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Chapter 12: Problem 20

Sydney Brenner argued that the code was nonoverlapping because he considered that coding restrictions would occur if it were overlapping. A second major argument against an overlapping code involved the effect of a single nucleotide change. In an overlapping code, how many adjacent amino acids would be affected by a point mutation? In a nonoverlapping code, how many amino acid(s) would be affected?

Short Answer

Expert verified
Answer: In overlapping genetic codes, a point mutation potentially affects two adjacent amino acids. In nonoverlapping genetic codes, a point mutation affects only one amino acid.

Step by step solution

01

Define overlapping and nonoverlapping codes

In a genetic code, the codons are sequences of three nucleotides. The difference between overlapping and non-overlapping codes lies in how contiguous codons are organized in the gene. - In an overlapping code, a single nucleotide can be a part of two or more codons. - In a nonoverlapping code, each nucleotide belongs to only one codon, and codons are read consecutively, without overlap.
02

Determine the effect of a point mutation on overlapping code

In an overlapping code, a single nucleotide change in any of the codons will impact both the codon where the mutation occurred, as well as any adjacent codons that share the mutated nucleotide. Thus, if we have the sequence "ABCDEF" where letters represent nucleotides, a mutation in nucleotide "C" would affect both the ABC and CDE codons. Since a single codon corresponds to one amino acid, this means that a point mutation in an overlapping code will potentially affect two adjacent amino acids.
03

Determine the effect of a point mutation on nonoverlapping code

In a nonoverlapping code, each nucleotide is only a part of a single codon. Therefore, a point mutation will only affect the single codon where the mutation took place. As a result, only one amino acid would be impacted by this mutation.
04

Answering the questions

In an overlapping code, a point mutation will potentially affect two adjacent amino acids due to nucleotide(s) being shared by adjacent codons. In a nonoverlapping code, a point mutation will affect only one amino acid, as each nucleotide belongs to only one codon.

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Most popular questions from this chapter

In studies of frameshift mutations, Crick, Barnett, Brenner, and Watts-Tobin found that either three nucleotide insertions or deletions restored the correct reading frame. (a) Assuming the code is a triplet, what effect would the addition or loss of six nucleotides have on the reading frame? (b) If the code were a sextuplet (consisting of six nucleotides), would the reading frame be restored by the addition or loss of three, six, or nine nucleotides?

Review the Chapter Concepts list on p. 231. These all center on how genetic information is stored in DNA and transferred to RNA prior to translation into proteins. Write a short essay that summarizes the key properties of the genetic code and the process by which RNA is transcribed on a DNA.

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?

"Breaking the genetic code" has been referred to as one of the most significant scientific achievements in modern times. Describe (in outline or brief statement form) the procedures used to break the code.

A novel protein discovered in a certain plant has many leucinerich regions, fewer alanine-rich regions, and even fewer tyrosine residues. Correlate the number of codons for these three amino acids with this information.
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