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Chapter 13: Problem 18

What was the initial evidence for the existence of mRNA?

Short Answer

Expert verified
Answer: The key experiments that provided initial evidence for the existence of mRNA as an intermediary molecule between DNA and proteins were conducted by Sidney Brenner, François Jacob, and Matthew Meselson in 1961 and by Elliot Volkin and Lazarus Astrachan in 1956. Brenner, Jacob, and Meselson's work involved using bacteriophages to observe the role of RNA in protein synthesis, while Volkin and Astrachan's work focused on the discovery of a new, short-lived form of RNA associated with infected bacterial cells.

Step by step solution

01

Understanding the central dogma of molecular biology

The central dogma of molecular biology, proposed by Crick in 1958, states that genetic information flows from DNA to RNA and then to proteins. According to this theory, genes (made up of DNA) are transcribed into RNA, and this RNA is then translated into proteins, which carry out various functions in the cell. The hypothesis of an intermediary molecule between DNA and proteins led to the search for messenger RNA (mRNA).
02

Discussing the key experiments

The initial evidence for the existence of mRNA came from various experiments conducted during the 1950s and 1960s. Here we'll focus on two important ones: the experiments by Brenner, Jacob, and Meselson (1961), and the experiments by Volkin and Astrachan (1956).
03

Looking at the work of Brenner, Jacob, and Meselson

Sidney Brenner, François Jacob, and Matthew Meselson conducted experiments in 1961 in which they used bacteriophages (viruses that infect bacteria) to observe the role of RNA in protein synthesis. They found that after the initial phase of infection (called the "eclipse phase"), during which no new phage particles could be found, the phage genetic material (DNA) was used to create new phage-specific RNA that was then translated into viral proteins. The newly synthesized RNA only carried the genetic information of the phage, which indicated that it serves as a template for protein production. This was the first direct evidence of mRNA as the intermediary between DNA and proteins.
04

Discussing the work of Volkin and Astrachan

Elliot Volkin and Lazarus Astrachan in 1956 discovered a previously unknown form of RNA that was specifically associated with infected bacterial cells. They found that this new RNA was rapidly synthesized and then degraded during bacteriophage infection. This led them to hypothesize that this RNA could be a short-lived intermediary molecule carrying genetic information from DNA to proteins, which we now know as messenger RNA (mRNA).
05

Concluding the initial evidence for the existence of mRNA

Through the work of scientists like Brenner, Jacob, Meselson, Volkin, and Astrachan, the concept of mRNA as a transient carrier of genetic information between DNA and proteins was developed. These groundbreaking experiments provided the foundation for our current understanding of the central dogma of molecular biology and the crucial role that mRNA plays in the flow of genetic information.

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Most popular questions from this chapter

M. Klemke et al. (2001) discovered an interesting coding phenomenon in which an exon within a neurologic hormone receptor gene in mammals appears to produce two different protein entities (XL \(\alpha\) s, ALEX). Following is the DNA sequence of the exon's \(5^{\prime}\) end derived from a rat. The lowercase letters represent the initial coding portion for the XL \(\alpha\)s protein, and the uppercase letters indicate the portion where the ALEX entity is initiated. (For simplicity, and to correspond with the RNA coding dictionary, it is customary to represent the noncoding, nontemplate strand of the DNA segment.) \(5^{\prime}-\) gtcccaaccatgcccaccgatcttccgcctgcttctgaagATGCGGGCCCAG (a) Convert the noncoding DNA sequence to the coding RNA sequence. (b) Locate the initiator codon within the XL \(\alpha\) segment. (c) Locate the initiator codon within the ALEX segment. Are the two initiator codons in frame? (d) Provide the amino acid sequence for each coding sequence. In the region of overlap, are the two amino acid sequences the same? (e) Are there any evolutionary advantages to having the same DNA sequence code for two protein products? Are there any disadvantages?

A glycine residue is in 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 \(210 ?\) What are they? How many will result if the wild-type codon is GGU?

Recent observations indicate that alternative splicing is a common way for eukaryotes to expand their repertoire of gene functions. Studies indicate that approximately 50 percent of human genes exhibit alternative splicing and approximately 15 percent of disease-causing 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 (Xu et al., 2002 . Nuc. Acids Res. \(30: 3754-3766\) ). (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?

Present an overview of various forms of posttranscriptional processing in eukaryotes. For each, provide an example.

Substitution RNA editing is known to involve either C-to-U or A-to-I conversions. What common chemical event accounts for each?
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