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Chapter 13: Problem 4

Contrast the roles of tRNA and mRNA during translation, and list all enzymes that participate in the translation processes.

Short Answer

Expert verified
Answer: In translation, mRNA serves as a template for protein synthesis, carrying genetic information from DNA to the ribosome. tRNA matches the correct amino acids to the mRNA codons, bringing them to the ribosome for protein synthesis. The enzymes involved in translation are aminoacyl-tRNA synthetase, initiation factors (IFs), elongation factors (EFs), release factors (RFs), and peptidyl transferase, which respectively attach amino acids to tRNA molecules, form the initiation complex, assist in elongation, participate in termination, and form peptide bonds during translation.

Step by step solution

01

Role of mRNA in translation

During translation, mRNA (messenger RNA) serves as a template for protein synthesis. It carries the genetic code from DNA, in the form of nucleotide sequences (codons), and provides this information to the ribosome, which assembles amino acids to form the corresponding polypeptide chain.
02

Role of tRNA in translation

To match the correct amino acids to the mRNA codons, tRNA (transfer RNA) molecules have a specific role in translation. Each tRNA has an anticodon, which is complementary to a specific codon on the mRNA molecule, allowing it to bind the corresponding amino acid. The tRNA brings its linked amino acid to the ribosome, where it will be incorporated into the growing polypeptide chain during protein synthesis.
03

Enzyme 1: Aminoacyl-tRNA synthetase

Aminoacyl-tRNA synthetase is responsible for attaching the correct amino acid to its corresponding tRNA molecule. In this process, the enzyme catalyzes the formation of an ester bond between the amino acid and the tRNA, creating an aminoacyl-tRNA complex, which is then ready to participate in translation.
04

Enzyme 2: Initiation factors (IFs)

Initiation factors (IFs) are enzymes that facilitate the formation of the initiation complex. The initiation complex consists of the small ribosomal subunit, the initiator tRNA (which carries the first amino acid, usually methionine), and the mRNA molecule. IFs help to correctly position the mRNA and the initiator tRNA on the small ribosomal subunit, allowing translation to begin.
05

Enzyme 3: Elongation factors (EFs)

Elongation factors (EFs) are enzymes that assist in the elongation step of translation. They promote the sequential binding of aminoacyl-tRNA molecules to the ribosome, translocation of the ribosome along the mRNA molecule, and formation of the peptide bonds between adjacent amino acids.
06

Enzyme 4: Release factors (RFs)

Release factors (RFs) are enzymes that participate in the termination step of translation. When the ribosome encounters a stop codon (UAA, UAG, or UGA), which has no corresponding tRNA anticodon or amino acid, an RF recognizes the stop codon and induces the hydrolysis of the bond between the tRNA and the polypeptide chain. This action releases the completed polypeptide chain, and the ribosome dissociates from the mRNA.
07

Enzyme 5: Peptidyl transferase

Peptidyl transferase is an enzyme located in the large ribosomal subunit and has a central role in forming peptide bonds during translation. This enzyme catalyzes the transfer of an amino acid from the tRNA in the ribosome's A-site to the amino acid already bound to the peptidyl-tRNA in the P-site, resulting in the formation of a peptide bond and elongation of the polypeptide chain.

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Most popular questions from this chapter

Explain why the one-gene:one-enzyme hypothesis is no longer considered to be totally accurate.

A series of mutations in the bacterium Salmonella typhimurium results in the requirement of either tryptophan or some related molecule in order for growth to occur. From the data shown here, suggest a biosynthetic pathway for tryptophan.

Francis Crick proposed the adaptor hypothesis for the function of tRNA. Why did he choose that description?

How does an enzyme function? Why are enzymes essential for living organisms?

In this chapter, we focused on the translation of mRNA into proteins as well as on protein structure and function. 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) What experimentally derived information led to Holley's proposal of the two-dimensional cloverleaf model of tRNA? (b) What experimental information verifies that certain codons in mRNA specify chain termination during translation? (c) How do we know, based on studies of Neurospora nutritional mutations, that one gene specifies one enzyme? (d) On what basis have we concluded that proteins are the end products of genetic expression?
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