Biosynthesis of protein.

Date: 2015-10-07; view: 628.

Biosynthesis of protein is a process of forming a protein according to information (instruction) of DNA and mRNA.

The steps of biosynthesis of protein are:

- Transcription

- Recognition

- Translation

- Modification

Transcriptionis the synthesis of mRNA.

First of all DNA double helix uncoil and splints into two chains. This is brought about by the enzyme RNA-polymerathe. The enzyme causes the formation of rRNA that growth in length as the enzyme moves along the DNA. Only one strand of DNA is the master strand (sense strand) and functions as a template. The forming mRNA chain contains nitrogen bases that are complementary to bases of DNA.

There are some differences exist between prokaryotic and eukaryotic translation. Prokaryotic mRNA is used immediately after transcription, but eukaryotic mRNA undergo specific posttranscriptional modification and processing.

The posttranscriptional modification and processing are the final steps of mRNA synthesis. A lot of eukaryotic genes have intervening sequences – introns. These sequences don't contain information of the amino acids of protein, apposed to exons (expressed sequences), whit are parts of the protein-coding sequence.

As a result of transcription of gene containing introns a large RNA transcript is copied. It named as precursor mRNA or pre-mRNA. The molecule contains both exons and introns. Then the introns have to be removed and the exons have to be spliced together to form a continuous protein-coding message.

Finally processes of capping and tailing occur and mRNA is formed.

Recognition is a process of specific binding of determined amino acid by tRNA and transfer the amino acid to ribosome, where the synthesis of protein occurs.

The amino acid-AMP-enzyme complex joins to the amino acid-binding site of its specific tRNA of its specific tRNA. The aminoacyl-tRNA synthetase enzyme catalyzes the reaction. As a result the complex that is called a charged tRNA is formed. The process is named as charging of tRNA. Thecharged tRNAmoves to ribosome.

Translation is a process of collection of protein on the base of mRNA instruction according the genetic code in a ribosome.

First of all activation of ribosomes occurs. This is brought by mRNA molecule. Then initiation, elongation, and termination go on.

Initiation occurs due to presence of “initiator” or “start” codon (AUG) at the 5' end of mRNA. The codon signals the start of polypeptide formation. The tRNA whit having anticodon UCA brings methionine. Methionine is a first amino acid of any polypeptide that is forming. If it is necessary this amino acid is separated later.

Elongationis processof joining the second, the third and following amino acids to forming polipeptide chain. The elongation includes of a temporary join a charged tRNA to complementary codon of mRNA within the special site of ribosome. And then the amino acid, binded with tRNA attach to newly forming polipiptide chain.

Terminationis a process of completion of polipeptide synthesis. It realize due to presence at the end of each mRNA a “stop” or “terminator” codon (UAA,UAG or UGA). It is not joined by the anticodon of any tRNA-amino acid complex, it is joined by the terminate factor and synthesis of polipeptide is completed.

Modification is process of forming the secondary, the tertiary, and, sometimes, the quaternary structure of protein. The just released polipeptide has primary structure. It is straight linear molecule. Polipeptide may lose amino acids from the end and coil (secondary structure) or fold (tertiary structure) itself. The combination of two or more peptides is quaternary structure.