BOTANY Higher Secondary Second Year - Textbooks Online

The transfer of message present in the DNA is the initial step and the
message is transferred to mRNA. This is known as transcription. Based
on the message in the codon, the proteins are synthesized. This stage is
called translation.
Transcription
The process by which an enzyme system transfers the genetic
information of DNA into RNA strand is called transcription. It is the
process of copying of a complementary mRNA strand on a DNA strand.
It requires a template DNA, ribonucleotides, triphosphates like ATP
and GTP, metal ions Mg 2+ and Mn 2+ and RNA polymerase. The RNA
polymerase has a sigma factor, which initiates transcription. During
transcription, the DNA strands unwind and one of the strands functions
as the template for mRNA. The nucleotides of mRNA so formed are
complementary to those of DNA strand. However, in mRNA uracil replaces
thymine of DNA. The information for protein synthesis present in DNA
is now transcribed to mRNA. This process is known as transcription.
Translation
According to genetic information present in the mRNA, specific
aminoacids are assembled to form polypeptide chain. The process of
translating the nucleotide sequence of mRNA into the aminoacid sequence
of a polypeptide is called translation i.e. it means decoding the message
for protein synthesis. It involves attachment of mRNA to the 30S segment
of the ribosomes. The enzymes activate the aminoacids. Specific tRNA
picks up the activated aminoacids.
Initially, the tRNA bonds with aminoacid molecules. This reaction is
catalysed by aminoacyl tRNA synthetase. The tRNAs containing specific
aminoacids are now referred to ‘charged tRNAs’. The actual process of
translation begins, when the initiating aminoacyl tRNA binds to the
ribosome and base pairs with mRNA codon AUG. This reaction is
promoted by initiating factor. The polypeptide chain increases in length
by the linking of successive aminoacids as per the genetic code. Thereby,
elongation of polypeptide chain takes place. This reaction is promoted by
elongation factor.
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