DNA Replication

Roles of enzymes:

-Helicase: moves along a double-helical DNA, breaks the hydrogenbonds between two strands, unwinds the helix, and creates a replication fork.

-Single-stranded binding proteins: anneal to each single-stranded DNA immediately after it is unwinded by helicase to prevent it from reannealing.

-Gyrase: relieves the tension created by the unwinding of DNA at the replication fork by cutting the strands, letting them to rotate, and reconnecting them.

-Primase: builds short segments of RNA (primers), which are used by DNA polymerase III for elongation.

-DNA polymerase III: adds appropriate deoxyribonucleoside triphosphate to the 3' end of a parent strand, thereby creating a daughter strand in the direction of 5' carbon to 3' carbon. In each replication bubble, there is one leading strand and one lagging strand; the leading strand replicates towards the replication fork, the lagging strand replicates away from the fork. The leading strand is built continuously, whereas the lagging strand consists of many short segments of DNA called Okazaki fragments.

-DNA polymerase I: replaces the RNA primers in each Okazaki fragment and in the leading strand with corresponding DNA.

-DNA ligase: connects the Okazaki fragments by creating a phosphodiester bond.

-DNA polymerase I and DNA polymerase III also proofread the entire sequence, and fix any mistakes that were made in the replication process.

Here's a link that explains the replication process step-by-step.
A youtube video that gives an overview of the replication process.

Five Famous Geneticists

Thomas Hunt Morgan

(1866-1945)

Year of Fame: 1933

Publications that made him famous: "for his discoveries concerning the role played by the chromosome in heredity"

Contribution to the world of Genetics: Morgan was able to demonstrate that genes are carried on chromosomes and are the mechanical basis of heredity. These discoveries formed the basis of the modern science of genetics. He was the first person to be awarded the Nobel Prize in Physiology or Medicine for his work in genetics.

 Arthur Kornberg

(1918-2007)

Year of Fame: 1959

Publications that made him famous: "for [his] discovery of the mechanisms in the biological synthesis of ribonucleic acid and deoxyribonucleic acid"

Contribution to the world of Genetics: Arthur Kornberg spent decades isolating and purifying the enzymes that run the machinery of the cell. He and Severo Ochoa were the first to identify the enzyme catalyzing the synthesis of DNA, polymerase I.Kornberg's approach - isolating enzymes in the chemist's lab and analyzing them within their biological context - was a crucial component in understanding the molecular biology of the cell.

Marshal Warren Nirenberg

(1927-2010)

Year of Fame: 1968

Publications that made him famous: "for [his] interpretation of the genetic code and its function in protein synthesis"

Contribution to the world of Genetics: After a postdoctoral fellowship at the National Institutes of Health (NIH) in Bethesda, Maryland, he joined the staff as a research scientist. There he developed the procedure for deciphering the genetic code in living cells. He demonstrated that in protein production, each sequence of three chemical units—known as triplets or codons—in genetic material forms the arrangement for a specific amino acid. In 1961, he announced his discovery of the code for one amino acid. By 1966. Nirenberg had deciphered the code for the 20 amino acids involved in protein production.

Barbara McClintock

(1902-1992)

Year of fame: 1983

Publications that made her famous:"for her discovery of mobile genetic elements"

Contribution to the world of Genetics: McClintock studied chromosomes and how they change during reproduction in maize. Her work was groundbreaking: 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. She produced the first genetic map for maize, linking regions of the chromosome with physical traits, and demonstrated the role of the telomere and centromere, regions of the chromosome that are important in the conservation of genetic information.

 Werner Arber

(1929- )

Year of fame:1978

Publications that made him famous:"for the discovery of restriction enzymes and their application to problems of molecular genetics"

Contribution to the world of Genetics: He, Daniel Nathans,and Hamilton O. Smith together discovered restriction enzymes that break the giant molecules of DNA into pieces small enough to be separated for individual study, but large enough to retain meaningful amounts of the genetic information of the original substance. He also observed that bacteriophages cause mutation in their bacterial hosts and undergo hereditary mutations themselves.