Translation Initiation

Translation Initiation - Andrew Castleman Translation...

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4/4/11 Translation Initiation Translation is the process that follows transcription where mRNA is made from DNA. Translation involves matching the correct tRNAs to the codons of the mRNA so that the amino acids carried by the tRNAs can be linked to form the polypeptide that will become a functional protein. Translation is divided into four major parts. Initiation is the first step and the focus of the paper. It involves the preparation of the ribosome, mRNA and initiator tRNA for the beginning of protein synthesis. Elongation follows; the mRNA is “read” as amino acids are linked together to form the polypeptide. Termination occurs when the mRNA codes for a stop codon that does not have a complementary tRNA resulting a releasing of the polypeptide from the ribosome. Finally, the ribosome is recycled as the ribosomal subunits dissociate releasing the mRNA. The initiation of translation is very important for bacteria. The initiation of translation is the process which is controlled by the bacteria to control the amount of protein made. The assembly of the initiation complex takes seconds and varies for each mRNA. The initiation complex is formed by the 50S subunit and 30S subunit of the ribosome holding the initiator tRNA and mRNA and is assembled by three proteins, initiation factors. Ribosome Overview The machinery of the translation is the ribosome. The ribosome is composed of two subunits with sedimentary rates of 50 and 30S that combine to form a 70S ribosome. The ribosome consists mainly of rRNA and approximately one third of its weight is protein. The ribosome is held together by three types of stabilizing interactions. Mg 2+ bridges form between the negative charges of the phosphates that make RNA a polyanion. RNA interacts with other RNA forming complementary base pairs and A-minor motifs which occur when an adenine inserts its minor groove into the minor groove of a helix and forms H-bonds. The backbone of the RNA of the ribosome also interacts with proteins that are able to recognize the shape of the RNA. Small Ribosomal Subunit The smaller of the ribosomal subunits consists of 21 proteins and an RNA of ~1500 nucleotides. The shape of the subunits is determined by the RNA that forms the larger part of it. The subunit’s upper third is called the head which is connected to the body by the neck. Park of the body sticks out and is called the toe. The side that faces the larger subunit is referred to as the front, while the side that is exposed to the solvent is referred to as the back. The smaller subunit is responsible for binding the mRNA via RNA-RNA base pairing interactions with the Shine-Dalgarno sequence of the mRNA. The Shine-Dalgarno sequence is also used to position the initiator tRNA on the correct codon of the mRNA. The small subunit also holds the anticodon loop and stem of the tRNAs and is responsible for ensuring the correct tRNA is linked to the mRNA. It ensures this by moving residues of its RNA to stabilize the correct base pairing of the condon and anti-codon. Large Ribosomal Subunit
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This note was uploaded on 04/22/2011 for the course BIOCHEM 412 taught by Professor Thomas during the Spring '11 term at Tennessee Martin.

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Translation Initiation - Andrew Castleman Translation...

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