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Ch. 16+17 - Transcription, RNA Processing, and Translation
All textbooksFreeman 8th EditionCh. 16+17 - Transcription, RNA Processing, and TranslationProblem 10
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Chapter 16, Problem 10

One of the possibilities considered about the genetic code was that the code was overlapping, meaning that a single base could be part of up to three codons. How many amino acids would be encoded in the sequence 5′-AUGUUACGGAAU-3′ by a non-overlapping and a maximally overlapping triplet code? a. 4 (non-overlapping) and 16 (overlapping) b. 4 and 12 c. 4 and 10 d. 12 and 4

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First, understand the sequence given: 5'-AUGUUACGGAAU-3'. This sequence contains 12 nucleotides.
For the non-overlapping triplet code, divide the sequence into groups of three nucleotides each, starting from the 5' end. This results in four groups: AUG, UUA, CGG, AAU. Each group codes for one amino acid, so there are 4 amino acids encoded.
For the maximally overlapping triplet code, start at the first nucleotide and shift one nucleotide at a time to form a new triplet until reaching the end of the sequence. The first triplet is AUG, the second is UGU, the third is GUU, and so on until the last triplet starting from the tenth nucleotide. This results in 10 triplets, hence encoding 10 amino acids.
Compare the number of amino acids encoded in both methods: 4 amino acids for the non-overlapping code and 10 amino acids for the overlapping code.
The correct answer is option c: 4 (non-overlapping) and 10 (overlapping).

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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 sequences of nucleotides in DNA or RNA are translated into proteins. It consists of codons, which are triplets of nucleotides that correspond to specific amino acids. Understanding the genetic code is essential for determining how many amino acids are encoded by a given nucleotide sequence.
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Genetic Code

Non-overlapping vs. Overlapping Codons

In a non-overlapping genetic code, each nucleotide is part of only one codon, meaning that codons are read sequentially without sharing nucleotides. In contrast, a maximally overlapping code allows a single nucleotide to be part of multiple codons, potentially increasing the number of amino acids encoded. This distinction is crucial for calculating the number of amino acids from a nucleotide sequence.
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Codon Reading Frame

The reading frame refers to the way nucleotides in a sequence are grouped into codons for translation. In a standard triplet code, the reading frame starts from a specific nucleotide and continues in sets of three. Shifting the reading frame can lead to different interpretations of the same nucleotide sequence, affecting the number of amino acids produced in both non-overlapping and overlapping scenarios.
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Textbook Question

The nucleotide shown here is called cordycepin triphosphate. It is a natural product of a fungus that is used in traditional medicines. If cordycepin triphosphate is added to a cell-free transcription reaction, the nucleotide is added onto the growing RNA chain but then no more nucleotides can be added. Examine the structure of cordycepin and explain why it ends transcription.

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Textbook Question

Draw a hypothetical metabolic pathway in Neurospora crassa composed of five substrates, five enzymes, and a product called nirvana. Number the substrates 1–5, and label the enzymes A–E, in order. (For instance, enzyme A catalyzes the reaction between substrates 1 and 2.) (b) Suppose a mutant strain can survive if substrate 5 is added to the growth medium, but it cannot grow if substrates 1, 2, 3, or 4 are added. Which enzyme in the pathway is affected in this mutant?

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Controlling the rates of transcription and translation is important in bacteria to avoid collisions between ribosomes and RNA polymerases. Calculate what the maximum rate of translation by a ribosome in a bacterial cell would have to be, in units of amino acids per second, so as not to overtake an RNA polymerase that is synthesizing mRNA at a rate of 60 nucleotides per second. How long would it take for this bacterial cell to translate an mRNA containing 1800 codons?

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