Question

In detail, describe the structural and sequence elements that are common to all tRNA molecules, addressing the function of each of the elements. What forces stabilize the tRNAs' structural features?

Outline the steps of the ribosome cycle. At what stage do the ribosomal subunits bind to each other? To mRNA? What causes them to dissociate when protein synthesis is complete? Please be thorough.

Answer 1

Ques-1: In detail, describe the structural and sequence elements that are common to all tRNA molecules, addressing the function of each of the elements. What forces stabilize the tRNAs' structural features?

tRNA (transfer RNA): It has clover leaf structure & common to all tRNA structure. It has anticodon site is common to all tRNAs & useful to bind to the mRNA and to displace mRNA transcript from nuclear region onto the rRNA for protein synthesis. It is considered as an adaptor molecule mainly consist of 76 to 90 ribonucleotides in length

tRNA (transfer RNA): It has clover leaf structure & common to all tRNA structure. It has anticodon site to bind to the mRNA and to displace mRNA transcript from nuclear region onto the rRNA for protein synthesis. It is considered as an adaptor molecule mainly consist of 76 to 90 ribonucleotides in length

A clover structured t-RNA has stabilizing striucture with 5'-terminal phosphate group.

tRNA has meticulously associated with an “acceptor stem” of 7- to 9-base pair with 5'- to rinnucleotide with the 3'-terminal nucleotide

The other stabilizing force of tRNA is “CCA tail” at the 3 prime end. The teriatry structure of tRNA is with an amino acid loadeding using aminoacyl tRNA synthetases. These forces are going to keep the following arms of tRNA structure in stabilized condtion for translation process

D- arm of tRNA: it has dihydrouridine with a 4- to 6-bp stem

Wobbling site or the anticodon arm: it has a 5-bp stem with the three nucleotides (anticodon)

T –arm of tRNA: it has a pseudouridine with 4- to 5- bp stem & nitrogen bases can be modified mainly by methylation

Protein synthesis occurs in three steps namely, initiation, elongation and termination. During initiation, the mRNA, tRNA comes together at the ribosome and the translation initiates at the start codon (AUG, codes for methionine). In order to perform this process, correct charging of each tRNA molecule is crucial for the integrity of the genetic code because aminoacyl-tRNA synthetases or tRNA synthetases have meticulous role in adding correct amino acid to tRNAs in the presence of ATP. The acceptor stem of tRNA is profoundly fits into the active site of polypeptide. Therefore, tRNA and tRNA synthetase enzymes are essential in proofreading finally generates low error rate during chain elongation. If the charging of each tRNA molecule is disabled then polypeptide chain may be terminated without complete synthesis of protein for a reaction to catalyze various cellular reactions in liver, heart & kidney etc. Therefore, wobbling should not occur at the anticodons of the tRNA.

During elongation, amino acids added to the growing polypeptide chain according to the mRNA sequence. The aminoacyl tRNA molecules are picked up & charged by the elongation factors in the presence of GTP, Which enters the A site. On the ribosome, the mRNA codon bound at the A-site will be matched with appropriate anticodon of aminoacyl tRNA. This process is going to be disabled if the incorrect charging of each tRNA molecule occurred. The translational machinery plays a key role in this selection and proof reading.

Incorrect charging of each tRNA molecules is leading to" no binding of correct codon and anti codon", the new amino acid is not going to link the growing polypeptide chain in the P –site (peptidyl site) by a peptide bond

Orthogonal tRNAs - Aminoacyl-tRNA synthetase –proof reading:

Forces stabilize the tRNAs' structural features:

Orthogonal tRNAs are referred as synthetic tRNAs predominantly enable to insert non standard amino acid sequences with the help of Aminoacyl-tRNA synthetase through esterification process through ATP hydrolysis associated with amino acid and tRNA CCA acceptor stem & this is going to make them stalizing in the medium. Aminoacyl-tRNA synthetase enables proof reading activity in order to eliminate abnormal non coding codons to pair with amino acids. These tRNAs possess unusual molecular array of identifying codons further enable nonstandard sequences connected to amino acids.

Finally, it illustrated that the polypeptides with unusual amino acids at a specific desired place can be synthesized for microbiological and biotechnological purposes.