was a pioneer Japanese

molecular biologist Molecular biology is the branch of biology that seeks to understand the molecular basis of biological activity in and between cells, including biomolecular synthesis, modification, mechanisms, and interactions. The study of chemical and physi ...

, known for his research on

DNA replication In molecular biology, DNA replication is the biological process of producing two identical replicas of DNA from one original DNA molecule. DNA replication occurs in all living organisms acting as the most essential part for biological inheritanc ...

and especially for describing the role of

Okazaki fragments Okazaki fragments are short sequences of DNA nucleotides (approximately 150 to 200 base pairs long in eukaryotes) which are synthesized discontinuously and later linked together by the enzyme DNA ligase to create the lagging strand during DNA r ...

along with his wife Tsuneko. Okazaki was born in

Hiroshima is the capital of Hiroshima Prefecture in Japan. , the city had an estimated population of 1,199,391. The gross domestic product (GDP) in Greater Hiroshima, Hiroshima Urban Employment Area, was US$61.3 billion as of 2010. Kazumi Matsui h ...

, Japan. He graduated in 1953 from

Nagoya University , abbreviated to or NU, is a Japanese national research university located in Chikusa-ku, Nagoya. It was the seventh Imperial University in Japan, one of the first five Designated National University and selected as a Top Type university of T ...

, and worked as a professor there after 1963. He died of

leukemia Leukemia ( also spelled leukaemia and pronounced ) is a group of blood cancers that usually begin in the bone marrow and result in high numbers of abnormal blood cells. These blood cells are not fully developed and are called ''blasts'' or ' ...

in 1975 at the age of 44 while traveling to the United States; he had been heavily

irradiated Irradiation is the process by which an object is exposed to radiation. The exposure can originate from various sources, including natural sources. Most frequently the term refers to ionizing radiation, and to a level of radiation that will serve ...

when the

first atomic bomb Trinity was the code name of the first detonation of a nuclear weapon. It was conducted by the United States Army at 5:29 a.m. on July 16, 1945, as part of the Manhattan Project. The test was conducted in the Jornada del Muerto desert a ...

was dropped.

Okazaki Fragments

In 1968, Reiji and

Tsuneko Okazaki is a Japanese pioneer of molecular biology known for her work on DNA replication and specifically for discovering Okazaki fragments, along with her husband Reiji. Dr. Tsuneko Okazaki has continued to be involved in academia, contributing to m ...

discovered the way in which the lagging strand of DNA is replicated via fragments, now called

. Their experiments used ''E. coli''. After introducing 3T-thymidine for only ten seconds to ''E. coli'' during DNA replication, they placed the sample in a test tube of alkaline sucrose. The larger, heavier DNA flowed to the bottom of the test tube, while the smaller, lighter DNA did not. When samples were taken from the bottom of the test tube, it was found that half were heavy and half were light, proving that half of the DNA was complete and half was in fragments. Then he took a sample of ''E. coli'' DNA that had been synthesized for an additional five seconds, and found all the activity now resulted in the larger molecular weight. This complete replacement of fragments was later identified as RNA primers being replaced with DNA nucleotides by

DNA polymerase I DNA polymerase I (or Pol I) is an enzyme that participates in the process of prokaryotic DNA replication. Discovered by Arthur Kornberg in 1956, it was the first known DNA polymerase (and the first known of any kind of polymerase). It was initiall ...

and Okazaki fragments being joined by

DNA ligase DNA ligase is a specific type of enzyme, a ligase, () that facilitates the joining of DNA strands together by catalyzing the formation of a phosphodiester bond. It plays a role in repairing single-strand breaks in duplex DNA in living organ ...

References

1930 births 1975 deaths Japanese biochemists Japanese molecular biologists People from Hiroshima Hibakusha Nagoya University faculty Nagoya University alumni {{japan-scientist-stub