2. MOLECULAR BIOLOGY
Molecular biology is the branch of biology that
deals with nature of biological phenomena at the
molecular level through the study of the DNA, RNA
and protein and other macromolecules
Molecular biology is the study of biomolecules and
biomolecular mechanisms that occur in living
organisms.
“Biochemistry of genes and their products”
Molecular biology finds its origin in the 1930s and
1940s.
The term “molecular biology” was first used in 1938
by Warren Weaver.
Warren Weaver
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5. Molecular biologist focus on two categories of macromolecules
particularly they are :
1) Nucleic acids, among which the most famous is
deoxyribonucleic acid (or DNA), the constituent of genes,
and
2) Proteins, which are the active agents of living organisms.
Scope of molecular biology therefore is to characterize the
structure, function and relationships between these two types
of macromolecules. This will suffice to allow us to establish a
date for the so-called "molecular revolution".
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9. In 1940, George Beadle and
Edward Tatum demonstrated the
existence of a precise relationship
between genes and proteins.
In the course of their experiments
connecting genetics with
biochemistry, they switched from
the genetics mainstay Drosophila
to a more appropriate model
organism, the fungus Neurospora;
the construction and exploitation
of new model organisms would
become a recurring theme in the
development of molecular biology.
George Wells
Beadle
Edward Lawrie
Tatum
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10. In 1944, Oswald Avery, working
at the Rockefeller Institute of New
York, demonstrated that genes
are made up of DNA.
In 1952, Alfred Hershey and
Martha Chase confirmed that the
genetic material of the
Bacteriophage, the virus which
infects bacteria, is made up of
DNA.
Oswald T. Avery
Alfred Hershey &
Martha Chase
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11. In 1953, James Watson and
Francis Crick discovered the
double helical structure of the DNA
molecule.
In 1961, Francois Jacob and
Jacques Monod hypothesized the
existence of an intermediary
between DNA and its protein
products, which they called
messenger RNA.
James Watson and
Francis Crick
Francois Jacob and
Jacques Monod
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12. Between 1961 and 1965, the relationship between
the information contained in DNA and the structure
of proteins was determined: there is a code, the
genetic code, which creates a correspondence
between the succession of nucleotides in the DNA
sequence and a series of amino acids in proteins.
At the beginning of the 1960s, Monod and Jacob
also demonstrated how certain specific proteins,
called regulative proteins, latch onto DNA at the
edges of the genes and control the transcription of
these genes into messenger RNA; they direct the
"expression" of the genes.
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13. History of DNA biochemistry
First isolation of DNA
Working in the 19th century,
biochemists initially isolated DNA and
RNA (mixed together) from cell nuclei.
But they realized later that nucleotides
were of two types
one containing ribose and, the other
deoxyribose.
It was this subsequent discovery that
led to the identification and naming of
DNA as a substance distinct from RNA.
Discovery of the DNA
Double Helix
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14. Friedrich Miescher (1844-1895)
discovered a substance called "nuclein"
in 1869. Somewhat later, he isolated a
pure sample known as DNA from the
sperm of salmon.
And in 1889 his pupil, Richard
Altmann, named it "nucleic acid". This
substance was found to exist only in
the chromosomes.
Friedrich Miescher
Richard Altmann
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15. In 1929 Phoebus Levene at the Rockefeller
Institute identified the components (the four
bases, the sugar and the phosphate chain) and
he showed that the components of DNA were
linked in the order phosphate-sugar-base.
He called each of these units a nucleotide and
suggested the DNA molecule consisted of a
string of nucleotide units linked together through
the phosphate groups, which are the 'backbone'
of the molecule.
Phoebus Levene
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16. However Levene thought the chain was short
and that the bases repeated in the same
fixed order.
Torbjorn Caspersson and Einar Hammersten
showed that DNA was a polymer.
Torbjorn Caspersson
Einar Hammersten
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17. Max Delbrück, Nikolai V. Timofeeff-
Ressovsky, and Karl G. Zimmer
published results in 1935 suggesting
that chromosomes are very large
molecules the structure of which can be
changed by treatment with X-rays, and
that by so changing their structure it
was possible to change the heritable
characteristics governed by those
chromosomes.
Max
Delbrück
Nikolai V. Timofeeff-Ressovsky
Karl G. Zimmer
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