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Dna replication
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- 2. Watson and Crick’smodel of replication • The base-pairing principal inherent for Watson-Crick model suggests that the two new strands are copied from two old strands.
- 3. Models of DNAreplication • Parent molecule remains the same • Completely new copy of the double helix is made • Parent strands separate and serve as templates for new strand synthesis • Hybrid molecules are made • New strands contain a mixture of old molecules and newly synthesized molecules
- 4. 1958: Matthew Meselson& Frank Stahl’s Experiment Equilibrium density gradient centrifugation
- 5. 1958: Matthew Meselson& Frank Stahl’s Experiment Semiconservative model of DNA replication
- 6. 1955: Arthur Kornberg Workedwith E. coli. Discovered the mechanisms of DNA synthesis. Four components are required: 1. dNTPs: dATP, dTTP, dGTP, dCTP (deoxyribonucleoside 5’-triphosphates) (sugar-base + 3 phosphates) 2. DNA template 3. DNA polymerase (Kornberg enzyme) 4. Mg 2+ (optimizes DNA polymerase activity) 1959: Arthur Kornberg (Stanford University)
- 7. DNA polymerase • DNApolymerases are important enzymes involved in DNA • replication. • Three polymerases have been purified from E.coli. • In addition to important role in filling the gaps between • Okazaki fragments, DNA polymerase I is the most important enzyme for gap filling during DNA repair. • DNA polymerase II functions in gap filling and appears to facilitate DNA synthesis directed by damaged templates. • DNA polymerase III catalyzes chain elongation at the • growing fork of E. coli.
- 8. Three main featuresof the DNA synthesis reaction: 1. DNA polymerase I catalyzes formation of phosphodiester bond between 3’-OH of the deoxyribose (on the last nucleotide) and the 5’-phosphate of the dNTP. • Energy for this reaction is derived from the release of two of the three phosphates of the dNTP. 2. DNA polymerase “finds” the correct complementary dNTP at each step in the lengthening process. • rate ≤ 800 dNTPs/second • low error rate 3. Direction of synthesis is 5’ to 3’ DNA polymerase Image credit: Protein Data Bank
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- 10. There are manydifferent types of DNA polymerase Polymerase Polymerization (5’-3’) Exonuclease (3’-5’) Exonuclease (5’-3’) #Copies I Yes Yes Yes 400 II Yes Yes No ? III Yes Yes No 10-20 •3’ to 5’ exonuclease activity = ability to remove nucleotides from the 3’ end of the chain •Important proofreading ability •Without proofreading error rate (mutation rate) is 1 x 10-6 •With proofreading error rate is 1 x 10-9 (1000-fold decrease) •5’ to 3’ exonuclease activity functions in DNA replication & repair.
- 15. Number of replicationorigins Prokaryotes • 1 replication origin per chromosome • replication rate = 500 nucleotides per sec. Eukaryotes • multiple replication sites on each chromosome. • replication rate = 50 nucleotides per sec.
- 16. DNA Replication Originof E.coli • E. coli replication origin oriC is an ≈240bp DNA segment present at the start • site for the replication of the E. coli chromosomal DNA. • Plasmids or any other circular DNAs containing oriC are capable of independent and controlled replication in E. coli cells. • DnaA protein initiates replication. • In addition, the E. coli genome contains a segment of DNA with a relatively high A+T content adjacent to the oriC.
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- 20. • DNA polymeraseis discovered by A. Watson and Crick B. Crickmore C. Meselson & Stahl’s D. Korenberg •
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- 22. • DNA polymeraseis discovered in a. 1954 b. 1955 c. 1958 d. 1962
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- 24. 1.Semi conservative replicationof DNA was first demonstrated in a.Drosophila melanogaster b.E. Coli c.Arabidopsis thaliana d.Human
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- 26. 1.Mode of DNAreplication in E. Coli is a.Conservative and unidirectional b.Semi conservative and unidirectional c.Conservative and bidirectional d.Semi conservative and bidirectional
- 27. • Semi conservativeand bidirectional
- 28. 1.When DNA replicationstarts a.The phosphodiester bond between adjacent nucleotides breaks b.The bond between nitrogen base and deoxyribose breaks c. The hydrogen bond between the nucleotides of two strand breaks d.The leading strand produces okazaki fragment
- 29. • The hydrogenbond between the nucleotides of two strand breaks
- 30. • Which ofthe following enzyme require ATP or NAD for reaction a.DNA ligase b.DNA polymerase c.DNA gyrase d.Endonucleases
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- 32. 1.During the replicationof DNA, the synthesis of DNA on lagging strand takes place in segment, these segments are called a.Satellite segment b.Okazaki segment c.Kornberg segment d.Double helix segment
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- 34. 1.True replication ofDNA takes place due to a.Complementary base pairing rule b.Hydrogen bonding c.Phosphodiester bonding d.Transcription and translation
- 35. • Complementary basepairing rule
- 36. 1.Unwinding of DNAIs done by a.Topoisomerase b.DNA polymerase c.Helicase d.Ligase
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- 38. 1.DNA replication isspecifically measured by estimating the incorporation of radio labelled a.Adenine b.Uracil c.Cytosine d.Thymine
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- 40. 1.The elongation ofleading strand during DNA synthesis a.Progresses away from replication fork b.Occurs in 3’ – 5’ direction c.Depend on the action of DNA polymerase d.Produces okazaki fragments
- 41. • Depend onthe action of DNA polymerase
- 42. 1.Which of thefollowing is not needed for DNA replication? a. Ribosomes b. DNA c. Nucleotides d. Enzymes
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- 44. • Experimental prooffor semiconservative mode of replication is give by A. Watson and Crick B. Meselson & Stahl’s C. Korenberg D. Khurana
- 45. • Meselson &Stahl’s
- 46. • Idea ofDNA replication firstly proposed by A. Watson and Crick B. Crickmore C. Meselson & Stahl’s D. Korenberg
- 47. • Watson andCrick
- 48. • Rate ofDNA replication is a. Faster in prokaryotes than Eukaryotes b. Faster in Eukaryotes than prokaryotes c. Same in both Eukaryotes & prokaryotes d. None of these
- 49. • Faster inprokaryotes than Eukaryotes
- 50. • Which ofthe following is E. coli origin of replication a. oriA b. oriB c. oriC d. oriD
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- 52. • Which ofthe following is origin of replication of yeast a. Ori C b. ARS c. ARU d. Ori A
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- 54. • Which ofthe following protein initiates DNA replication in E.coli a. DnaA b. DnaB c. SSB d. SSA
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- 56. • DNA polymeraseis also known as a. Kornberg's Enzyme b. RNA polymerase c. dNTPs adding and removing enzyme d. PCR enzyme
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- 58. 1.Which of thefollowing enzyme is used for joining of bits of DNA? a.DNA ligase b.DNA polymerase c.DNA gyrase d.Endonucleases
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- 60. • Which ofthe following enzyme plays important role in gap filling DNA repair mechanism a. DNA polymerase I b. DNA polymerase II c. DNA polymerase III d. RNA polymerase I
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