Question

fully describe the process of protein synthesis beginning at DNA

Answer 1

Protein synthesis is one of the most important functions of the cell. It is carried meticulously by a set of RNAs which are called the 'protein factory' of the cell.

Messenger RNA[ mRNA] carry the coding sequence for protein synthesis from the DNA. They are called the transcripts.

Ribosomal RNA [ rRNA] form the core of a cell's ribosome .

Transfer RNA [ tRNA] molecules carry amino acids to the ribosome during protein synthesis. Now, lets discuss this step by step --

* Translation is the process of synthesis of protein from mRNA with the help of ribosomes .

There are three stages of protein synthesis :

i] INITIATION

  * Assembly of ribosomes on mRNA

* Activation of amino acids and its delivery to tRNA.

ii] ELONGATION

* Repeated cycle of amino acid delivery .

* Peptide bond formation and movement along the mRNA called translocation.

iii] TERMINATION

* The release of polypeptide chain.

Before we proceed forther, we should some facts about tRNA--

* each tRNA has five arms or loops

a] anticodon loop, which has base complementary to the code

b] amino acid receptor end to which the amino acid binds

c] T loop which helps in binding to ribosome

d] D loop which helps in binding aminoacyl synthetase

e] a variable loop

* Each tRNA is specific for a particular amino acid

* A specific tRNA for initiation is called initiator tRNA.

* There is no tRNA for stop codon

Now , let us discuss the entire process---

* The mRNA carry the genetic information from the DNA template in the form of a series of three base codes, each of which specifies a particular amino acid and move into the cytoplasm.

* The mRNAs deciphers the the code words in mRNA . Each type of amino acid has its own tRNA, which binds it and takes it to the growing end of the polypeptide chain. The correct tRNA with its attached is selected at each step because each tRNA molecule contains a three base sequence that can pair only with its complementary code on the mRNA.

* Ribosomal RNA[ rRNA] associates with a set of proteins ribosomes.

* These complex structures which physically move along an mRNA molecule, catalyse the assembly of amino acids into protein chains. They also bind tRNA and various accessory molecules necessary for protein synthesis. Ribosomes are composed of large and small sub-units, each of which contains its own rRNA molecule or molecules.

* Next is the translation by which the base sequence of an mRNA is used to order and join the amino acids into a protein molecule. Thus , the required protein is synthesised.

The three types of RNAs , namely, mRNA , tRNA and rRNA participate in this essential protein synthesising pathway in all cells ,which is the very basis of all life forms on the earth..