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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 32a
Chapter 9, Problem 32a

A eukaryotic mRNA has the following sequence. The 5' cap is indicated in italics (CAP), and the 3' poly(A) tail is indicated by italicized adenines.
5′-CAPCCAAGCGUUACAUGUAUGGAGAGAAUGAAACUGAGGCUUGCCACGUUUGUUAAGCACCUAUGCUACCGAAAAAAAAAAAAAAAAAAAAAAAA-3′
Locate the start codon and stop codon in this sequence.

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1
Identify the start codon in the mRNA sequence. The start codon in eukaryotic mRNA is typically AUG, which codes for methionine. Scan the sequence from the 5' end to locate the first occurrence of AUG.
Determine the reading frame starting from the identified start codon (AUG). This means grouping the nucleotides into codons (triplets) starting from the AUG.
Search for the stop codon within the same reading frame. The stop codons in mRNA are UAA, UAG, and UGA. These codons signal the termination of translation.
Verify that the stop codon is downstream of the start codon and within the same reading frame. Ensure that the sequence between the start and stop codons is divisible by three, as codons are read in triplets.
Record the positions of the start codon (AUG) and the stop codon (UAA, UAG, or UGA) within the sequence. These positions will indicate the boundaries of the coding region of the mRNA.

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Key Concepts

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

mRNA Structure

mRNA, or messenger RNA, is a single-stranded molecule that carries genetic information from DNA to the ribosome for protein synthesis. It features a 5' cap that protects the RNA from degradation and aids in ribosome binding, and a 3' poly(A) tail that enhances stability and translation efficiency. Understanding the structure of mRNA is crucial for identifying functional elements like start and stop codons.
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03:49
Ribosome Structure

Start Codon

The start codon is a specific sequence of three nucleotides (AUG) that signals the beginning of translation in protein synthesis. It is recognized by the ribosome, which assembles around the mRNA to initiate the process of translating the genetic code into a polypeptide chain. Locating the start codon is essential for determining where the protein-coding sequence begins.
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Translation initiation

Stop Codon

A stop codon is a nucleotide triplet (UAA, UAG, or UGA) that signals the termination of protein synthesis. When the ribosome encounters a stop codon during translation, it releases the newly synthesized polypeptide chain, concluding the process. Identifying the stop codon is vital for understanding where the coding sequence ends and for predicting the length of the resulting protein.
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Translation Termination
Related Practice
Textbook Question

A DNA sequence encoding a five-amino acid polypeptide is given below.

...ACGGCAAGATCCCACCCTAATCAGACCGTACCATTCACCTCCT...

...TGCCGTTCTAGGGTGGGATTAGTCTGGCATGGTAAGTGGAGGA...

What is the function of the Shine–Dalgarno sequence?

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Textbook Question

A portion of the coding strand of DNA for a gene has the sequence

5′-...GGAGAGAATGAATCT...-3′

Write out the template DNA strand sequence and polarity as well as the mRNA sequence and polarity for this gene segment.

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Textbook Question

A portion of the coding strand of DNA for a gene has the sequence

5′-...GGAGAGAATGAATCT...-3′

Assuming the mRNA is in the correct reading frame, write the amino acid sequence of the polypeptide using three-letter abbreviations and, separately, the amino acid sequence using one-letter abbreviations.

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Textbook Question

A eukaryotic mRNA has the following sequence. The 5' cap is indicated in italics (CAP), and the 3' poly(A) tail is indicated by italicized adenines.

5′-CAPCCAAGCGUUACAUGUAUGGAGAGAAUGAAACUGAGGCUUGCCACGUUUGUUAAGCACCUAUGCUACCGAAAAAAAAAAAAAAAAAAAAAAAA-3′

Determine the amino acid sequence of the polypeptide produced from this mRNA. Write the sequence using the three-letter and one-letter abbreviations for amino acids.

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Textbook Question

Diagram a eukaryotic gene containing three exons and two introns, the pre-mRNA and mature mRNA transcript of the gene, and a partial polypeptide that contains the following sequences and features. Carefully align the nucleic acids, and locate each sequence or feature on the appropriate molecule.

a. The AG and GU dinucleotides corresponding to intron-exon junctions
b. The +1 nucleotide
c. The 5' UTR and the 3' UTR
d. The start codon sequence
e. A stop codon sequence
f. A codon sequence for the amino acids Gly-His-Arg at the end of exon 1 and a codon sequence for the amino acids Leu-Trp-Ala at the beginning of exon 2

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Textbook Question

Table C contains DNA-sequence information compiled by Marilyn Kozak (1987). The data consist of the percentage of A, C, G, and T at each position among the 12 nucleotides preceding the start codon in 699 genes from various vertebrate species and at the first nucleotide after the start codon. (The start codon occupies positions +1 to +3 and the first nucleotide immediately after the start codon occupies position +4) Use the data to determine the consensus sequence for the 13 nucleotides ( -12 to -1 and +4) surrounding the start codon in vertebrate genes.

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