On this day in science history: Mars 5 launched

In 1973, the USSR launched Mars 5, on a Proton SL-12/D-1-e booster. It was one of several Soviet Mars probes – Mars 4, 5, 6, and 7 – launched in Jul-Aug 1973. The Mars 5 mission was to orbit Mars, which was achieved on 12 Feb 1974. Each orbit took about 25 hours. It was designed to return information on the composition, structure, and properties of the martian atmosphere and surface. However, after only 22 orbits, the mission ended prematurely due to loss of pressurization in the transmitter housing. Before the failure, data for a small portion of the martian southern hemisphere was captured with about 60 images forwarded over a nine day period. The probe also sent more measurements made by other instruments.
Mars in natural colour in 2007. By ESA – European Space Agency & Max-Planck Institute for Solar System Research for OSIRIS Team ESA/MPS/UPD/LAM/IAA/RSSD/INTA/UPM/DASP/IDA [CC BY-SA 3.0-igo (http://ift.tt/1wBCVB0)], via Wikimedia Commons
Mars is the fourth planet from the Sun and the second-smallest planet in the Solar System, after Mercury. Named after the Roman god of war, it is often referred to as the “Red Planet” because the iron oxide prevalent on its surface gives it a reddish appearance. Mars is a terrestrial planet with a thin atmosphere, having surface features reminiscent both of the impact craters of the Moon and the valleys, deserts, and polar ice caps of Earth.
The rotational period and seasonal cycles of Mars are likewise similar to those of Earth, as is the tilt that produces the seasons. Mars is the site of Olympus Mons, the largest volcano and second-highest known mountain in the Solar System, and of Valles Marineris, one of the largest canyons in the Solar System. The smooth Borealis basin in the northern hemisphere covers 40% of the planet and may be a giant impact feature. Mars has two moons, Phobos and Deimos, which are small and irregularly shaped. These may be captured asteroids, similar to 5261 Eureka, a Mars trojan.
There are ongoing investigations assessing the past habitability potential of Mars, as well as the possibility of extant life. Liquid water cannot exist on the surface of Mars due to low atmospheric pressure, which is less than 1% of the Earth’s, except at the lowest elevations for short periods. The two polar ice caps appear to be made largely of water. The volume of water ice in the south polar ice cap, if melted, would be sufficient to cover the entire planetary surface to a depth of 11 meters (36 ft). In November 2016, NASA reported finding a large amount of underground ice in the Utopia Planitia region of Mars. 
The volume of water detected has been estimated to be equivalent to the volume of water in Lake Superior.
Mars can easily be seen from Earth with the naked eye, as can its reddish coloring. Its apparent magnitude reaches −2.91, which is surpassed only by Jupiter, Venus, the Moon, and the Sun. Optical ground-based telescopes are typically limited to resolving features about 300 kilometers (190 mi) across when Earth and Mars are closest because of Earth’s atmosphere.
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Drinking coffee could lead to a longer life, scientist says

Here’s another reason to start the day with a cup of joe: Scientists have found that people who drink coffee appear to live longer.
Drinking coffee was associated with a lower risk of death due to heart disease, cancer, stroke, diabetes, and respiratory and kidney disease for African-Americans, Japanese-Americans, Latinos and whites.
People who consumed a cup of coffee a day were 12 percent less likely to die compared to those who didn’t drink coffee. This association was even stronger for those who drank two to three cups a day – 18 percent reduced chance of death.
Lower mortality was present regardless of whether people drank regular or decaffeinated coffee, suggesting the association is not tied to caffeine, said Veronica W. Setiawan, lead author of the study and an associate professor of preventive medicine at the Keck School of Medicine of USC.
A small cup of coffee. By Julius Schorzman (Own work) [CC BY-SA 2.0 (http://ift.tt/KcQbXG)], via Wikimedia Commons
“We cannot say drinking coffee will prolong your life, but we see an association,” Setiawan said. “If you like to drink coffee, drink up! If you’re not a coffee drinker, then you need to consider if you should start.”
The study, which will be published in the July 11 issue of Annals of Internal Medicine, used data from the Multiethnic Cohort Study, a collaborative effort between the University of Hawaii Cancer Centre and the Keck School of Medicine.
The ongoing Multiethnic Cohort Study has more than 215,000 participants and bills itself as the most ethnically diverse study examining lifestyle risk factors that may lead to cancer.
“Until now, few data have been available on the association between coffee consumption and mortality in non-whites in the United States and elsewhere,” the study stated. “Such investigations are important because lifestyle patterns and disease risks can vary substantially across racial and ethnic backgrounds, and findings in one group may not necessarily apply to others.”
Since the association was seen in four different ethnicities, Setiawan said it is safe to say the results apply to other groups.
“This study is the largest of its kind and includes minorities who have very different lifestyles,” Setiawan said. “Seeing a similar pattern across different populations gives stronger biological backing to the argument that coffee is good for you whether you are white, African-American, Latino or Asian.”
Previous research by USC and others have indicated that drinking coffee is associated with reduced risk of several types of cancer, diabetes, liver disease, Parkinson’s disease, Type 2 diabetes and other chronic diseases.
Setiawan, who drinks one to two cups of coffee daily, said any positive effects from drinking coffee are far-reaching because of the number of people who enjoy or rely on the beverage every day.
“Coffee contains a lot of antioxidants and phenolic compounds that play an important role in cancer prevention,” Setiawan said. “Although this study does not show causation or point to what chemicals in coffee may have this ‘elixir effect,’ it is clear that coffee can be incorporated into a healthy diet and lifestyle.”
About 62 percent of Americans drink coffee daily, a 5 percent increase from 2016 numbers, reported the National Coffee Association.
As a research institution, USC has scientists from across disciplines working to find a cure for cancer and better ways for people to manage the disease.
The Keck School of Medicine and USC Norris Comprehensive Cancer Center manage a state-mandated database called the Los Angeles Cancer Surveillance Program, which provides scientists with essential statistics on cancer for a diverse population.
Researchers from the USC Norris Comprehensive Cancer Center have found that drinking coffee lowers the risk of colorectal cancer.
But drinking piping hot coffee or beverages probably causes cancer in the esophagus, according to a World Health Organization panel of scientists that included Mariana Stern from the Keck School of Medicine.
In some respects, coffee is regaining its honor for wellness benefits. After 25 years of labelling coffee a carcinogen linked to bladder cancer, the World Health Organization last year announced that drinking coffee reduces the risk for liver and uterine cancer.
“Some people worry drinking coffee can be bad for you because it might increase the risk of heart disease, stunt growth or lead to stomach ulcers and heartburn,” Setiawan said. “But research on coffee have mostly shown no harm to people’s health.”
Setiawan and her colleagues examined the data of 185,855 African-Americans (17 percent), Native Hawaiians (7 percent), Japanese-Americans (29 percent), Latinos (22 percent) and whites (25 percent) ages 45 to 75 at recruitment. Participants answered questionnaires about diet, lifestyle, and family and personal medical history.
They reported their coffee drinking habits when they entered the study and updated them about every five years, checking one of nine boxes that ranged from “never or hardly ever” to “4 or more cups daily.” They also reported whether they drank caffeinated or decaffeinated coffee. The average follow-up period was 16 years.
Sixteen percent of participants reported that they did not drink coffee, 31 percent drank one cup per day, 25 percent drank two to three cups per day and 7 percent drank four or more cups per day. The remaining 21 percent had irregular coffee consumption habits.
Over the course of the study, 58,397 participants – about 31 percent – died. Cardiovascular disease (36 percent) and cancer (31 percent) were the leading killers.
The data was adjusted for age, sex, ethnicity, smoking habits, education, pre-existing disease, vigorous physical exercise and alcohol consumption.
Setiawan’s previous research found that coffee reduces the risk of liver cancer and chronic liver disease. She is currently examining how coffee is associated with the risk of developing specific cancers.
Researchers from the University of Hawaii Cancer Centre and the National Cancer Institute contributed to this study. The study used data from the Multiethnic Cohort Study, which is supported by a $19,008,359 grant from the National Cancer Institute of the National Institutes of Health.
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On this day in science history: the earliest recorded confirmed total solar eclipse occurred

In 709 BC, the earliest record of a confirmed total solar eclipse was written in China. From: Ch’un-ch’iu, book I: “Duke Huan, 3rd year, 7th month, day jen-ch’en, the first day (of the month). The Sun was eclipsed and it was total.” This is the earliest direct allusion to a complete obscuration of the Sun in any civilisation. The recorded date, when reduced to the Julian calendar, agrees exactly with that of a computed solar eclipse. Reference to the same eclipse appears in the Han-shu (‘History of the Former Han Dynasty’) (Chinese, 1st century AD): “…the eclipse threaded centrally through the Sun; above and below it was yellow.” Earlier Chinese writings that refer to an eclipse do so without noting totality.
Total Solar Eclipse. I, Luc Viatour [GFDL (http://ift.tt/KbUOlc), CC-BY-SA-3.0 (http://ift.tt/gc84jZ) or CC BY-SA 2.5-2.0-1.0 (http://ift.tt/Xoxvyb)], via Wikimedia Commons
Having fascinated mankind for years, the Sun is the star at the centre of the Solar System. It is a nearly perfect sphere of hot plasma, with internal convective motion that generates a magnetic field via a dynamo process. It is by far the most important source of energy for life on Earth. Its diameter is about 109 times that of Earth, and its mass is about 330,000 times that of Earth, accounting for about 99.86% of the total mass of the Solar System. About three quarters of the Sun’s mass consists of hydrogen (~73%); the rest is mostly helium (~25%), with much smaller quantities of heavier elements, including oxygen, carbon, neon, and iron.
The Sun is a G-type main-sequence star (G2V) based on its spectral class. As such, it is informally referred to as a yellow dwarf. It formed approximately 4.6 billion years ago from the gravitational collapse of matter within a region of a large molecular cloud. Most of this matter gathered in the center, whereas the rest flattened into an orbiting disk that became the Solar System. The central mass became so hot and dense that it eventually initiated nuclear fusion in its core. It is thought that almost all stars form by this process.
The Sun is roughly middle-aged; it has not changed dramatically for more than four billion years, and will remain fairly stable for more than another five billion years. After hydrogen fusion in its core has diminished to the point at which it is no longer in hydrostatic equilibrium, the core of the Sun will experience a marked increase in density and temperature while its outer layers expand to eventually become a red giant. It is calculated that the Sun will become sufficiently large to engulf the current orbits of Mercury and Venus, and render Earth uninhabitable.
The enormous effect of the Sun on Earth has been recognized since prehistoric times, and the Sun has been regarded by some cultures as a deity. The synodic rotation of Earth and its orbit around the Sun are the basis of the solar calendar, which is the predominant calendar in use today.
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Reconciling predictions of climate change

Harvard University researchers have resolved a conflict in estimates of how much the Earth will warm in response to a doubling of carbon dioxide in the atmosphere.
That conflict – between temperature ranges based on global climate models and paleoclimate records and ranges generated from historical observations – prevented the United Nations’ Intergovernmental Panel on Climate Change (IPCC) from providing a best estimate in its most recent report for how much the Earth will warm as a result of a doubling of CO2 emissions.
The researchers found that the low range of temperature increase – between 1 and 3 degrees Celsius – offered by the historical observations did not take into account long-term warming patterns. When these patterns are taken into account, the researchers found that not only do temperatures fall within the canonical range of 1.5 to 4.5 degrees Celsius but that even higher ranges, perhaps up to 6 degrees, may also be possible.
The research is published in Science Advances.
CO2 in Earth’s atmosphere if half of global-warming emissions are not absorbed (NASA simulation). By NASA/GSFC [Public domain], via Wikimedia Commons
It’s well documented that different parts of the planet warm at different speeds. The land over the northern hemisphere, for example, warms significantly faster than water in the Southern Ocean.
“The historical pattern of warming is that most of the warming has occurred over land, in particular over the northern hemisphere,” said Cristian Proistosescu, PhD ’17, and first author of the paper. “This pattern of warming is known as the fast mode – you put CO2 in the atmosphere and very quickly after that, the land in the northern hemisphere is going to warm.”
But there is also a slow mode of warming, which can take centuries to realize. That warming, which is most associated with the Southern Ocean and the Eastern Equatorial Pacific, comes with positive feedback loops that amplify the process. For example, as the oceans warm, cloud cover decreases and a white reflecting surface is replaced with a dark absorbent surface.
The researchers developed a mathematical model to parse the two different modes within different climate models.
“The models simulate a warming pattern like today’s, but indicate that strong feedbacks kick in when the Southern Ocean and Eastern Equatorial Pacific eventually warm, leading to higher overall temperatures than would simply be extrapolated from the warming seen to date,” said Peter Huybers, Professor of Earth and Planetary Sciences and of Environmental Science and Engineering at the Harvard John A. Paulson School of Engineering and Applied Sciences (SEAS) and co-author of the paper.
Huybers and Proistosescu found that while the slow mode of warming contributes a great deal to the ultimate amount of global warming, it is barely present in present-day warming patterns. “Historical observations give us a lot of insight into how climate changes and are an important test of our climate models,” said Huybers, “but there is no perfect analogue for the changes that are coming.”
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On this day in science history: foam rubber was developed

In 1929, foam rubber was developed at the Dunlop Latex Development Laboratories in Birmingham. British scientist E.A. Murphy whipped up the first batch in 1929, using an ordinary kitchen mixer to froth natural latex rubber. His colleagues were unimpressed – until they sat on it. Within five years it was everywhere, on motorcycle seats, on London bus seats, Shakespeare Memorial Theatre seats, and eventually in mattresses.
In 1937 isocyanate based materials were first used for the formation of foam rubbers, after World War II styrene-butadiene rubber replaced many natural types of foam. Foam rubbers have been used commercially for a wide range of applications since around the 1940s. There are two types of foam in use today. One is flexible foam and the other is rigid foam. The flexible version of the foam is used in furniture, car seats, to insulate walls, and even in the very shoes that we wear. The rigid form of foam rubber is used in insulating buildings, appliances like freezers and refrigeration trucks. 
Foam rubber mattress [Public domain], via Wikimedia Commons
So, how is foam rubber manufactured? Rates of polymerization can range from many minutes to just a few seconds. Fast reacting polymers feature short cycle periods and require the use of machinery to thoroughly mix the reacting agents. Slow polymers may be mixed by hand, but require long periods on mixing. As a result industrial application tends to use machinery to mix products. Product processing can range from a variety of techniques including, but not limited to spraying, open pouring, and molding.
  • Material preparation – Liquid and solid material generally arrive on location via rail or truck, once unloaded liquid materials are stored in heated tanks. When producing slabstock  typically two or more polymers streams are used.
  • Mixing – Open pouring, better known as continuous dispensing is used primarily in the formation of rigid, low density foams. Specific amounts of chemicals are mixed into a mixing head, much like an industrial blender. The foam is poured onto a conveyor belt, where it then cures for cutting.
  • Curing and Cutting – After curing on the conveyor belt the foam is then forced through a horizontal band saw. This band saw cuts the pieces in a set size for the application. General contracting uses 4’x12’x2’’.
  • Further processing – Once cut and cured the slabstock can either be sold or a lamination process can be applied. This process turns the slabstock into a rigid foam board known as boardstock. Boardstock is used for metal roof insulation, oven insulation, and many other durable goods.
Unfortunately, because of the variety in polyurethane chemistries, it is difficult to recycle foam materials using a single method. Reusing slab stock foams for carpet backing is how the majority of recycling is done. This method involves shredding the scrap and bonding the small flakes together to form sheets. Other methods involve breaking the foam down into granules and dispersing them into a polyol blend to be molded into the same part as the original. The recycling process is still ever developing for foam rubber and the future will hopefully unveil new and easier ways for recycling.
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Tipping points are real: Gradual changes in CO2 levels can induce abrupt climate changes

During the last glacial period, within only a few decades the influence of atmospheric CO2 on the North Atlantic circulation resulted in temperature increases of up to 10 degrees Celsius in Greenland – as indicated by new climate calculations from researchers at the Alfred Wegener Institute and the University of Cardiff. Their study is the first to confirm that there have been situations in our planet’s history in which gradually rising CO2 concentrations have set off abrupt changes in ocean circulation and climate at “tipping points.” These sudden changes, referred to as Dansgaard-Oeschger events, have been observed in ice cores collected in Greenland. The results of the study have just been released in the journal Nature Geoscience.
Ice core sample taken from drill. Photo by Lonnie Thompson, Byrd Polar Research Center, Ohio State University. [Public domain], via Wikimedia Commons
Previous glacial periods were characterised by several abrupt climate changes in the high latitudes of the Northern Hemisphere. However, the cause of these past phenomena remains unclear. In an attempt to better grasp the role of CO2 in this context, scientists from the Alfred Wegener Institute, Helmholtz Centre for Polar and Marine Research (AWI) recently conducted a series of experiments using a coupled atmosphere-ocean-sea ice model.
First author Xu Zhang explains: “With this study, we’ve managed to show for the first time how gradual increases of CO2 triggered rapid warming.” This temperature rise is the result of interactions between ocean currents and the atmosphere, which the scientists used the climate model to explore. According to their findings, the increased CO2 intensifies the trade winds over Central America, as the eastern Pacific is warmed more than the western Atlantic. This is turn produces increased moisture transport from the Atlantic, and with it, an increase in the salinity and density of the surface water. Finally, these changes lead to an abrupt amplification of the large-scale overturning circulation in the Atlantic. “Our simulations indicate that even small changes in the CO2 concentration suffice to change the circulation pattern, which can end in sudden temperature increases,” says Zhang.
Further, the study’s authors reveal that rising CO2 levels are the dominant cause of changed ocean currents during the transitions between glacial and interglacial periods. As climate researcher Gerrit Lohmann explains, “We can’t say for certain whether rising CO2 levels will produce similar effects in the future, because the framework conditions today differ from those in a glacial period. That being said, we’ve now confirmed that there have definitely been abrupt climate changes in the Earth’s past that were the result of continually rising CO2 concentrations.”
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Solar paint offers endless energy from water vapor

Researchers have developed a
solar paint that can absorb water vapour and split it to generate hydrogen –
the cleanest source of energy.
The paint contains a newly
developed compound that acts like silica gel, which is used in sachets to
absorb moisture and keep food, medicines and electronics fresh and dry.
Sun with sunspots and limb darkening as seen in visible light with solar filter. By Geoff Elston [CC BY 4.0 (http://ift.tt/1eRPUFd)], via Wikimedia Commons
But unlike silica gel, the new
material, synthetic molybdenum-sulphide, also acts as a semi-conductor and
catalyses the splitting of water molecules into hydrogen and oxygen.
Lead researcher Dr Torben
Daeneke, from RMIT University in Melbourne, Australia, said: “We found
that mixing the compound with titanium oxide particles leads to a
sunlight-absorbing paint that produces hydrogen fuel from solar energy and
moist air.
“Titanium oxide is the
white pigment that is already commonly used in wall paint, meaning that the
simple addition of the new material can convert a brick wall into energy
harvesting and fuel production real estate.
“Our new development has
a big range of advantages,” he said. “There’s no need for clean or
filtered water to feed the system. Any place that has water vapour in the air,
even remote areas far from water, can produce fuel.”
His colleague, Distinguished
Professor Kourosh Kalantar-zadeh, said hydrogen was the cleanest source of
energy and could be used in fuel cells as well as conventional combustion
engines as an alternative to fossil fuels.
“This system can also be
used in very dry but hot climates near oceans. The sea water is evaporated by
the hot sunlight and the vapour can then be absorbed to produce fuel.
“This is an extraordinary
concept – making fuel from the sun and water vapour in the air.”
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Which Earth-Size Planets are Habitable?

A University of Oklahoma
post-doctoral astrophysics researcher, Billy Quarles, has identified the possible
compositions of the seven planets in the TRAPPIST-1 system. Using thousands of
numerical simulations to identify the planets stable for millions of years,
Quarles concluded that six of the seven planets are consistent with an
Earth-like composition. The exception is TRAPPIST-1f, which has a mass of 25
percent water, suggesting that TRAPPIST-1e may be the best candidate for future
habitability studies.
“The goal of exoplanetary
astronomy is to find planets that are similar to Earth in composition and potentially
habitable,” said Quarles. “For thousands of years, astronomers have
sought other worlds capable of sustaining life.”
The Earth seen from space, by NASA/Apollo 17 crew; taken by either Harrison Schmitt or Ron Evans [Public domain or Public domain], via Wikimedia Commons
Quarles, a researcher in the
Homer L. Dodge Department of Physics and Astronomy, OU College of Arts and
Sciences, collaborated with scientists, E.V. Quintana, E. Lopez, J.E. Schlieder
and T. Barclay at NASA Goddard Space Flight Center on the project. Numerical
simulations for this project were performed using the Pleiades Supercomputer
provided by the NASA High-End Computing Program through the Ames Research
Center and at the OU Supercomputing Center for Education and Research.
TRAPPIST-1 planets are more
tightly spaced than in Kepler systems, which allow for transit timing
variations with the photometric observations. These variations tell the
researchers about the mass of the planets and the radii are measured through
the eclipses. Mass and radius measurements can then infer the density. By
comparing Earth’s density (mostly rock) to the TRAPPIST-1 planets, Quarles can
determine what the planets are likely composed of and provide insight into
whether they are potentially habitable.
TRAPPIST-1f has the tightest
constraints with 25 percent of its mass in water, which is rare given its
radius. The concern of this planet is that the mass is 70 percent the mass of
Earth, but it is the same size as Earth. Because the radius is so large, the
pressure turns the water to steam, and it is likely too hot for life as we know
it. The search for planets with a composition as close to Earth’s as possible
is key for finding places that we could identify as being habitable. Quarles
said he is continually learning about the planets and will investigate them
further in his studies.
TRAPPIST-1 is a nearby ultra-cool
dwarf about 40 light-years away from Earth and host to a remarkable planetary
system consisting of seven transiting planets. The seven planets are known as
TRAPPIST 1b, c, d, e, f, g and h.
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On this day in science – the rubber fire hose was patented

In 1821, a fire hose of cotton
web lined with rubber was patented by James Boyd of Boston, Mass. He invented
it to replace riveted leather hose. Leather hose had many drawbacks, including
drying out, cracking and bursting from excessive pressure. The introduction of
rivets (1807), to replace stitching, had allowed higher pressures and greater
delivery of water on the fireground. The improved hose now was 40 to 50 feet in
length and weighed more than 85 pounds with the couplings. Hose oilers were
developed to keep the leather supple and pliable. Various types of oils and
other substances were used to keep the hose in shape. By 1871, the Cincinnati
Fire Department was using the B.F. Goodrich Company’s new rubber hose
reinforced with cotton ply.
Indoor fire hose with a fire extinguisher, by Raysonho @ Open Grid Scheduler / Grid Engine (Own work) [CC0], via Wikimedia Commons
Modern fire hoses use a
variety of natural and synthetic fabrics and elastomers in their construction.
These materials allow the hoses to be stored wet without rotting and to resist
the damaging effects of exposure to sunlight and chemicals. Modern hoses are
also lighter weight than older designs, and this has helped reduce the physical
strain on firefighters. 
Various devices
are becoming more prevalent that remove the air from the interior of fire hose,
commonly referred to as fire hose vacuums. This process makes hoses smaller and
somewhat rigid, thus allowing more fire hose to be packed or loaded into the
same compartment on a fire fighting apparatus.
There are several types of
hose designed specifically for the fire service. Those designed to operate
under positive pressure are called discharge hoses. They include attack hose,
supply hose, relay hose, forestry hose, and booster hose. Those designed to operate
under negative pressure are called suction hoses.
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A guide to the twenty common amino acids

Have you ever thought about
what makes up your body? Only 20 amino acids! Take a look at the graphic below,
to discover the structure of each of these, plus information on the notation
used to represent them.
Source: Compound Interest. Click to enlarge.
Amino acids are organic
compounds containing amine (-NH2) and carboxyl (-COOH) functional groups, along
with a side chain (R group) specific to each amino acid. The key elements of an
amino acid are carbon, hydrogen, oxygen, and nitrogen, although other elements
are found in the side chains of certain amino acids. About 500 amino acids are
known and can be classified in many ways. They can be classified according to
the core structural functional groups’ locations as alpha- (α-), beta- (β-),
gamma- (γ-) or delta- (δ-) amino acids; other categories relate to polarity, pH
level, and side chain group type (aliphatic, acyclic, aromatic, containing
hydroxyl or sulfur, etc.). In the form of proteins, amino acid residues form
the second-largest component (water is the largest) of human muscles and other
tissues. Beyond their role as residues in proteins, amino acids participate in
a number of processes such as neurotransmitter transport and biosynthesis.
In biochemistry, amino acids
having both the amine and the carboxylic acid groups attached to the first
(alpha-) carbon atom have particular importance. They are known as 2-, alpha-,
or α-amino acids (generic formula H2NCHRCOOH in most cases, where R is an
organic substituent known as a “side chain”); often the term
“amino acid” is used to refer specifically to these. They include the
22 proteinogenic (“protein-building”) amino acids, which combine into
peptide chains (“polypeptides”) to form the building-blocks of a vast
array of proteins. These are all L-stereoisomers (“left-handed”
isomers), although a few D-amino acids (“right-handed”) occur in
bacterial envelopes, as a neuromodulator (D-serine), and in some antibiotics. 

Twenty of the proteinogenic amino acids are encoded directly by triplet codons
in the genetic code and are known as “standard” amino acids. The
other two (“non-standard” or “non-canonical”) are
selenocysteine (present in many noneukaryotes as well as most eukaryotes, but
not coded directly by DNA), and pyrrolysine (found only in some archea and one
bacterium). Pyrrolysine and selenocysteine are encoded via variant codons; for
example, selenocysteine is encoded by stop codon and SECIS element.
N-formylmethionine (which is often the initial amino acid of proteins in
bacteria, mitochondria, and chloroplasts) is generally considered as a form of
methionine rather than as a separate proteinogenic amino acid. Codon–tRNA
combinations not found in nature can also be used to “expand” the
genetic code and create novel proteins known as alloproteins incorporating
non-proteinogenic amino acids.
Many important proteinogenic
and non-proteinogenic amino acids have biological functions. For example, in
the human brain, glutamate (standard glutamic acid) and gamma-amino-butyric
acid (“GABA”, non-standard gamma-amino acid) are, respectively, the
main excitatory and inhibitory neurotransmitters. Hydroxyproline, a major
component of the connective tissue collagen, is synthesised from proline.
Glycine is a biosynthetic precursor to porphyrins used in red blood cells.
Carnitine is used in lipid transport.
Nine proteinogenic amino acids
are called “essential” for humans because they cannot be created from
other compounds by the human body and so must be taken in as food. Others may
be conditionally essential for certain ages or medical conditions. Essential
amino acids may also differ between species.

Because of their biological
significance, amino acids are important in nutrition and are commonly used in
nutritional supplements, fertilizers, and food technology. Industrial uses
include the production of drugs, biodegradable plastics, and chiral catalysts.
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