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Chapter 12: Problem 4

The mRNA formed from the repeating tetranucleotide UUAC incorporates only three amino acids, but the use of UAUC incorporates four amino acids. Why?

Short Answer

Expert verified
Answer: The UUAC sequence incorporates two unique amino acids (Leucine and Tyrosine), while the UAUC sequence incorporates three unique amino acids (Tyrosine, Isoleucine, and Serine). The difference in the number of amino acids incorporated is due to the extra codon (UCU) present in the UAUC sequence, which adds an additional amino acid (Serine) to the mix.

Step by step solution

01

Break the sequence into triplet codons

In this step, we will break down the given mRNA sequences into codons. Recall that codons consist of three nucleotides each. So, let's break the tetranucleotide UUAC and UAUC into codons: For UUAC, the possible codons are UUA and UAC, and for UAUC, the possible codons are UA, UCU, and AUC.
02

Use the genetic code table to find corresponding amino acids

Now that we have the codons for each sequence, we can use the genetic code table to determine which amino acids are incorporated by each sequence. Below are the corresponding amino acids for each codon: UUAC: - UUA: Leucine (Leu) - UAC: Tyrosine (Tyr) UAUC: - UAU: Tyrosine (Tyr) - AUC: Isoleucine (Ile) - UCU: Serine (Ser)
03

Count the amino acids incorporated in each sequence

Now that we have determined the amino acids for the codons in each sequence, we can count the number of unique amino acids incorporated by each sequence: - UUAC: Leucine and Tyrosine (2 unique amino acids) - UAUC: Tyrosine, Isoleucine, and Serine (3 unique amino acids)
04

Analyze the difference

With all the unique amino acids incorporated by each sequence counted, we can see that the UUAC sequence incorporates only two amino acids, not three as mentioned in the question. The UAUC sequence incorporates three amino acids as mentioned. The difference between the two sequences is due to the fact that the UAUC sequence has one additional codon (UCU) compared to the UUAC sequence, which adds an extra amino acid into the mix (Serine). The question seems to have a small error, as the UUAC sequence incorporates only two amino acids, not three.

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Most popular questions from this chapter

Messenger RNA molecules are very difficult to isolate from bacteria because they are quickly degraded. Can you suggest a reason why this occurs? Eukaryotic mRNAs are more stable and exist longer in the cell than do bacteria mRNAs. Is this an advantage or a disadvantage for a pancreatic cell making large quantities of insulin?

In this chapter, we focused on the genetic code and the transcription of genetic information stored in DNA into complementary RNA molecules. Along the way, we found many opportunities to consider the methods and reasoning by which much of this information was acquired. From the explanations given in the chapter, what answers would you propose to the following fundamental questions: (a) How did we determine the compositions of codons encoding specific amino acids? (b) How were the specific sequences of triplet codes determined experimentally? (c) How were the experimentally derived triplet codon assignments verified in studies using bacteriophage MS2? (d) How do we know that mRNA exists and serves as an intermediate between information encoded in DNA and its concomitant gene product? (e) How do we know that the initial transcript of a eukaryotic gene contains noncoding sequences that must be removed before accurate translation into proteins can occur?

Alternative splicing is a common mechanism for eukaryotes to expand their repertoire of gene functions. At least one estimate indicates that approximately 50 percent of human genes use alternative splicing, and approximately 15 percent of diseasecausing mutations involve aberrant alternative splicing. Different tissues show remarkably different frequencies of alternative splicing, with the brain accounting for approximately 18 percent of such events. (a) Define alternative splicing and speculate on the evolutionary strategy alternative splicing offers to organisms. (b) Why might some tissues engage in more alternative splicing than others?

In studies of the amino acid sequence of wild-type and mutant forms of tryptophan synthetase in \(E .\) coli, the following changes have been observed: Determine a set of triplet codes in which only a single-nucleotide change produces each amino acid change.

Define the process of transcription. Where does this process fit into the central dogma of molecular genetics?
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