INTRODUCTION:
Messanger
RNA (mRNA);
The gene present in DNA is transcribed into mRNA. This constitutes
about 2-5% of total RNA in the cell. They are generally degraded
quickly. Ribosomal
RNA (rRNA);
This constitutes about 80% of all RNA in the cell. 28S, 18S and 5S
are the major varieties. They are involved in the protein
biosynthesis. Transfer
RNA (tRNA).
There are about 60 different species present. They constitute about
15% of the total RNA in the cell. They are very stable. Small
RNA.
They constitute about 1-2% of total RNA in the cell. There are about
30 different varieties. They are very stable. Small Nuclear RNAs
(SnRNAs) are a subgroup of small RNA. Some important species of
SnRNAs are U1 (165 nucleotides), U2 (188 nucleotides), U3 (216), U4
(139), U5 (118), U6 (106). They are involved in mRNA splicing.
CENTRAL
DOGMA OF MOLECULAR BIOLOGY:
Here, the information available in the DNA is passed to messenger
RNA, which is then used for synthesis of a particular protein.
REPLICATION,
TRANSCRIPTION AND TRANSLATION:
DNA replication is like printing a copy of all the pages of a book.
The replication process occurs only at the time of cell division.
But transcription is taking place all the time. Only certain areas
of the DNA are copied that is to say, selected regions on the sense
strand. This is like taking a copy of particular page of the book.
So, the genetic information of DNA is transcribed or copied to the
messenger RNA (mRNA). During transcription, the message from the DNA
is copied in the language of nucleotides (4 letter language).
The
mRNA then reaches the cytoplasm where it is translated into
functional proteins. During translation, the nucleotide sequence is
translated to the language of amino acid sequence or 20 letter
language.
TEMPLATE
AND CODING STRANDS:
The template strand is transcribed to give rise to mRNA. The
template strand has the complementary sequence of mRNA. Then the
opposite strand has the same sequence as the mRNA. The DNA strand
having the same sequence of mRNA is called coding strand. As it is
complementary to the template strand, it is also called antitemplate
strand or nontemplate strand.
Messenger
RNA or mRNA:
It acts as a messenger of the information in the gene in DNA to the
protein synthesizing machinery in cytoplasm. It carries the message
to be translated to a protein. The template strand of DNA is
transcribed into a single stranded mRNA. This is accomplished by the
enzyme, DNA dependent RNA polymerase. The mRNA is a complementary
copy of the template strand of the DNA. However, thymine is not
present in RNA and instead Uracil will be incorporated.
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