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Chapter 12: Problem 16

Most proteins have more leucine than histidine residues but more histidine than tryptophan residues. Correlate the number of codons for these three amino acids with this information.

Short Answer

Expert verified
Answer: The number of codons for each amino acid directly correlates with their occurrence in proteins. Leucine has more codons (6) than both histidine (2) and tryptophan (1), which means leucine is more likely to be present in protein sequences. Similarly, histidine has more codons (2) than tryptophan (1), making histidine more common in proteins than tryptophan.

Step by step solution

01

Determine the Genetic Code of Leucine, Histidine, and Tryptophan

First, we need to search for the genetic code of these three amino acids. This information can be found in a genetic code table. Upon checking the table, we find that: - Leucine (Leu, L): 6 codons (UUA, UUG, CUU, CUC, CUA, CUG) - Histidine (His, H): 2 codons (CAU, CAC) - Tryptophan (Trp, W): 1 codon (UGG)
02

Compare the Number of Codons

Now that we know the number of codons for each amino acid, we can compare them: Leucine has more codons (6) than both histidine (2) and tryptophan (1). This means that there is a higher chance that leucine will be present in the protein sequence. Histidine also has more codons (2) than tryptophan (1), so histidine is expected to occur more often than tryptophan in a protein sequence.
03

Correlate the Codon Numbers with the Information Given

The information given stated that most proteins have more leucine than histidine residues and more histidine than tryptophan residues. Based on the number of codons we found for each amino acid, this holds true: Leucine (6 codons) > Histidine (2 codons) > Tryptophan (1 codon). This means that the number of codons for each of the three amino acids directly correlates with their occurrence in proteins.

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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?

A glycine residue exists at position 210 of the tryptophan synthetase enzyme of wild-type \(E .\) coli. If the codon specifying glycine is GGA, how many single-base substitutions will result in an amino acid substitution at position 210 , and what are they? How many will result if the wild-type codon is GGU?

Describe the structure of RNA polymerase in bacteria. What is the core enzyme? What is the role of the \(\sigma\) factor?

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?
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