REPLICATION OF DNA
One of the most important properties of DNA is that it can make exact copies of itself. This process is called replication. The two stands of DNA double helix are united by hydrogen bonds between the purine and pyrimidine base pairs. When the hydrogen bonds break the two strands separate and unwind. The nucleus contains free nucleotides, which form the nucleotide pool. These free nucleotides pair with the nucleotides of the two separated strands by means of hydrogen bonds. Free adenine nucleotide pairs with thymine nucleotide of the strand and free guanine nucleotide pairs with the cytosine nucleotide of the strand, etc. In this way a new strand is formed around each of the old strand. The result of replication is the formation of tow double helices, each identical to the original.
One of the most important properties of DNA is that it can make exact copies of itself. This process is called replication. The two stands of DNA double helix are united by hydrogen bonds between the purine and pyrimidine base pairs. When the hydrogen bonds break the two strands separate and unwind. The nucleus contains free nucleotides, which form the nucleotide pool. These free nucleotides pair with the nucleotides of the two separated strands by means of hydrogen bonds. Free adenine nucleotide pairs with thymine nucleotide of the strand and free guanine nucleotide pairs with the cytosine nucleotide of the strand, etc. In this way a new strand is formed around each of the old strand. The result of replication is the formation of tow double helices, each identical to the original.
Replication:
1. Replication takes place during the interphase between two mitotic cycles.
2. Replication is semi-conservative process in which each of the two double helices formed from the parent double strand have one old and one new strand. Repair replication is non-conservative.
3. DNA replication requires a DNA template, a primer, deoxyribonucleoside triphosphates (dATP, dGTP, dTTP and dCTP), Magnesium ions, DNA unwinding protein, superhelix relaxing protein, a modified RNA polymerase to synthesize RNA primer, the products of dnaA, dnaB, dnaC-D, dnaE and dnaG genes and polynucleotide ligase, a joining enzyme.
4. Replication starts at a specific point called the origin.
5. According to one model replication starts with a ‘nick’ or incision made by an incision enzyme (endonuclease).
6. The two strands of the DNA double helix unwind with the help of a DNA unwinding protein (also called the DNA binding protein) which binds to single DNA strands.
7. The unwinding of the strands imposes strain, which is relieved by the action of a superhelix relaxing protein.
8. Initiation of DNA synthesis requires an RNA primer. The primer is synthesized by the DNA template close to the origin of replication. A special form of RNA polymerase catalyzes the synthesis.
9. Deoxyribose nucleotides are now added to the 3’ end of the RNA primer and the main DNA stand is synthesized on the DNA template. This strand is complementary to the DNA strand and is synthesized by DNA polymerase III.
10. The enzyme DNA Polymerase I now degrades the RNA primer and simultaneously catalyses the synthesis of a short DNA segment to replace the primer. This segment is then joined to the main DNA strand by a DNA ligase.
11. Replication takes place discontinuously and short pieces called Okazaki fragments are synthesized. One strand may synthesize a continuous strand and the other Okazaki fragments, or both strands may synthesize Okazaki fragments. Thus one strand is synthesized forwards and the other backwards.
12. The Okazaki pieces are joined by polynucleotide ligase, a joining enzyme, to form continuous strands.
13. Replication may be in one direction (unidirectional) from the point of origin or in both directions (bidirectional).
1. Replication takes place during the interphase between two mitotic cycles.
2. Replication is semi-conservative process in which each of the two double helices formed from the parent double strand have one old and one new strand. Repair replication is non-conservative.
3. DNA replication requires a DNA template, a primer, deoxyribonucleoside triphosphates (dATP, dGTP, dTTP and dCTP), Magnesium ions, DNA unwinding protein, superhelix relaxing protein, a modified RNA polymerase to synthesize RNA primer, the products of dnaA, dnaB, dnaC-D, dnaE and dnaG genes and polynucleotide ligase, a joining enzyme.
4. Replication starts at a specific point called the origin.
5. According to one model replication starts with a ‘nick’ or incision made by an incision enzyme (endonuclease).
6. The two strands of the DNA double helix unwind with the help of a DNA unwinding protein (also called the DNA binding protein) which binds to single DNA strands.
7. The unwinding of the strands imposes strain, which is relieved by the action of a superhelix relaxing protein.
8. Initiation of DNA synthesis requires an RNA primer. The primer is synthesized by the DNA template close to the origin of replication. A special form of RNA polymerase catalyzes the synthesis.
9. Deoxyribose nucleotides are now added to the 3’ end of the RNA primer and the main DNA stand is synthesized on the DNA template. This strand is complementary to the DNA strand and is synthesized by DNA polymerase III.
10. The enzyme DNA Polymerase I now degrades the RNA primer and simultaneously catalyses the synthesis of a short DNA segment to replace the primer. This segment is then joined to the main DNA strand by a DNA ligase.
11. Replication takes place discontinuously and short pieces called Okazaki fragments are synthesized. One strand may synthesize a continuous strand and the other Okazaki fragments, or both strands may synthesize Okazaki fragments. Thus one strand is synthesized forwards and the other backwards.
12. The Okazaki pieces are joined by polynucleotide ligase, a joining enzyme, to form continuous strands.
13. Replication may be in one direction (unidirectional) from the point of origin or in both directions (bidirectional).
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