Microbiology and Immunology

Chase, Martha Cowles WORLD OF MICROBIOLOGY AND IMMUNOLOGY

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(water hating). These are hidden in the interior of a correctly

folded protein, exposing the hydrophilic (water loving) amino

acids to the watery interior solution of the cell. If folded in

such a correct manner, tensions are minimized and the three-

dimensional structure of the protein is stable. Chaperons func-

tion to aid the folding process, ensuring protein stability and

proper function.

Protein folding occurs by trial and error. If the protein

folds the wrong way, it is captured by a chaperone, and

another attempt at folding can occur. Even correctly folded

proteins are subject to external stress that can disrupt structure.

The chaperones, which are produced in greater amounts when

a cell is exposed to higher temperatures, function to stabilize

the unraveling proteins until the environmental crisis passes.

Non-biological molecules can also participate as chap-

erones. In this category, protein folding can be increased by

the addition of agents such as glycerol, guanidium chloride,

urea, and sodium chloride. Folding is likely due to an electro-

static interaction between exposed charged groups on the

unfolded protein and the anions.

Increasing attention is being paid to the potential roles of

chaperones in human diseases, including infection and idio-

pathic conditions such as arthritis and atherosclerosis. One sub-

group of chaperones, the chaperonins, has received the most

attention in this regard, because, in addition to facilitating pro-

tein folding, they also act as cell-to-cell signaling molecules.

See alsoProteins and enzymes

CChase, Martha CowlesHASE, MARTHACOWLES(1927- )

American geneticist

Martha Cowles Chase is remembered for a landmark experi-

ment in genetics carried out with American geneticist Alfred

Day Hershey(1908–1997). Their experiment indicated that,

contrary to prevailing opinion in 1952, DNAwas genetic mate-

rial. A year later, James D. Watsonand British biophysicist

Francis Crickproposed their double helical model for the

three-dimensional structure of structure of DNA. Hershey was

honored as one of the founders of molecular biology, and

shared the 1969 Nobel Prize in medicine or physiology with

Salvador Luria and Max Delbrück.

Martha Chase was born in Cleveland, Ohio. She earned a

bachelor’s degree from the College of Wooster in 1950 and her

doctoral degree from the University of Southern California in

1964. Having married and changed her name to Martha C.
      Epstein (Martha Cowles Chase Epstein), she later returned to
      Cleveland Heights, Ohio, where she lived with her father,
      Samuel W. Chase. After graduating from college, Chase worked
      as an assistant to Alfred Hershey at the Carnegie Institution of
      Washington in Cold Spring Harbor, New York. This was a crit-
      ical period in the history of modern genetics and the beginning
      of an entirely new phase of research that established the science
      of molecular biology. Including the name of an assistant or tech-
      nician on a publication, especially one that was certain to
      become a landmark in the history of molecular biology, was
      unusual during the 1960s. Thus, it is remarkable that Martha

Chase’s name is inextricably linked to all accounts of the path

to the demonstration that DNA is the genetic material.

During the 1940s, most chemists, physicists, and geneti-

cists thought that the genetic material must be a protein, but

research on the bacteriathat cause pneumoniasuggested the

nucleic acids played a fundamental role in inheritance. The

first well-known series of experiments to challenge the

assumption that genes must be proteins or nucleoproteins was

carried out by Oswald T. Avery(1877–1955) and his co-work-

ers Colin Macleod, and Maclyn McCartyin 1944. Avery’s work

was a refinement of observations previously reported in 1928

by Fred Griffith (1877–1941), a British bacteriologist. Avery

identified the transforming principle of bacterial types as

DNA and noted that further studies of the chemistry of DNA

were required in order to explain its biological activity.

Most geneticists were skeptical about the possibility

that DNA could serve as the genetic material until the results

of the Hershey-Chase experiments of 1952 were reported.

Their experiments indicated that bacteriophages (virusesthat

attack bacteria) might act like tiny syringes containing the

genetic material and the empty virus containers might remain

outside the bacterial cell after the genetic material of the virus

had been injected. To test this possibility, Hershey and Chase

used radioactive sulfur to label bacteriophageproteins and

radioactive phosphate to label their DNA. After allowing

viruses to attack the bacterial cells, the bacterial cultures were

spun in a blender and centrifuged in order to separate intact

bacteria from smaller particles.

Hershey and Chase found that most of the bacterio-

phage DNA remained with the bacterial cells while their pro-

tein coats were released into the medium. They concluded that

the protein played a role in adsorption to the bacteria and

helped inject the viral DNA into the bacterial cell. Thus, it was

the DNA that was involved in the growth and multiplication of

bacteriophage within the infected bacterial cell. Friends of

Alfred Hershey recalled that when he was asked for his con-

cept of the greatest scientific happiness, he said it would be to

have an experiment that works. The Hershey-Chase experi-

ments became a proverbial example of what his friends and

colleagues called “Hershey Heaven.”

See also Bacteriophage and bacteriophage typing; DNA

(Deoxyribonucleic acid); Molecular biology and molecular

genetics; Molecular biology, central dogma of; Viral genetics

CChemical mutagenesisHEMICAL MUTAGENESIS

The interaction of certain environmental chemical compounds

and cell metabolismmay result in genetic changes in DNA

structure, affecting one or more genes. These chemical-

induced mutationsare known as chemical mutagenesis. Many

cancers and other degenerative diseases result from acquired

genetic mutations due to environmental exposure, and not as

an outcome of inherited traits. Chemicals capable of inducing

genetic mutation (i.e., chemical mutagenes or genotoxic com-

pounds) are present in both natural and man-made environ-

ments and products.

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