Scientist Roger Hanson
SIMON O’CONNOR/STUFF
Scientist Roger Hanson

In 1953, James Watson and Francis Crick discovered that the double-stranded molecule of deoxyribose nucleic acid (DNA) was a double helix.

Another nucleic acid is called ribonucleic acid (RNA), it is a simpler, single-stranded cousin to DNA.

The key building blocks of all organisms are called proteins and the necessary processes of replication and repair to keep organisms alive require new proteins to be constructed.

An illustration of DNA helix.
An illustration of DNA helix.

This starts by copying, more accurately, “transcribing”, the correct segment of DNA into an RNA molecule using an enzyme called RNA polymerase.

The required protein is assembled by the machinery of the cell which builds up the specific sequence of molecules in a protein by “translating” the sequence of molecules present in this RNA molecule.

Francis Crick described this flow of information from DNA molecule to RNA molecule to protein as the central dogma of molecular biology.

“Dogma” is a set of principles declared to be incontrovertibly true – it derives from the Latin meaning “philosophical tenet”.

The dogma of DNA-to-RNA-to-protein was upset when in 1970 Howard Temin and independently, David Baltimore, discovered an enzyme called reverse transcriptase.

They found that in the cancer producing virus, Rous Sarcoma Virus (RSV), the flow of information is not DNA-to-RNA but RNA-to-DNA (and then to protein), the reverse of the direction proposed by Crick. For this reason, RSV is called a retrovirus.

Viruses cannot replicate on their own but have to infect the living cells of other organisms.

After infection, they hijack their host’s molecular machinery to make copies of themselves.

These copies of the virus then burst out of the cell and proceed to infect other cells. In most viruses the central dogma is followed, DNA is transcribed into RNA which is then translated into proteins.

But, most retroviruses don’t have DNA – their genetic material is contained in RNA.

When they enter the host’s cell they make the reverse transcriptase enzyme which then gets to work by transcribing itself into the host’s DNA – the information flow here is RNA to DNA.

Thereafter the host treats the new DNA as part of its own and replicates the virus genetic material.

Another aspect of the central dogma which proved wrong was that not all DNA, as Crick inferred, is involved in assembling proteins. Today, it is thought that about 2 per cent of DNA actually codes for proteins, the rest is often referred to as “junk DNA”.

Interest in retroviruses took off after 1981 when it was found that some people were becoming very ill because something was dramatically decreasing the number of their white blood cells.

White blood cells are an essential component in the immune system. The condition was called Auto Immune Deficiency Syndrome or AIDS.

The race was on to find a cure and it wasn’t long before two frontrunners emerged, Robert Gallo of the National Cancer Institute in the United States and Luc Montagnier at the Pasteur Institute in France.

In 1976, Gallo made the first discovery of a retrovirus in humans, the Human T-lymphotropic virus (HVLV). In 1983, Gallo announced in the prestigious journal Science, that he had isolated a similar virus, HTLV-III, which he said caused AIDS.

Meanwhile in Paris, Montagnier was asked to examine samples taken from the lymph nodes of AIDS patients.

He isolated a virus he called lymphadenopathy-associated virus (LAV), although he couldn’t specifically say that it caused AIDS.

His results were published in the same edition of Science as Robert Gallo’s findings.

The similarity between the two viruses was striking and after rigorous investigation it was decided that the two viruses were the same, or at least, closely related.

The investigation team decided that Luc Montagnier had been the first to make the discovery of the AIDS-causing retrovirus – now called HIV or Human Immunodeficiency Virus.

The 2008 Nobel Prize in Physiology and Medicine was awarded to Montagnier and his colleague Francoise Barre-Sinoussi. Controversially, Robert Gallo was not included.

Victims of the HIV virus have a life expectancy of between 6 to 19 months if no treatment is available.

Thanks to the efforts of scientists such as Robert Gallo, Luc Montagnier and Francoise Barre-Sinoussi, a young person with HIV, if treated early can expect to live for several decades.

 

Source: https://www.stuff.co.nz/taranaki-daily-news/news/112566563/the-central-dogma–dna-retroviruses-and-the-treatment-for-aids