Microbiology and Immunology

WORLD OF MICROBIOLOGY AND IMMUNOLOGY Miller-Urey experiment

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used in other electronic equipment, such as a stereo. In addi-

tion, the sample preparation is usually less tedious. Many sam-

ples can be imaged in air with essentially no preparation. For

more sensitive samples that react with air, imaging is done in

vacuum. A requirement for the STM is that the samples be

electrically conducting, such as a metal.

There have been numerous variations on the types of

microscopy outlined so far. A sampling of these is: acoustic

microscopy, which involves the reflection of sound waves off

a specimen; x-ray microscopy, which involves the transmis-

sion of x rays through the specimen; near field optical

microscopy, which involves shining light through a small

opening smaller than the wavelength of light; and atomic force

microscopy, which is similar to scanning tunneling

microscopy but can be applied to materials that are not elec-

trically conducting, such as quartz.

One of the most amazing recent developments in

microscopy involves the manipulation of individual atoms.

Through a novel application of the STM, scientists at IBM

were able to arrange individual atoms on a surface and spell

out the letters “IBM.” This has opened up new directions in

microscopy, where the microscope is both an instrument with

which to observe and to interact with microscopic objects.

Future trends in microscopy will most likely probe features

within the atom.

See alsoElectron microscope, transmission and scanning;

Electron microscopic examination of microorganisms;

Laboratory techniques in immunology; Laboratory techniques

in microbiology

MMiller-Urey experimentILLER-UREY EXPERIMENT

A classic experiment in molecular biology, the Miller-Urey

experiment, established that the conditions that existed in

Earth’s primitive atmosphere were sufficient to produce amino

acids, the subunits of proteins comprising and required by liv-

ing organisms. In essence, the Miller-Urey experiment funda-

mentally established that Earth’s primitive atmosphere was

capable of producing the building blocks of life from inor-

ganic materials.

In 1953, University of Chicago researchers Stanley L.

Millerand Harold C. Urey set up an experimental investigation

into the molecular origins of life. Their innovative experimen-

tal design consisted of the introduction of the molecules

thought to exist in early Earth’s primitive atmosphere into a

closed chamber. Methane (CH 4 ), hydrogen (H 2 ), and ammonia

(NH 3 ) gases were introduced into a moist environment above

a water-containing flask. To simulate primitive lightning dis-

charges, Miller supplied the system with electrical current.

After a few days, Miller observed that the flask con-

tained organic compounds and that some of these compounds

were the amino acids that serve as the essential building

blocks of protein. Using chromatological analysis, Miller con-

tinued his experimental observations and confirmed the ready

formation of amino acids, hydroxy acids, and other organic

compounds.

Although the discovery of amino acid formation was of

tremendous significance in establishing that the raw materials

of proteins were easily to obtain in a primitive Earth environ-

ment, there remained a larger question as to the nature of the

origin of genetic materials mdash; in particular the origin of

DNAand RNAmolecules.

Continuing on the seminal work of Miller and Urey, in

the early 1960s Juan Oro discovered that the nucleotide base

adenine could also be synthesized under primitive Earth con-

ditions. Oro used a mixture of ammonia and hydrogen cyanide

(HCN) in a closed aqueous environment.

Oro’s findings of adenine, one of the four nitrogenous

bases that combine with a phosphate and a sugar (deoxyribose

for DNA and ribose for RNA) to form the nucleotides repre-

sented by the genetic code: (adenine (A), thymine (T), gua-

nine (G), and cytosine (C). In RNA molecules, the nitrogenous

base uracil (U) substitutes for thymine. Adenine is also a fun-

damental component of adenosine triphosphate (ATP), a mol-

ecule important in many genetic and cellular functions.

Subsequent research provided evidence of the forma-

tion of the other essential nitrogenous bases needed to con-

struct DNA and RNA.

Researcher using light microscope to examine cell cultures.

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