Question

A gene encoding one of the proteins involved in the DNA replication has been inactivated by a mutatiion in a cell. In the absence of this protein the cell attempts to replicate its DNA for the very last time. What DNA products would be generated in each case if the following protein were missing / mutated? (a) primase(b) DNA ligase(c) DNA polymerase I

Answer 1

Answer:

primase - unwinded parental double helix DNA, no replication.

DNA ligase - new double helix DNA, one old strand and okazaki fragments

DNA polymerase 1 - original DNA strands, daughter strands with primers still attached.

Explanation:

The primase enzyme is responsible for the synthesis of RNA primer which binds with unwinded DNA strands at the origin of replications and serves as a starting chain for the daughter strands. Hence, their absence during replication will lead to the discontinuation of the replication process after the unwinding of the double helix structure by the helicase enzyme.

DNA ligase functions as to join fragments of DNA synthesized discontinuously (okazaki fragments) during replication. Okazaki fragments are generated after replication of the leading and the lagging strands have been complete. Hence, the absence of the DNA ligase will result in the lagging strands existing as a lone strand along with the okazaki fragments and a newly replicated DNA consisting of one old leading strand and its newly synthesized complimentary strand.

The DNA polymerase 1 is responsible for the removal of RNA primers and replacing them with DNA nucleotides after the elongation process. Hence, the absence of the enzyme will cause incomplete replication process.