Antisense rna and dna

ANTISENSE
RNA and DNA
By: Dr. Erin A. Sharkawy

Basic Science:
-Genes contain the information necessary to
produce proteins.
-Protein production occurs in two phases
called transcription and translation.
-In the transcription phase, the DNA strand is
used as a template for manufacturing an
mRNA molecule.

-mRNA is responsible for communicating the
genetic message in the DNA to the cell so
that protein production can take place.
-In the translation phase, the mRNA travels to
the ribosome, and carry out protein synthesis.

Normally only one of the two DNA strands in
a given portion of double helix is transcribed
into RNA and always the strand for a given
gene (sense DNA ).
if a cloned gene is engineered so that the
only opposite (antisense DNA)is transcribed ,
the result will be antisense RNA with a
sequence complementary to the normal RNA
transcript.

Antisense RNA . When synthesized in large
enough amounts will often hybridize with the
sense RNA made by normal genes and
therapy inhibit the synthesis of the
corresponding protein.
Based on this conception , a versatile new
approach for shutting off an endogenous
cellular gene targets the gene’s mRNA rather
than the gene itself.

Overview:
-Currently, a total of ~4,000 genetic
disorders are known.
-The mutated genes produce proteins that
cannot function properly, leading to the
occurrence of the diseases.
-Examples: Sickle-cell anemia, Cystic fibrosis,
Color blindness

How to stop genetic disorder
using DNA drugs?
-Design a short DNA sequence that matches the
sequence of mRNA that is transcribed from the
mutated gene (which causes diseases).
-The DNA drug binds to the mRNA
-The mRNA cannot be translated to protein
-Because no disease-causing protein, disease is
cured

Antisense Technology
Antisense technology interrupts the translation
phase of the protein production process by:
1-Preventing the mRNA instructions from
reaching the ribosome.
2-Inhibiting the protein synthesis.

Antisense drugs
Antisense drugs are short, chemically
modified complementary nucleotide chains
that hybridize to a specific complementary area
of mRNA.
Antisense drugs are being researched to
treat a variety of diseases such as cancers
(including lung cancer, colorectal carcinoma,
pancreatic carcinoma , and malignant
melanoma), diabetes, muscular dystrophy and
diseases such as asthma, arthritis.

The idea is to introduce into cell an RNA or
single stranded DNA molecule that is
complementary to the mRNA of the target
gene.
*several strategies have been used to
introduce antisense nucleic acids into cells:
1- antisense RNA was synthesized into vitro
using bacteriophage RNA polymerase and
then microinjected into cells .

2- introducing antisense NA into cells using
synthetic single stranded DNA oligonucleotides.
when short nucleotides complementary to the
sequence around the transitional initiation site (the
AUG codon) of a mRNA enter cells ,they hybridize
to the mRNA and prevent the initiation of the
translation .
simply adding high conc. of such nucleotides to
cell culture is sometimes sufficient to prompt cells
to take them in or we can modify the
oligonucleotides chemically
to increase the efficiency entering the cells and
their stability inside.

* this method has been used to turn off
oncogene function .
*Antisense oligonucleotides directed against
viral RNA can protect cells against viral
infection.
*Antisense technology offers hope for new
therapies for cancer and for viral diseases ,
such as AIDS.

MECHANISM OF ANTISENSE THERAPY

-Most potential therapies have not yet
produced significant clinical results though
two antisense drugs have been approved
by the U.S. FDA :
-
-one of them is:
* Fomivirsen -marketed as Vitravene as a
treatment for cytomegalovirus retinitis.

Antisense rna and dna

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Antisense rna and dna