Synthetic amino acid

 The invention :



Amethod for synthesizing amino acids by combining
water, hydrogen, methane, and ammonia and exposing the
mixture to an electric spark.



The people behind the invention : 



Stanley Lloyd Miller (1930- ), an American professor of
chemistry

Harold Clayton Urey (1893-1981), an American chemist who
won the 1934 Nobel Prize in Chemistry



Aleksandr Ivanovich Oparin (1894-1980), a Russian biochemist

John Burdon Sanderson Haldane (1892-1964), a British scientist







Prebiological Evolution



The origin of life on Earth has long been a tough problem for scientists

to solve. While most scientists can envision the development

of life through geologic time from simple single-cell bacteria

to complex mammals by the processes of mutation and natural selection,

they have found it difficult to develop a theory to define

how organic materials were first formed and organized into lifeforms.

This stage in the development of life before biologic systems

arose, which is called “chemical evolution,” occurred between

4.5 and 3.5 billion years ago. Although great advances in

genetics and biochemistry have shown the intricate workings of

the cell, relatively little light has been shed on the origins of this intricate

machinery of the cell. Some experiments, however, have

provided important data from which to build a scientific theory of

the origin of life. The first of these experiments was the classic

work of Stanley Lloyd Miller.

Miller worked with Harold Clayton Urey, a Nobel laureate, on the

environments of the early earth. John Burdon Sanderson Haldane, a

British biochemist, had suggested in 1929 that the earth’s early atmosphere

was a reducing one—that it contained no free oxygen. In

1952, Urey published a seminal work in planetology, The Planets, in

which he elaborated on Haldane’s suggestion, and he postulated

that the earth had formed from a cold stellar dust cloud. Urey

thought that the earth’s primordial atmosphere probably contained

elements in the approximate relative abundances found in the solar

system and the universe.

It had been discovered in 1929 that the Sun is approximately 87

percent hydrogen, and by 1935 it was known that hydrogen encompassed

the vast majority (92.8 percent) of atoms in the universe.

Urey reasoned that the earth’s early atmosphere contained mostly

hydrogen, with the oxygen, nitrogen, and carbon atoms chemically

bonded to hydrogen to form water, ammonia, and methane. Most

important, free oxygen could not exist in the presence of such an

abundance of hydrogen.

As early as the mid-1920’s, Aleksandr Ivanovich Oparin, a Russian

biochemist, had argued that the organic compounds necessary

for life had been built up on the early earth by chemical combinations

in a reducing atmosphere. The energy from the Sun would

have been sufficient to drive the reactions to produce life. Haldane

later proposed that the organic compounds would accumulate in

the oceans to produce a “dilute organic soup” and that life might

have arisen by some unknown process from that mixture of organic

compounds.





Primordial Soup in a Bottle



Miller combined the ideas of Oparin and Urey and designed a

simple, but elegant, experiment. He decided to mix the gases presumed

to exist in the early atmosphere (water vapor, hydrogen, ammonia,

and methane) and expose them to an electrical spark to determine

which, if any, organic compounds were formed. To do this,

he constructed a relatively simple system, essentially consisting of

two Pyrex flasks connected by tubing in a roughly circular pattern.

The water and gases in the smaller flask were boiled and the resulting

gas forced through the tubing into a larger flask that contained

tungsten electrodes. As the gases passed the electrodes, an electrical

spark was generated, and from this larger flask the gases and any

other compounds were condensed. The gases were recycled through

the system, whereas the organic compounds were trapped in the

bottom of the system.

Miller was trying to simulate conditions that had prevailed on

the early earth. During the one week of operation, Miller extracted

and analyzed the residue of compounds at the bottom of the system.

The results were truly astounding. He found that numerous organic

compounds had, indeed, been formed in only that one week. As

much as 15 percent of the carbon (originally in the gas methane) had

been combined into organic compounds, and at least 5 percent of

the carbon was incorporated into biochemically important compounds.

The most important compounds produced were some of

the twenty amino acids essential to life on Earth.

The formation of amino acids is significant because they are the

building blocks of proteins. Proteins consist of a specific sequence of

amino acids assembled into a well-defined pattern. Proteins are necessary

for life for two reasons. First, they are important structural

materials used to build the cells of the body. Second, the enzymes

that increase the rate of the multitude of biochemical reactions of life

are also proteins. Miller not only had produced proteins in the laboratory

but also had shown clearly that the precursors of proteins—

the amino acids—were easily formed in a reducing environment

with the appropriate energy.

Perhaps the most important aspect of the experiment was the

ease with which the amino acids were formed. Of all the thousands

of organic compounds that are known to chemists, amino acids

were among those that were formed by this simple experiment. This

strongly implied that one of the first steps in chemical evolution was

not only possible but also highly probable. All that was necessary

for the synthesis of amino acids were the common gases of the solar

system, a reducing environment, and an appropriate energy source,

all of which were present on early Earth.



Consequences



Miller opened an entirely new field of research with his pioneering

experiments. His results showed that much about chemical

evolution could be learned by experimentation in the laboratory.

As a result, Miller and many others soon tried variations on

his original experiment by altering the combination of gases, using

other gases, and trying other types of energy sources. Almost all

the essential amino acids have been produced in these laboratory

experiments.

Miller’s work was based on the presumed composition of the

primordial atmosphere of Earth. The composition of this atmosphere

was calculated on the basis of the abundance of elements

in the universe. If this reasoning is correct, then it is highly likely

that there are many other bodies in the universe that have similar

atmospheres and are near energy sources similar to the Sun.

Moreover, Miller’s experiment strongly suggests that amino acids,

and perhaps life as well, should have formed on other planets.



See also : Artificial hormone; Artificial kidney .



Further Reading :