DNA replication In molecular biology, DNA replication is the biological process of producing two identical replicas of DNA from one original DNA molecule. - презентация

1 DNA replication In molecular biology, DNA replication is the biological process of producing two identical replicas of DNA from one original DNA molecule. DNA is duplicated by replication, in which the two strands of a parental DNA molecule unwind and each serves as a template for the synthesis of a complementary copy. DNA is duplicated by Semiconservative replication, in which the two strands of a parental DNA molecule unwind and each serves as a template for the synthesis of a complementary copy.

2 Semiconservative replication original new Semiconservative replication would produce two copies that each contained one of the original strands and one new strand. The mechanism of replication was one of three models originally proposed for DNA: semiconservative, conservative, dispersive.

3 Conservative replication two new strands Conservative replication would leave the two original template DNA strands together in a double helix and would produce a copy composed of two new strands containing all of the new DNA base pairs. In the conservative replication model, the two strands of the original molecule serve as templates for the two strands of a new DNA molecule, then rewind into an all "old" molecule After the two complementary copies separate from their tem­plates, they wind together into an all "new" molecule.

4 Dispersive replication Dispersive replication would produce two copies of the DNA, both containing distinct regions of DNA composed of either both original strands or both new strands. In the dispersive replication model, neither parental strand is con­ served and both chains of each replicated molecule contain old and new segments

5 only this process have biological significance The model of replication Watson and Crick proposed is termed semiconservative replication. Other sci­entists proposed two other models for replication.

6 The key molecular events of DNA replication are as follows 1. The two strands of the DNA molecule unwind for replication to occur helicase Before replication can take place, an enzyme called helicase unwinds the DNA molecule from its tightly woven form. This opens up or unzips the double- stranded DNA to give two single strands of DNA that can be used as templates for replication.

7 In a cell, DNA replication begins at specific locations, or origins of replication. replication forks Unwinding of DNA at the origin and synthesis of new strands results in replication forks growing bi- directionally from the origin.

8 2. DNA polymerase adds nucleotides to an existing chain. DNA polymerases are enzymes that synthesize DNA molecules from deoxyribonucleotides, the building blocks of DNA. These enzymes are essential to DNA replication and usually work in pairs to create two identical DNA strands from a single original DNA molecule. During this process, DNA polymerase reads the existing DNA strands to create two new strands that match the existing ones.

9 3. DNA polymerase moves along the old strand in the 3'-5' direction, creating a new strand having a 5'-3' direction. The overall direction of new synthesis is in 5 to 3 direcion, which is a direcion antiparalled to that of the template strand

10 Nucleotides enter into a newly synthesized chain according to the A-T and G-C complementary base- pairing rules.

11 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.