Which of the following statements is/are correct? 1. DNA Polymerase uses a DNA template to catalyse the polymerisation of deoxynucleotides. 2. Adenosine triphosphate (ATP) are energy-carrying molecule found in the cells of all living things that captures chemical energy obtained from the breakdown of food molecules and releases it to fuel other cellular processes.
In living cells, such as E. coli, the process of replication requires a set of catalysts (enzymes). The main enzyme is referred to as DNA-dependent DNA polymerase since it uses a DNA template to catalyze the polymerization of deoxynucleotides. These enzymes are highly efficient as they have to catalyze the polymerization of a large number of nucleotides in a very short time. Hence statement 1 is correct. E. coli that has only 4.6×106 bp (compare it with a human whose diploid content is 6.6 × 109 bp ), completes the process ofreplication within 18 minutes; that means the average rate of polymerization has to be approximately 2000 bp per second. Not only do these polymerases have to be fast , but they also have to catalyze the reaction with a high degree of accuracy. Any mistake during replication would result in mutations. Deoxyribonucleoside triphosphates serve dual purposes. In addition to acting as substrates , they provide energy for polymerization reaction (the two terminal phosphates in deoxynucleoside triphosphates are high-energy phosphates , same as in the case of ATP ). Adenosine triphosphate (ATP) is an energy-carrying molecule found in the cells of all living things that captures chemical energy obtained from the breakdown of food molecules and releases it to fuel other cellular processes. Hence statement 2 is correct. In addition to DNA-dependent DNA polymerases, many additional enzymes are required to complete the process of replication with a high degree of accuracy. For long DNA molecules, since the two strands of DNA cannot be separated in their entire length (due to very high energy requirement), the replication occurs within a small opening of the DNA helix, referred to as replication fork. The DNA-dependent DNA polymerases catalyze polymerization only in one direction, that is 5'à 3'. This creates some additional complications at the replicating fork. Consequently, on one strand (the template with polarity 3'à 5' ), the replication is continuous , while on the other (the template with polarity 5'à 3' ), it is discontinuous . The discontinuously synthesized fragments are later joined by the enzyme DNA ligase.