Question

In a eukaryotic cell, if DNA is stored in the nucleus and protein synthesis occurs in the cytoplasm, then how does the information in DNA become functional (i.e. processed into protein)?

Answer 1

Answer In a eukaryotic cell, the DNA is stored in the nucleus and protein synthesis occurs in the cytoplasm. Still the information in DNA become functional via 2 sequential processes :

1. Transcription in the nucleus

2. Translation in the cytoplasm

Transcription means that the information in the DNA is copied into RNA. Enzyme used is RNA Polymerase and mRNA is formed from DNA in this process.

DNA templates have genetic information coded in the form of Anti-triplet codons (3 Nitrogenous bases in a row). When mRNA is transcribed we get Triplet Codons (on mRNA) specific to each Anti- triplet codons of DNA on basis of following principles:

Bases in DNA Bases in m-RNA

   T    A

  A U

G    C

C    G

Here A is Adenine, T is Thymine, G is guanine and C is Cytosine.

Newly synthesised (or transcribed) mRNA comes out of nucleus of eukaryotic cell and begins the process of translation on ribosomes.

Translation : in this process mRNA attaches on Ribosomes in the cytoplasm of the cell and forms a polypeptide chain on the basis of codons found on mRNA. Each codon results into an Amino Acid and hence a chain of amino acids linked by peptide bond is formed which is called as polypeptide chain.

e.g AAG Codon leads to formation of Lysine amino acid, AUG for Methionine etc.

But, This is primary structure of protein. When this polypeptide chain folds and forms secondary and tertiary structures due to hydrogen bonds, disulphides bonds etc., the protein becomes active protein.

so we find the protein has information coming from mRNA which had information coming from DNA hence we can say that information in the DNA becomes functional (i.e processed into protein)