Microbiology and Immunology

WORLD OF MICROBIOLOGY AND IMMUNOLOGY Wine making

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of bases—including the molecular compounds adenine,

thymine, guanine, and cytosine—inside, bonded by hydrogen.

It is important to note that while Wilkins’ contribution to the

discernment DNA’s structure is undeniable, controversy sur-

rounds how Watson and Crick obtained Franklin’s photo-

graphs and the fact that Franklin was not recognized for this

scientific breakthrough, particularly in terms of the Nobel

Prize. Because the Nobel Prize is not awarded posthumously,

Franklin, who died of cancer in 1958, did not receive the same

recognition as did Watson, Crick, and Wilkins.

The knowledge of the DNA structure, which has been

described as resembling a spiral staircase, has provided the

impetus for advanced research in the field of genetics. For

example, scientists can now determine predispositions for cer-

tain diseases based on the presence of certain genes. Also, the

exciting but sometimes controversial area of genetic engineer-

ing has developed.

Wilkins, Watson, and Crick were awarded the 1962

Nobel Prize for physiology or medicine for their work which

uncovered the structure of hereditary material DNA. After

winning the Nobel Prize, Wilkins focused next on elucidating

the structure of ribonucleic acids (RNA)—a compound like

DNA associated with the control of cellular chemical activi-

ties—and, later, nerve cell membranes. In 1962, Wilkins was

able to show that RNAalso had a helical structure somewhat

similar to that of DNA. Besides his directorship appointments

at the Medical Research Council’s Biophysics Unit, Wilkins

was also appointed director of the Council’s Neurobiology

Unit, a post he held from 1974 to 1980. Additionally, he was a

professor at King’s College, teaching molecular biologyfrom

1963 to 1970, and then biophysics as the department head

from 1970 to 1982. In 1981, he was named professor emeritus

at King’s College. Utilizing some of his professional expertise

for social causes, Wilkins has maintained membership in the

British Society for Social Responsibility in Science (of which

he is president), the Russell Committee against Chemical

Weapons, and Food and Disarmament International.

Wilkins is an honorary member of the American Society

of Biological Chemists and the American Academy of Arts

and Sciences. He was also honored with the 1960 Albert

Lasker Award of the American Public Health Association

(given jointly to Wilkins, Watson, and Crick), and was named

Fellow of the Royal Society of King’s College in 1959.

See alsoDNA (Deoxyribonucleic acid); DNA chips and micro

arrays; Gene; Genetic mapping; Molecular biology and

molecular genetics

WWine makingINE MAKING

Along with bread making, the use of the microorganisms

called yeasts to produce wine from grapes is one of the oldest

uses of microorganisms by man. The origins of wine making

date from antiquity. Before 2000 B.C. the Egyptians would

store crushed fruit in a warm place in order to produce a liq-

uid whose consumption produced feelings of euphoria. The

manufacture and consumption of wine rapidly became a part

of daily life in many areas of the Ancient world and eventually

became a well-established part of Classical civilization. For

centuries, wine making has been an important economic activ-

ity. In certain areas of the world, such as France, Italy, and

Northern California, wine making on a commercial scale is a

vital part of the local economy.

The agent of the formation of wine is yeast. Yeasts are

small, single-celled fungithat belong to the genus Ascomycota.

Hallmarks of yeast are their ability to reproduce by the meth-

ods of fission or budding, and their ability to utilize compounds

called carbohydrates (specifically the sugar glucose) with the

subsequent production of alcohol and the gas carbon dioxide.

This chemical process is called fermentation.

Yeast cells are able to carry out fermentation because of

enzymesthey possess. The conversion of sugar to alcohol ulti-

mately proves lethal to the yeast cells, which cannot tolerate

the increasing alcohol levels. Depending on the type of yeast

used, the alcohol content of the finished product can vary from

around 5% to over 20%, by volume.

The scientific roots of fermentation experimentation

date back to the seventeenth century. In 1680 Anton van

Leeuwenhoekused his hand-built light microscopes to detect

yeast. Almost one hundred years later the French chemist

Antoine Laurent Lavoisier proposed that yeast was the agent

of the fermentation of sugar. This was confirmed in 1935 by

the examination of yeast vats with the greatly improved

microscopes of that day.

In the nineteenth century the role of yeasts as a catalyst

(that is, as an agent that accelerates a chemical process with-

out itself being changed in the process) was recognized by the

Swedish chemist Jons Berzelius. In the 1860s the renowned

microbiologist Louis Pasteurdiscovered that yeast fermenta-

tion could proceed in the absence of oxygen. In 1878 Wilhelm

Kuhne recognized that the yeast catalyst was contained inside

the cell. He coined the term “enzyme” for the catalyst.

In fact more than two dozen yeast enzymes participate in

the degradation of glucose. The degradation is a pathway, with

one reaction being dependent on the occurrence of a prior reac-

tion, and itself being required for a subsequent reaction. In total

some 30 chemical reactions are involved. These reactions

require the function of the various enzymes. The yeast cell is

the biological machine that creates the enzymes. Once the

enzymes are present, alcoholic fermentation can proceed in the

absence of living yeast. Enzymes, however, have only a finite

period of activity before they themselves degrade. Hence a

continual supply of fresh enzymes requires living yeast.

Many types of yeast exist. The stable types suitable for

making wine (and bread and beer) are the seven species of

yeast belonging to the genus Saccharomyces. The name comes

from the Greek words for sugar (sacchar) and fungus (Mykes).

The predominant species in wine making is Saccharomyces

cerevisiae. There are multiple strains of this species that pro-

duce wine. The selectionof yeast type is part of the art of wine

making; the yeast is matched to the grape and the fermentation

conditions to produce—the wine maker hopes—a finished

product of exceptional quality.

The natural source of yeast for wine making is often the

population that becomes dominant in the vineyard. Less

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