Enzyme function is critically important for the proper replication of DNA. Predi
ID: 100184 • Letter: E
Question
Enzyme function is critically important for the proper replication of DNA. Predict the consequence of a loss of function for each of the following enzymes:A) DNA gyrase B) DNA polymerase III C) DNA ligase D) DNA polymerase I Enzyme function is critically important for the proper replication of DNA. Predict the consequence of a loss of function for each of the following enzymes:
A) DNA gyrase B) DNA polymerase III C) DNA ligase D) DNA polymerase I
A) DNA gyrase B) DNA polymerase III C) DNA ligase D) DNA polymerase I
Explanation / Answer
A) Replication of DNA needs a number of enzymes. DNA gyrase is one of them. After the two strands are separated at the origin of replication, there is a tendency for the strands to coil up again. Imagine it in this way- you are separating two intertwined ropes at one point by pulling them apart with your hand. As soon as you remove your hand, the ropes will intertwine again. But if one end of partially separated ropes are cut, then the tension will be released and they will not coil up again. DNA gyrase do exactly the same thing. It makes a nick (cut) at one strand and reseals them, thereby releasing the tension. In its absence DNA helix will not be able to uncoil.
B) DNA polymerase III synthesizes a new DNA strand in 5' - 3' direction by joining free nucleotides complementary to the template strand in. If this enzyme is absent, DNA replication will not occur. Think of the consequence. There will be no cell division, no reproduction in lower organisms. The flow of life on this earth will come to a halt.
C) Against the 5' - 3' strand of DNA, a discontinuous strand is synthesized. Initially this new strand contains a number of RNA primers each joined with a small stretche of DNA segment called Okazaki fragment. DNA ligase joins these Okazaki fragments together by replacing the RNA primer with DNA. Lack of this enzyme will lead to synthesis of incomplete DNA strand.
D) DNA polymerase I performs the function of proof- reading after the new strand is synthesized. Sometimes a wrong base is introduced, though the frequency is one in ten thousand. DNA polymerase I removes the wrong base and replace it with the correct one. Proof- reading causes formation of identical DNA strands during replication. If there is any damage to DNA due to mutation, UV exposure etc. then after enzymatic removal (different enzyme) of the wrong nucleotides, DNA polymerase I synthesizes correct replacement using the intact strand as a template.
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