codons can fit into the 20 nm space by dividing the total length of the ribosome (20 nm) by the length of one triplet codon: \(\frac{20 \text{ nm}}{3 \times 0.34 \text{ nm}}\).
Interpret the result as the number of triplet codons that can simultaneously occupy the ribosome space. Since the number of codons must be a whole number, consider whether to round down to the nearest whole number.
Summarize the approach: by dividing the ribosome length by the length of one codon, you find the maximum number of codons that can fit simultaneously in the ribosome.

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Key Concepts
Here are the essential concepts you must grasp in order to answer the question correctly.
Structure and Length of mRNA Nucleotides
mRNA is composed of nucleotides arranged linearly, each approximately 0.34 nm in length. This measurement helps determine how much physical space a sequence of nucleotides occupies, which is essential for calculating how many codons fit within a given length.
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Triplet Codon Concept in Genetic Code
A triplet codon consists of three consecutive nucleotides in mRNA that encode a specific amino acid during protein synthesis. Understanding that codons are groups of three nucleotides is crucial for relating nucleotide length to the number of codons present.
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Physical Constraints of the Ribosome
The ribosome is a molecular machine with a defined size, here given as 20 nm in diameter. Knowing the ribosome's spatial dimensions allows us to estimate how many nucleotides or codons can physically fit inside its active site during translation.
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Related Practice
Textbook Question
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Textbook Question
During translation, what molecule bears the codon? the anticodon?
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Textbook Question
The α chain of eukaryotic hemoglobin is composed of 141 amino acids. What is the minimum number of nucleotides in an mRNA coding for this polypeptide chain?
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Textbook Question
Summarize the steps involved in charging tRNAs with their appropriate amino acids.
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Textbook Question
To carry out its role, each transfer RNA requires at least four specific recognition sites that must be inherent in its tertiary structure. What are they?
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Textbook Question
What are isoaccepting tRNAs? Assuming that there are only 20 different aminoacyl tRNA synthetases but 31 different tRNAs, speculate on parameters that might be used to ensure that each charged tRNA has received the correct amino acid.
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