How it all began

By By Robert Ireland

By Robert Ireland

In the world of biological research, scientists don’t care about the chicken or the egg. When they ask, “What came first,” it’s either DNA or proteins, and one U researcher said he knows the answer.

Raymond Gesteland, distinguished professor of human genetics, discussed evidence that RNA might be the original genetic material pre-dating DNA at the Frontiers of Science lecture Feb. 15 in the biology building.

Gesteland tackled the question of how DNA-based life could have evolved if the specialized proteins required for replication, which are encoded within DNA, did not yet exist.

“You have to have a protein to make DNA, and you need DNA to make a protein,” he said. “RNA helps us to understand that dilemma.”

RNA is like DNA with slight differences; it almost always occurs as a more reactive, less stable, single-stranded molecule, Gesteland said.

Scientists theorize that prior to the rise of DNA-based microbial life 3.6 billion years ago, microbial precursors might have stored genetic material in the RNA molecule, making the early earth an RNA world, Gesteland said.

When a cell produces a protein from a sequence in DNA, it first transcribes the instructions for building the protein into a messenger molecule-known as mRNA.

The mRNA molecule carries the genetic instructions to a ribosome, which uses the mRNA to produce a corresponding protein.

Initially, scientists believed that the RNA in a ribosome functioned as a scaffolding for the proteins, Gesteland said.

Gesteland pointed out that when researchers deduced the structure of a ribosome, they discovered that RNA acted as the catalyst to produce proteins.

“There are RNA molecules in cells that can catalyze reactions just like proteins,” he said.

This fact has significant implications for an RNA world, he said.

The theory that RNA was the original genetic material is supported by the combined evidence of RNA’s role as a carrier of information between DNA and protein, its catalytic activity in cells and its ability to act as a repository for the genetic material of retroviruses.

By producing proteins that could process DNA, the RNA world opened the door for the evolution of the DNA world and offers a potential solution to the problem of what came first, DNA or proteins, Gesteland said.

The more chemically reactive nature of RNA, Gesteland pointed out, suggests that evolution may have progressed rapidly in an RNA world since mutations would have occurred more frequently.

Gesteland stressed that researchers have a long way to go before the RNA-world hypothesis is strongly supported.

While researchers have found RNA molecules that catalyze the production of proteins, scientists have not found an RNA molecule capable of self-replication-a key event in the origin of life.

Jon Seger, professor of biology, agreed with Gesteland.

“The RNA world hypothesis is about a specific problem, and it is a beautiful explanation,” he said.

“(But) it’s far from being proven,” he added.

Katharine Osborn, a junior in biology, said she felt the lecture could help students “understand the process of the scientific method,” and encourage them to be “critical thinkers in pursuit of the truth.”

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