Question

1. Discuss the molecular mechanisms of tRNA and how it relates to the genetic code? (500 words)

Answer 1

To manufacture protein molecules, a cell must first transfer information from DNA to mRNA through the process of transcription. Then, a process called translation uses this mRNA as a template for protein assembly.  Ribosomes are the specialized cellular structures in which translation takes place.ribosomes are the sites at which the genetic code is actually read by a cell. Ribosomes are themselves composed of a complex of proteins and specialized RNA molecules called ribosomal RNA (rRNA). During translation, ribosomes move along an mRNA strand, and with the help of proteins called initiation factors, elongation factors, and release factors, they assemble the sequence of amino acids indicated by the mRNA, thereby forming a protein. In order for this assembly to occur, however, the ribosomes must be surrounded by small but critical molecules called transfer RNA (tRNA).

Transfer RNAs (tRNA) are relatively small molecules, containing 70–90 nucleotides that play a special role in protein synthesis. Transfer ribonucleic acid (tRNA) is a type of RNA molecule that helps decode a messenger RNA (mRNA) sequence into a protein. The tRNA molecule has a distinctive folded structure with three hairpin loops that form the shape of a three-leafed clover. One of these hairpin loops contains a sequence called the anticodon, which can recognize and decode an mRNA codon.Each tRNA has its corresponding amino acid attached to its end.

Translation process can also be broken into three distinct phases: initiation, elongation, and termination. At the start of the initiation phase of translation, the ribosome attaches to the mRNA strand and finds the beginning of the genetic message called the start codon (AUG for methionine). Next, the specific tRNA molecule that carries anticodon( for methionine) recognizes this codon and binds to it. At this point, the initiation phase of translation is complete. The next step elongation, begins when the ribosome shifts to the next codon on the mRNA. At this point, the corresponding tRNA binds to this codon and, for a short time, there are two tRNA molecules on the mRNA strand. The amino acids carried by these tRNA molecules are then bound together. After this binding has occurred, the ribosome shifts again, and the first tRNA, which is no longer connected to its corresponding amino acid, is released. Within the ribosome, multiple tRNA molecules bind to the mRNA strand in the appropriate sequence.Each successive tRNA leaves behind an amino acid that links in sequence. The resulting chain of amino acids emerges from the top of the ribosome.The polypeptide elongates as the process of tRNA docking and amino acid attachment is repeated. In the termination phase, translation process terminates after a stop codon signals the ribosome to fall off the RNA. Thus by the combined effort of ribosomes and tRNA,  decoding of  the mRNA molecule takes place until the entire sequence is translated into a protein.