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HIGH YIELD TERMS For AIIMS, AFMC, AIPMT, JIPMER 1.DNA REPLICATION 1. Heterocyclic function of DNA When DNA directs the synthesis of molecules other itself. Egs. Protein synthesis, DNA synthesis. 2. Autocatalytic function When DNA directs the synthesis of DNA itself. 3. Conservative replication A new DNA is formed over the template of old structure. 4. Semi conservative replication In each replica, one strand is old and the other new. 5. Disruptive replication Old DNA undergoes fragmentation. 6. Mathew Messelson and Franklin Stahl – 1958 Conducted experiments In E.coli DNA to study Semi conservative replication. 7. J. H. Taylor and P. Woods – 1957 Proved that Eukaryotes also shows semi conservative DNA replication. They conducted experiments in Vicia faba ( bean ). 8. Kornberg – 1956 Succeeded in demonstrating the synthesis on DNA in test tube. He extracted an enzyme from bacterium E.coli that was capable of linking free DNA molecules. He named the enzyme as DNA polymerase. 9. DNA polymerases Enzyme for DNA synthesis. Three forms of DNA polymerases are found in prokaryotes. DNA polymerase I – DNA repairing enzyme. DNA polymerase II – DNA repairing enzyme. DNA polymerse III – DNA replicating enzyme. 10. Kornberg Enzyme DNA polymerase I is called as Kornberg enzyme. It is the actual DNA repairing enzyme. 11. Eukaryotic DNA polymerases 5 types are present. DNA polymerase Alpha, Beta Gamma, Delta, and Epsilon. 12. Zipper duplication Sequential opening of DNA duplex and its replicati on to form two DNA strands . 13. Origin of replication – Ori. Starting point of DNA replication. It usually contai ns sequences rich in weak A-T base pairs .Only double bonds are present between A – T. 14. Helicase Enzyme that unwinds DNA strands. 15. Topoisomerases Enzyme that reduce the tension during DNA unwinding. 16. DNA gyrases In prokaryotes, the DNA polymerases and topoiso merases are replaced by Gyrases. 17. SSB proteins Single Stranded Proteins – stabilize the separated DNA strands. 18. Primase RNA polymerase is called Primase. It helps DNA polymerse to start DNA synthesis. 19. RNA primer Short strand of RNA synthesized to start DNA syn thesis. 20 DNA polymerase III establish phospho diester bonds between nucleotides. 21.Leading strand DNA strand in which continuous synthesis occurs in the 5’ – 3’ direction. Replication is continuous. 22. Lagging strand the second strand in which DNA synthesis occurs by producing segments of DNA. 23. Okasaki fragments named by R.Okasaki. The short DNA fragments synthesi sed in the lagging strand. Okasaki fragments are formed because DNA polymerase can act only in the 5’-3’ direction The replication is thus discontinuous. It contains 1000 1500 nucleotides. 25. DNA ligase Enzyme that joins DNA segments. Discovered by Khorana. MCQs based on DNA replication 1. DNA polymerase is required for the synthesis of a. DNA from DNA b. RNA from RNA c. RNA from DNA d. DNA from RNA 2. origin of replication is a. one in all organisms b. one in prokaryotes and many in eukaryotes c. one in eukaryotes and many in prokaryotes d. several in all. 3. Okasaki segments are small pieces of DNA containing 1000 to 1500 nucleotides and are formed in a. lagging strand b. leading strand c. sense strand d. non sense strand 4. The area of unwinding and separation of DNA strands during replication is called a. origin b. initiation point c. primer d. replication fork 5. In DNA replication, the primer is a. small deoxy ribonucleotide polymer b. small ribo nucleotide polymer c. helix destabilizing protein d. enzyme taking part in joining nucleotides to their complementary template bases 6. Topoisomerase is involved in a. producing RNA primer b. joining DNA segments c. producing nick in DNA d. separation of DNA strands 7. DNA strand is synthesized in the direction a. 5’-3’ b. 3’-5’ c. 1’-3’ d. 6’-1’ 8. Okasaki fragments are joined by a. DNA polymerase III b. DNA ligase c. DNA polymerse II d. DNA polymerse I 9. Leading strand during DNA replication is formed a. continuously b. in short segments c. first d. ahead of replication 10. In proof reading during DNA replication a. wrong nucleotides are inserted b. wrong nucleotides are taken out c. wrong nucleotides are removed and correct ones are inserted d. mutations are prevented 11. E.coli fully labeled with N15 is allowed to grow in N14 medium. The two strands of DNA molecule of the first generation bacteria have a. different density and do not resemble parent DNA b. different density but resemble parent DNA c. same density and resemble parent DNA d. same density but do not resemble parent DNA CBSE 1992 12. DNA having labeled thymidine is allowed to replicate in medium having nonradioactive thymidine. After three duplication, the DNA molecules having labeled thymidine shall be a. one molecule b. two molecules c. four molecules d. eight molecules AIIMS 1993 13. DNA replication is a. conservation and discontinuous b. semi conservative and semi discontinuous c. semi conservative and discontinuous d. conservative AIPMT 1999 14. In vitro synthesis of RNA and DNA was carried out first by a. Kornberg and Nirenberg b. Ochoa and Kornberg c. Ochoa and Nirenberg d. Nirenberg and Khorana BHU 1996 15. Semi conservative DNA / chromosome replication using N15 was demonstrated by a. Messelson b. Taylor c. Messelson and Stahl d. Hershey and Chase AIIMS 1994 16. DNA replication requires a. DNA polymerase only b. RNA polymerase and translocase c. DNA ligase only d. DNA polymerse and DNA ligase CPMT 1994 17. Ligase is an enzyme required for a. breaking DNA b. joining DNA bits c. renaturation of DNA d. proof reading AIIMS 1994 18. The one which is capable of self replication is a. DNA b. RNA c. Enzyme d. Protein CPMT 1998 19. DNA duplication or multiplication is known as a. replication b. transcription c. transduction d. translation 20. DNA replication in eukaryotes commences a. from both ends of chromosomes simultaneously b. several sites along DNA of a chromosomesimultaneously c. from centromere to either ends d. from one end of the chromosome to the other ANSWER KEY CPMY 1998 BHU 2001 DNA replication 1. a 2.b 3.a 4.a 5.b 6.c 7.a 8.b 9.a 10.c 11.a 12.b 13.b 14.b 15.c 16.d 17.b 18.a 19.a 20.b