Tag Archives: amino acid

Whale and calf.

A single ‘letter’ difference in their DNA made some whales huge, others sleek and predatory

A single-letter difference in their genetic code dictates whether a whale species will be sleek and slim — or big and fat.

Whale and calf.

No disrespect intended.
Image credits David Mark.

Genes dictate everything about how our bodies look, behave, and live. Changes in a genome, then, will have an effect on what the animal encoded by those genes ends up being. Even the minutest of changes can have a really big impact — case in point, cetaceans.

Huge results

A paper led by Liyuan Zhao, a marine biologist from Ocean University in China and co-authored by Roger Cone, an obesity researcher at and director of the University of Michigan Life Sciences Institute, reports that the variation of a single amino-acid in whales led some species to evolve muscular bodies and prey on fish and seals, while other species grew to be the biggest mammals alive today, filter-feeding on immense volumes of krill.

Cone has spent the better part of his career studying the melanocortin system. This is a collection of central nervous circuits dictates how much energy a body stores as fat. In humans, mutations affecting this system are one of the most common genetic causes of early-onset obesity, and it functions similarly in all mammals and fish. While at the lab for a visiting fellowship, Zhao picked up on the idea; given its central role in maintaining energy balance, she wanted to see if variations in genes affecting the melanocortin system could explain the evolution of such different feeding behaviors and body sizes in the two main whale suborders.

Odontoceti, such as dolphins and killer whales, hunt their meals and the smallest members of the suborder usually grow to around 1.5 m (5 ft.) in length. In stark contrast, Mysticeti, such as humpback or blue whales, are filter-feeders which can grow well over 30.5 m (100 ft.).

Tiny causes

Working together with co-author Antonis Rokas, a Professor at the Vanderbilt University of Nashville’s Department of Biological Sciences, the two obtained DNA samples of 20 whale species from an existing repository at NOAA’s Southwest Fisheries Science Center in La Jolla, California. They were looking for the genes encoding the MCR4 neuropeptide receptor (a key receptor in the melanocortin system) and found one single difference, which perfectly correlated with one of the two groups:

Odontoceti (toothed whales) have the amino-acid arginine (A) in position 156 of their genetic code. Mysticeti (baleen whales) have glutamine in the same position of the genome. The team tied glutamine in this position to an increased sensitivity of the MCR4 receptor to the transmitter molecule that activates it.

“Our data suggest that the melanocortin system is more highly regulated in whales that hunt — and, conversely, that the giant filter feeders may receive reduced satiety signals from this system,” Cone explains.

“This difference could well have played some role in the divergence of these two major types of cetaceans — and may help explain the differences in feeding behavior and amazing range of body sizes among whales, which is far greater than in any other type of mammal.”

The team’s main interest is to take the results from “bench to bedside” and apply them to human health. Cone also joked that the research could go from “bench to barnside,” as the U.S. Department of Agriculture and the United States-Israel Binational Agricultural Research and Development Fund have funded the lab to apply their insight into feeding and growth of different species to improve feed efficiency in fish farms.

The paper “Functional variants of the melanocortin-4 receptor associated with the Odontoceti and Mysticeti suborders of cetaceans” has been published in the journal Scientific Reports.

Early Earth wasn't the most hospitable place in the Universe, but some in all this chaos life emerged. Image credit: Peter Sawyer / Smithsonian Institution.

Tracking the origin of life: computer simulation delves inside ‘primordial soup’

Early Earth wasn't the most hospitable place in the Universe, but some in all this chaos life emerged. Image credit: Peter Sawyer / Smithsonian Institution.

Early Earth wasn’t the most hospitable place in the Universe, but some in all this chaos life emerged. Image credit: Peter Sawyer / Smithsonian Institution.

One of the most famous chemistry experiments of the last century was the ‘primordial soup’ project initiated by Stanley Miller. The chemist wanted to see what would happen if you mixed methane, ammonia and hydrogen – all substances readily available on Earth before life began – and zapped them with electricity, to create a phenomenon analogous to lightning which would have been pretty frequent during those times. He found that the gaseous mixture turned into a liquid rich with amino acids in a reaction channeled by the electricity. The amino acids are essential to life as we know it since these form proteins when snapped together. So, armed with this fantastic new found knowledge Miller hypothesized that since simple chemicals could be turned into biological molecules in a lab, then something similar may have led to the formation of life on Earth billions of years ago, with some added steps in between of course.

Looking for life in all the right places

Since then, the primordial soup experiment has been repeated countless times with variations as our understanding of the early Earth evolved. For instance, since Miller’s famous first tries in the 1950’s scientists today have made sugars and DNA building blocks, all just by starting from a suit of primordial chemical. It’s still unclear, however, what are the intermediary products and what are mechanics that eventually lead to biomolecules.

[ALSO READ] Diamonds hold the key to primordial life

Unlike Miller, scientists today have access to supercomputers that can keep track of many complicated interdependencies and relationships. Researchers in France used such a supercomputer to model how a couple of primordial chemicals interact and transform when subjected to an electric field of increasing strength. The model tracked the formation of intermediate molecules that eventually turned into glycine, a simple amino acid that often shows up in Miller-type experiments. Before glycine, however, the gases first joined to form formic acid and formamide.

We’re still a long way from being able to make actual life in a lab jar, but these more recent findings definitely help. In their paper, published in the journal Proceedings of the National Academy of Sciences, the scientists also outlined that astronomers might want to look for signs of these chemicals on Earth-like exoplanets – it might give them clues as to where it might be likely to find extraterrestrial life.

NASA researchers help explain why life is left-handed

Scientists that analyzed meteorite dust made some discoveries that gave them clues about the ever standing mystery of how life works at its most basic, molecular level. This question has puzzled researchers for quite a while now and definitive answers are yet to be found.

“We found more support for the idea that biological molecules, like amino acids, created in space and brought to Earth by meteorite impacts help explain why life is left-handed,” according to Dr. Daniel Glavin of NASA’s Goddard Space Flight Center in Greenbelt, Md. “By that I mean why all known life uses only left-handed versions of amino acids to build proteins.”

Proteins are life’s basic worker, used in basically everything, and they’re the building bricks of most structures. They’re made of amino acids arranged in a linear chain and joined together by peptide bonds. Also, despite the fact that there are only 20 amino acids, they can arrange in virtually any order and in any number, so you get a huge number of combinations. These amino acid molecules can be built in a mirror fashion, meaning that they can be built in two different directions that mirror each other. Life based on right handed amino acids should be just fine, only it’s not.

“If you do [right handed molecules], life turns to something resembling scrambled eggs — it’s a mess. Since life doesn’t work with a mixture of left-handed and right-handed amino acids, the mystery is: how did life decide — what made life choose left-handed amino acids over right-handed ones?

Over the last 4 years, scientists looked at sample meteorites with different amounts of water and looked particularily for an amino acid called isovaline because it has the ability to preserve its handedness for billions of years and there are very little chances that it would be contaminated by Earth life, because it’s extremely rarely used. If the original shift to “lefties” originated in space, the search for life in our solar system becomes much harder, but the probability of its origin becomes much more probable.

“If we find life anywhere else in our solar system, it will probably be microscopic, since microbes can survive in extreme environments,” said Dr. Jason Dworkin of NASA Goddard, co-author of the study. “One of the biggest problems in determining if microscopic life is truly extra-terrestrial is making sure the sample wasn’t contaminated by microbes brought from Earth. If we find the life is based on right-handed amino acids, then we know for sure it isn’t from Earth. However, if the bias toward left-handed amino acids began in space, it likely extends across the solar system, so any life we may find on Mars, for example, will also be left-handed. On the other hand, if there is a mechanism to choose handedness before life emerges, it is one less problem prebiotic chemistry has to solve before making life. If it was solved for Earth, it probably has been solved for the other places in our solar system where the recipe for life might exist, such as beneath the surface of Mars, or in potential oceans under the icy crust of Europa and Enceladus, or on Titan.”