MCQsOnline - Online Collection of MCQs of Medical PG Entrance Exams.

MCQ stands for Multiple Choice Questions sometimes called as Objective type questions. Here we discuss the Old Question Papers, High Yield Points and Strategies with respect to the Indian Medical Post Graduate PG Entrance Exams like AIIMS,AIPG, JIPMER, CMC Vellore, PGI Chandigarh, UPSC, TNPSC, State PG Exams like Tamil Nadu PG (TN PG), Delhi PG, UPPG, Tamilnadu PG (TNPG), Karnataka PG, MAHE, COMED-K etc.

Target PG

PG Preparation

Related Portals

Search This Site

If you cannot locate what you want to find, please search using the box given below

Monday, December 15, 2008

Okasaki Fragments are seen during the synthesis of ds DNA

Question 31
Okasaki Fragments are seen during the synthesis of
a.       ds DNA
b.      ss DNA
c.       m RNA
d.      t RNA
Answer
a. ds DNA
Reference:
Harper 26th Edition Page 328, 27.335
Lippincott 3rd Edition Page 403
Quality
Thinker and TRAP !!!
Status
Repeat, but with a slightly different stem
QTDF
Harper
Discussion
An Okazaki fragment is a relatively short fragment of DNA (with an RNA primer at the 5' terminus) created on the lagging strand during DNA replication. It was originally discovered in 1968 by Reiji Okazaki, Tsuneko Okazaki, and their colleagues while studying replication of bacteriophage DNA in Escherichia coli.
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.
Explanation
When the lagging strand is being replicated on the original strand, the 5'-3' pattern must be used; thus a small discontinuity occurs and an Okazaki Fragment forms. On the lagging (retrograde) strand, the DNA is systhesized in short (1-5kb) fragments, the so called Okazaki fragments. These fragments are processed by the replication machinery to produce a continuous strand of DNA and hence a complete daughter DNA helix.
Comments
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
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
Reiji Okazaki  was a Japanese molecular biologist known for his research in DNA replication and especially for describing the role of so-called Okazaki fragments which he discovered working with his wife Tsuneko Okazaki in 1968.

No comments:

Post a Comment