DNA Replication

Initiation:

            The initiation point where the splitting starts is called "origin of replication". The structure that is created is known as "Replication Fork".

            A helicase is the enzyme that splits the two strands. Thereafter, single-strand binding proteins (SSB) swiftly bind to the separated DNA, thus preventing the strands from reuniting. A primase, which generates an RNA primer to be used in DNA replication. RNA Primase can attract RNA nucleotides which bind to the DNA nucleotides of the 3'-5' strand due to the hydrogen bonds between the bases.

Elongation:

            The elongation process is different for the 5'-3' and 3'-5' template. The leading strand is synthesized continuously in the 5'-3' direction by DNA polymeraseIII. The lagging strand is synthesized discontinuously Primase synthesizes a short RNA primer, which is extended by DNA polymeraseIII to form an Okazaki fragment.In the lagging strand the DNA Polymerase I  reads the fragments and removes the RNA Primers. DNA Ligase joins in the Okazaki fragment to growing the strand.

            Each new double helix is consisted of one old and one new chain. This is what we call semiconservative replication.

Termination:

            The last step of DNA Replication is the Termination. This process happens when the DNA Polymerase reaches to an end of the strands. We can easily understand that in the last section of the lagging strand, when the RNA primer is removed, it is not possible for the DNA Polymerase to seal the gap (because there is no primer). So, the end of the parental strand where the last primer binds isn't replicated. These ends of linear (chromosomal) DNA consists of noncoding DNA that contains repeat sequences and are called telomeres. As a result, a part of the telomere is removed in every cycle of DNA Replication.

            The DNA Replication is not completed before a mechanism of repair fixes possible errors caused during the replication. Enzymes like nucleases remove the wrong nucleotides and the DNA Polymerase fills the gaps.


Role of enzymes:

           The enzyme helicase seperates the DNA helix so the DNA can be replicated. The enzyme polymerase matches up the new nucleotide bases to the original bases (during replication) and the enzyme ligase "mends" or "glues" the phosphate "backbone" into place with the new nucleotide bases forming a replication of the original DNA strand. (Whichever strand was replicated at the time).

DNA Replication video&review question

5 Famous Geneticists

Name: Edward B. Lewis
Birth: May 20, 1918 – July 21, 2004
Year of Fame: 1995 (Nobel Prize in Physiology or Medicine)

Contributions:  During the 1950s, Dr. Lewis studied the effects of radiation from X-rays, nuclear fallout and other sources as possible causes of cancer. His Nobel Prize winning studies with Drosophila, founded the field of developmental genetics and laid the groundwork for our current understanding of the universal, evolutionarily conserved strategies controlling animal development.

Publications: Lewis' key publications  in the fields of genetics, developmental biology, radiation and cancer are presented in the book Genes.

Name:Carolyn Widney "Carol" Greider

Birth: April 15, 1961-

Year of Fame:2009( Nobel Prize in Physiology or Medicine)

Contributions: Together with Elizabeth Blackburn and Jack W. Szostak, they discover  how chromosomes are protected by telomeres and the enzyme telomerase.

Publications: Blackburn and Greider  published their findings in the journal Cell in December, 1985.

Name:Barbara McClintock
Birth: June 16, 1902 – September 2, 1992
Year of Fame:1983(unshared Nobel Prize in Physiology or Medicine)

Contributions:McClintock studied chromosomes and how they change during reproduction in maize.  She developed the technique for visualizing maize chromosomes and used microscopic analysis to demonstrate many fundamental genetic ideas, including genetic recombination by crossing-over during meiosis—a mechanism by which chromosomes exchange information.

Publications:McClintock's key  publications are presented in the book: Genetics,Proceedings of the National Academy of Sciences, American Journal of Botany, and American Naturalist.  




 

Name: Arthur Kornberg

Birth: March 3, 1918 – October 26, 2007

Year of Fame: 1959(The Nobel Prize in Physiology or Medicine )

Contributions: Kornberg's primary research interests were in biochemistry, especially enzyme chemistry, deoxyribonucleic acid synthesis (DNA replication) and studying the nucleic acids which control heredity in animals, plants, bacteria and viruses. He discovery of "the mechanisms in the biological synthesis of deoxyribonucleic acid (DNA)" together with Dr. Severo Ochoa of New York University.

Publications: two Books,For the Love of Enzymes: The Odyssey of a Biochemist (1989) and The Golden Helix: Inside Biotech Ventures (2002)

Name: Hermann Joseph Muller

Birth: December 21, 1890 – April 5, 1967

Year of Fame: 1946(unshared Nobel Prize in Physiology or Medicine )

Contributions: Muller discovers the production of mutations by means of X-ray irradiation".

Publications: The Mechanism of Mendelian Heredity(1915)