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Ch. 14 - Translation and Proteins
Klug - Concepts of Genetics  12th Edition
Klug12th EditionConcepts of Genetics ISBN: 9780135564776Not the one you use?Change textbook
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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