Scientists have found DNA can shape-shift and repair molecular damage, which might explain why it became the store for the genome, in spite of the RNA. In high school, many were taught that RNA was considered the essential element for life until DNA replaced it.

Interestingly, scientists did not know why this happened, until a new study published on Monday in the journal Nature Structural and Molecular Biology. The team of researchers focused on the ‘double helix’ shape of the DNA, which has a very dynamic nature. The double helix is formed by two strings and has ‘steps’ that join the two strands, being comprised of hydrogen, carbon, oxygen and nitrogen.

This specific base pair was seen very rarely since the microscope was not enough to grasp it, which led the scientific world to believe it was not an important or frequent element of the DNA. Image Credit: ACCAD
This particular base pair was seen very rarely since the microscope was not enough to grasp it, which led the scientific world to believe it was not an important or frequent element of the DNA. Image Credit: ACCAD

Hashim M. Al-Hashimi, professor of biochemistry at Duke University School of Medicine is the senior author of the study. For him, the “Hoogsteen base pair” (known this way because biochemist Karst Hoogsteen first discovered it in 1959) is the key element in understanding why the DNA triumphed over the RNA.

“There is an amazing complexity built into these simple beautiful structures, whole new layers or dimensions that we have been blinded to because we didn’t have the tools to see them, until now” claimed Al-Hashimi.

However, in 2011, Al-Hashimi and his colleagues decided to inspect the DNA molecules under a nuclear magnetic resonance (NMR) machine.

The Experiment

This idea allowed them to visualize the DNA movement at a molecular level, and finally, the elusive Hoogsteen base pair could be studied. The scientist discovered all four nucleic acid base pairs that conform the ‘steps’ connecting the helix are in a continued movement, changing their shapes between two forms.

The majority of the time they look the way James Watson and Francis Crick described more than half a century ago, the rest of the time, they form a Hoogsteen pair. For Al-Hashimi, is almost as if the molecules were ‘dancing’.

The Hoogsteen pair is created when one base rotates 180 degrees about the other, and it appears when the DNA is damaged by ‘chemical insults’. For example, when carcinogenic chemicals add a “methyl group” – one carbon atom bonded to three hydrogen atoms- to the DNA, or acted ‘upon a protein,’ as stated by Al-Hashimi.

At any point, 1 percent of all base pairs become a Hoogsteen pair, and the ‘flip’ the helix does when transforming a Hoogsteen pair is what permits the DNA to overcome these damages.

According to Al-Hashimi “DNA seems to use these Hoogsteen base pairs to add another dimension to its structure, morphing into different shapes to achieve added functionality inside the cell.”

Why DNA triumphed over RNA

Once the DNA was found to be shape-shifters, the researchers wanted to figure it out if RNA worked the same way. RNA also has a helix shape, and when the team added a methyl group to its molecules, the RNA collapsed, and the helix unraveled.

This means the RNA is incapable of forming the Hoogsteen pair, apparently because the RNS’s molecular structure is more compact and dense that the DNA’s molecular structure.

It is important to note, however, that RNA still ‘exist’, but not as the base of the genome, instead being a ‘messenger’ of the information inscribed in DNA, where it proceeds to ‘carry’ it to the protein-production center. Image Credit: Science Daily
It is important to note, however, that RNA still ‘exist’, but not as the base of the genome, instead being a ‘messenger’ of the information inscribed in DNA, where it proceeds to ‘carry’ it to the protein-production center. Image Credit: Science Daily

The scientists concluded that if our genome was made out of RNA, we could not have survived the chemical damage that frequently occurs in the genome. It is precisely the DNA’s ability to be more resilient what makes it a better repository of the genome and is what gave it the advantage to become the essential “building block” of evolution and life.

The addition of the methyl group, and the fact that the RNA fell apart, actually made the molecules more efficient in delivering information.

“It seems that nature has exploited the inability of RNA to absorb damage to create this molecular switch,” explained Al-Hashimi. By methylating the RNA you can increase production of proteins. It is amazing that we are discovering these basic properties so late in the game. We need to continue to zoom in to obtain a deeper understanding regarding these basic molecules of life.”

The Golden Age of RNA

The ribonucleic acid (better known as RNA) is a polymeric molecule; this means it is composed of many repeated subunits. The RNA was a vital part of evolution billions of years ago, when the precursors of the first ever living organism were just strands of RNA with the ability to ‘self-replicate’.

This simple element became the base of every single living organism in life, and life itself as humanity has known it. However, over the course of millions of years, the RNA was replaced by the deoxyribonucleic acid (DNA), a more sophisticated and efficient acid.

Source: IBT