031. During replication of DNA, which one of the following enzymes polymerizes the
1. DNA Polymerase I
2. DNA Polymerase II
3. DNA Polymerase III
4. RNA Polymerase I
Answer
1. DNA Polymerase III
Reference:
Harper 26th Edition Page 328
Lippincott 3rd Edition Page 403
Quality
Thinker and TRAP !!!
Status
Repeat, but with a slightly different stem
QTDF
Harper
Discussion
Before proceeding with the discussion, please read the question once again !!!! And now let us see what Harper says about DNA Polymerase
The polymerase III holoenzyme (the dnaE gene product in E.Coli) binds to template DNA as part of a multiprotein complex that consists of several polymerase accessory factors (beta, gamma, delta, delta’ and theta). DNA polymerases only synthesize DNA in the 5’ to 3’ direction and only one of the several different types of polymerases is involved at the replication fork. Because the DNA Strands are antiparallel, the polymerase functions asymmetrically. On the leading (Forward) strand, the DNA is synthesized continuously. On the lagging (retrograde) strand, the DNA is systhesized in short (1-5kb) fragments, the so called
Explanation
1. DNA Polymerase I (pol I) completes chain synthesis between Okasaki gragments on the lagging strand.
2. DNA Polymerase II (pol II) is mostly involved in proof reading and DNA repair
3. DNA Polymerase III synthesizes the leading strand as well as the Okasaki fragments.
4. RNA Polymerase I synthesizes synthesizes the precursor of the large ribosomal RNAs(28S, 18S and 5.8S) in the nucleolus.
Comments
The main confusion seems to because of a table given in Harper
E.Coli | Mammalian | Function |
I | a | Gap Filling and synthesis of lagging strand |
II | e | DNA Proofreading and repair |
| b | DNA repair |
| g | Mitochondrial DNA synthesis |
III | d | Processive leading strand synthesis |
Tips
Please note that synthesis of lagging strand involves DNA polymerase I, but the Okasaki fragments of the lagging strands are synthesized by DNA polymerase III
No comments:
Post a Comment