OUTLINE OF REPLICATION, TRANSCRIPTION AND TRANSLATION
REPLICATION OF DNA
The first step is that the double helix is unwound by a helicase.
A molecule of a DNA polymerase binds to one strand of the DNA and begins moving
along it in the 3' to 5' direction, using it as a template for assembling a leading strand of
nucleotides and reforming a double helix. In eukaryotes, this molecule is called DNA
polymerase. Because DNA synthesis can only occur 5' to 3', a molecule of a second type
of DNA polymerase binds to the other template strand as the double helix opens. This
molecule must synthesize discontinuous segments of polynucleotides (called Okazaki
fragments). Another enzyme, DNA ligase then stitches these together into the lagging
strand.When the replication process is complete, two DNA molecules — identical to
each other and identical to the original — have been produced. Each strand of the
original molecule has remained intact as it served as the template for the synthesis of a
complementary strand.
This mode of replication is described as semi-conservative: one-half of each new
molecule of DNA is old; one-half new.
This process occurs in nucleus of the cell.
TRANSCRIPTION
A part of DNA is copied into complementary strand of RNA. This process is
catalyzed by the enzyme RNA polymerase. The difference between replication and
trancription is that RNA is a single strand. RNA in his structure has sugar ribose and has
base uracil instead thymine. Synthesis of the RNA proceeds in the 5′ → 3′ direction. As
each nucleoside triphosphate is brought in to add to the 3′ end of the growing strand, the
two terminal phosphates are removed. When the RNA polymerase encounters a
termination signal (a specific sequence of nucleotides), it and its transcript are released
from the DNA. Primary transcript is is long molecule RNA which included introns and
exons.Before this RNA molecule leaves the nucleus, a complexof RNA processing
enzymes removes all the intron sequence, in a process called splicing, hereby producing
a much shorter RNA molecule.Afterthis RNA processing step has been completed, the
RNA molecule moves to the cytoplasm as a messanger RNA molecule (mRNA), in order
to undergo translation.
TRANSLATION
The translation of mRNA into protein depends on adaptor molecules that
recognize both an amino acid and a triplet of nucleotides. These adaptors consist of a set
of small RNA molecules known as transfer RNA – tRNA. The tRNA molecule enforces
the universal genetic code logic: on one part the tRNA holds an anticodon, a sequence
of three RNA bases; on the other side, the tRNA holds the appropriate amino acid. The
process is finished when triplet called “codon stop” UAA; UGA; UAG appear on the
strand.
The aminoacids link together by polypeptyde bond and after create big structure called
protein.