exists in four types depending on differences in the nucleic acid’s bases (Watson
and Crick 1953).
Nucleic acid is a polynucleotide, or a polymer consisting of several nucleotides
linked together in a chain. While this chemical structure was at least partially
understood, the question of what function the material had and how it related to
genes remained to be solved.
2.5 The Gene Entity
Proof that nucleic acid stored genetic information came through a 1928 experiment
in trait transformation by Frederick Griffith. Griffith applied heat to kill pathogenic
pneumococcus bacteria responsible for pneumonia in mice. After mixing it with
non-pathogenic pneumococcus, he discovered the non-pathogenic strain had
become pathogenic. He concluded that the pathogenic strain contained a trait
transformation factor, which had entered the non-pathogenic strain and caused a
change in its properties. The nature of this trait transformation factor remained
uncertain for many years until 1944, when O. T. Avery and co-researchers purified
the factor from pathogenic pneumococcus and identified it as deoxyribonucleic acid
(DNA; see Table 2.1) (Griffith 1934; Avery et al. 1944).
After Avery’s experiment, questions arose as to whether DNA was a universal
genetic material, or whether proteins could also be responsible for genetic information. The answer to the question came from A. H. Hershey and M. Chase. In
1952, they performed an experiment using a T2 phage virus infecting E. coli
bacteria. Using isotopes, they marked the DNA with
32 P and the protein with
35 S
and infected bacteria (Fig. 2.7). Only the DNA marked with
32 P from the T2 phage
was injected into the E. coli; the protein was not introduced. After around 20 min,
they found that many offspring phages had been created and released from DNA
information within the bacterium. From this, they concluded that DNA, not proteins, was responsible for genetic information (Hershey et al. 1953).
Later, it was proven that DNA carried genetic information not only in
prokaryotes but also in eukaryotes. More recently, a general practice has arisen of
inserting chemically synthesized DNA into cells to create corresponding gene
products.
Table 2.1 Avery’s experimental findings
Bacteria transplanted to medium
Form and ratios of resulting
colonies
Live R type bacteria
R:S = 1,000,000:1
a
Killed S type bacteria
O
Mixture of live R type bacteria and killed S type
bacteria
R:S = 100:1
a S is believed to have arisen as a mutation of R
2.4 What Is Nucleic Acid?
33
and Crick 1953).
Nucleic acid is a polynucleotide, or a polymer consisting of several nucleotides
linked together in a chain. While this chemical structure was at least partially
understood, the question of what function the material had and how it related to
genes remained to be solved.
2.5 The Gene Entity
Proof that nucleic acid stored genetic information came through a 1928 experiment
in trait transformation by Frederick Griffith. Griffith applied heat to kill pathogenic
pneumococcus bacteria responsible for pneumonia in mice. After mixing it with
non-pathogenic pneumococcus, he discovered the non-pathogenic strain had
become pathogenic. He concluded that the pathogenic strain contained a trait
transformation factor, which had entered the non-pathogenic strain and caused a
change in its properties. The nature of this trait transformation factor remained
uncertain for many years until 1944, when O. T. Avery and co-researchers purified
the factor from pathogenic pneumococcus and identified it as deoxyribonucleic acid
(DNA; see Table 2.1) (Griffith 1934; Avery et al. 1944).
After Avery’s experiment, questions arose as to whether DNA was a universal
genetic material, or whether proteins could also be responsible for genetic information. The answer to the question came from A. H. Hershey and M. Chase. In
1952, they performed an experiment using a T2 phage virus infecting E. coli
bacteria. Using isotopes, they marked the DNA with
32 P and the protein with
35 S
and infected bacteria (Fig. 2.7). Only the DNA marked with
32 P from the T2 phage
was injected into the E. coli; the protein was not introduced. After around 20 min,
they found that many offspring phages had been created and released from DNA
information within the bacterium. From this, they concluded that DNA, not proteins, was responsible for genetic information (Hershey et al. 1953).
Later, it was proven that DNA carried genetic information not only in
prokaryotes but also in eukaryotes. More recently, a general practice has arisen of
inserting chemically synthesized DNA into cells to create corresponding gene
products.
Table 2.1 Avery’s experimental findings
Bacteria transplanted to medium
Form and ratios of resulting
colonies
Live R type bacteria
R:S = 1,000,000:1
a
Killed S type bacteria
O
Mixture of live R type bacteria and killed S type
bacteria
R:S = 100:1
a S is believed to have arisen as a mutation of R
2.4 What Is Nucleic Acid?
33