TSRC’s Town Talks: Scents and Knots, Molecules We Overlook

20 Jul TSRC’s Town Talks: Scents and Knots, Molecules We Overlook

What triggers our sense of smell?, image by Source/Corbis

We take for granted many things rooted in science: leaves falling, runny noses in the cold, static electricity, the scent of roasting coffee, traffic patterns. Each of these phenomena carries biological, chemical, or mathematical significance, yet they are so commonplace that rarely does anyone stop to ask, “Why or how does this happen?”

Tuesday, June 23, 6 p.m. at the historic Sheridan Opera House, TSRC Town Talks presents “Smell: What Triggers It?” and “Knots: Knitting together Mountain Climbing, Chemistry, and the Living Cell.” For both of these topics, understanding the way molecules behave, whether it’s their shape, vibrations, or spontaneous knotting, is critical to answering the scientific “whys” we so frequently overlook.

David Leitner, Professor of Theoretical and Biophysical Chemistry at University of Nevada, Reno, will explore smell.

“Remarkable progress has been made in unraveling the detailed mechanism of vision, but our understanding of how we sense molecules, our sense of smell, is not well developed,” he said.

Dimitrii Makarov, Associate Professor of Chemistry at the University of Texas at Austin, looks at knots – and not just the tying-up-rope kind.

“Usually proteins aren’t knotted, but for those that are, we don’t completely understands their significance,” he said.

Many of the molecules we smell are similar in shape and size, leading one to believe that their scents are alike. Not true, according to Leitner. Molecules that look identical can smell completely different. What’s more, humans can distinguish among a range of odorants (molecules that bind the nose’s olfactory receptors) even when only traces are floating in the air.

“Humans have hundreds of different odorant receptors lining their nasal passages, but we don’t know exactly how an odorant binds to a particular receptor. The property of the odorants that triggers our sense of smell remains a mystery. Because shape alone cannot explain how olfactory receptors differentiate among molecules, scientists have been using quantum chemistry. We describe molecules by their structure, but molecules are actually constantly in motion,” said Leitner.

In his talk, Leitner will reveal evidence that smell involves not only an odorant’s shape and size, but also its vibrational frequencies. Flies for example have been shown to discriminate between molecules of the same shape and size, but with slightly different masses. Related studies have been carried out in humans, but remain controversial.

Likewise, vibrations can form knots in rope-like molecules found inside cells. Dimitrii Makarov’s lab uses computer simulations of knotted molecules and precise mathematics, or knot theory, to investigate how molecules – DNA, RNA, and enzymes – become entangled and untangle.

DNA spontaneously knots all the time.

“Evolution has a beautiful solution for this,” said Makarov, “There are a host of enzymes in our cells that both cut the DNA and undo the knot so transcription can occur.”

There are many antibiotics and antitumor drugs that target these enzymes, blocking DNA replication and killing cells.

Makarov will describe one of the most complicated knots ever discovered in an enzyme called human ubiquitin hydrolase. He explained,

“The theory is that this large, bulky knot sits in the middle of the enzyme to prevent it from being degraded.”

Scientists however are still speculating about that.

This Tuesday, TSRC Town Talks brings Leitner and Makarov to the Historic Sheridan Opera House to present developing theories about how and why specific molecules behave.

For more information visit telluridescience.org.