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Chapter 12: Problem 7

"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.

Short Answer

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Question: Briefly describe the steps involved in breaking the genetic code. Answer: Breaking the genetic code consists of understanding the genetic code's components, such as nucleotides, codons, and proteins. Then, the roles of messenger RNA (mRNA) and transfer RNA (tRNA) in protein synthesis are identified. Scientists deciphered the code using synthetic mRNAs and in vitro translation to determine the codons for each amino acid. Finally, a "Universal" Genetic Code Table was developed to show the relationship between nucleotide sequence and amino acid sequence.

Step by step solution

01

Understand the Genetic Code

The genetic code is the set of rules by which information encoded in DNA and RNA sequences is translated into proteins in living cells. It defines how the nucleotide sequence of the genetic material (DNA or RNA) is translated into the amino acid sequence that forms proteins.
02

Identify the Genetic Code's Components

The genetic code consists of three key components: (1) nucleotides, which are the building blocks of DNA and RNA and come in four types (adenine, guanine, cytosine, and thymine or uracil); (2) codons, which are groups of three nucleotides that specify an amino acid or serve as a stop signal; and (3) proteins, which consist of chains of amino acids called polypeptides that are responsible for various functions in living organisms.
03

Determine the Role of Messenger RNA (mRNA)

Messenger RNA (mRNA) plays an essential role in the translation of genetic information into proteins. The DNA sequence is transcribed into mRNA, which is then transferred from the nucleus to the cytoplasm of the cell. Here, the mRNA acts as a template for assembling the corresponding protein.
04

Understand the Role of Transfer RNA (tRNA)

Transfer RNA (tRNA) molecules serve as the link between mRNA and amino acids during the process of protein synthesis. Each tRNA molecule carries a specific amino acid and recognizes a complementary codon in the mRNA. This ensures that the appropriate amino acid is added to the growing polypeptide chain as dictated by the mRNA sequence.
05

Decrypting the Genetic Code Using Synthetic mRNAs and In Vitro Translation

Scientists deciphered the genetic code by using chemically synthesized mRNAs of known sequences and studying the amino acid sequences of the proteins synthesized in vitro. Through various experiments, researchers were able to determine the specific codons that correspond to individual amino acids, as well as the stop codons that signal the end of a protein.
06

Develop the "Universal" Genetic Code Table

Once the correspondence between the codons and amino acids was determined, scientists were able to compile a table that shows the relationship between the nucleotide sequence and the amino acid sequence. This table, known as the "Universal" Genetic Code Table, is a vital tool for understanding how genetic information is translated into proteins in living organisms.

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Most popular questions from this chapter

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?

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

In a mixed copolymer experiment, messages were created with either \(4 / 5 \mathrm{C}: 1 / 5 \mathrm{A}\) or \(4 / 5 \mathrm{A}: 1 / 5 \mathrm{C}\). These messages yielded proteins with the amino acid compositions shown in the following table. Using these data, predict the most specific coding composition for each amino acid. $$\begin{array}{lccc} {}{} {4 / 5 \mathrm{C}: 1 / 5 \mathrm{A}} & {}{} {4 / 5 \mathrm{A}: 1 / 5 \mathrm{C}} \\ \text { Proline } & 63.0 \% & \text { Proline } & 3.5 \% \\ \text { Histidine } & 13.0 \% & \text { Histidine } & 3.0 \% \\ \text { Threonine } & 16.0 \% & \text { Threonine } & 16.6 \% \\ \text { Glutamine } & 3.0 \% & \text { Glutamine } & 13.0 \% \\ \text { Asparagine } & 3.0 \% & \text { Asparagine } & 13.0 \% \\ \text { Lysine } & \underline{0.5 \%} & \text { Lysine } & \underline{50.0 \%} \\\ & 98.5 \% & & 99.1 \% \end{array}$$

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?

An alanine residue exists at position 180 of a certain plant protein. If the codon specifying alanine is GCU, how many singlebase substitutions will result in an amino acid substitution at position \(180,\) and what are they?
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