Translation

TRANSLATION

 Translation is the process which mRNA is decoded and translate to produce a polypeptide sequence (protein ).Translation occur at ribosome. The genetic code is important in translate the mRNA to polypeptide . 

The genetic code has three important characteristics :

• The code is degenerate. One codon only can code one amino acid .
• It is non-overlapping. Each base is only part of one codon, and each codon codes for one amino acid.
• It is almost universal. The same sequences of bases code for the same amino acid in all organism.

What is Codon ?

Codon is genetic code that is read in three-letter grouping called codons. A codon is group of three nucleotide bases in messenger RNA that specifies a particular amino acid.

 

There are 64 types of codon that can be found in translation. 

61 codon are code for amino acid, 1 codon (AUG) is code for initiation signal and 3 codon (UAA, UAG, and UGA ) are for termination signal.

WHAT IS tRNA?

•   tRNA or transfer RNA is a type of RNA found in cells. 
• It is single stranded and 10–15% of the total RNA. tRNA is synthesised in the nucleus by the DNA. 
• It is also known as Adapter RNA. The major function of the tRNA is to carry amino acids at the time of Protien synthesis (Translation). tRNA is clover leaf-like in structure and has foldings.Due to the folding, some complementary nitrogenous bases come across each other and form hydrogen bonds. There are some places where the Hydrogen bonds are not formed, these places are known as loops.

STAGE OF TRANSLATION

There are three stage of translation that are needed for complete the translation process.

1. Initiation 

•     The initiation stage of translation brings together with mRNA, tRNA with the first amino acid, and two ribosomal subunits. 
•  Firstly, a small ribosomal subunits binds with mRNA and a special initiator tRNA.
• Then, the small subunits move along the mRNA until it reaches the start codon (AUG).
• Protein called initiator factors bring in the large subunits that completes the translation initiator complex.

     2.  Elongation

• In elongation, is simply the ribosome travelling down the message, reading codons and bringing in the proper aminoacyl tRNA's to translate the message out to protein. 
• The incoming aminoacyl tRNA is brought into the ribosome A site, where it is matches with the codon being presented. 
• once it has been secured ( by hydrolisis ) codon being presented.
•  Once it has been secured ( by hydrolysis of GTP to "fix" it in place ) , the peptidyl transferase reaction occurs.
•  This is where the bond between peptide and theaminoacyl tNA in the P site is broken, while a new bond is simultaneously formed between the new amino acid in the A site. 
• The ribosome then moves over by 3 bases, the spent tRNA is rejected from E site.

    

  3. Termination

• Termination of translation occurs when the ribosome encounters a stop codon. 
• There are slightly different views as to what happens.
• There is release factor bound to the stop codon, that displaces the ribosome when it reaches the point.
• The stop codon is simply a codon that has no matching tRNA, so the ribosome stalls, waiting for the next aminoacyl tRNA.
• This stall causes the ribosome destabilize, and release the factors come in to disassemble the ribosome and cut free the peptide strand.