Lecture 4 DNA Replication, Repair, and Recombination

Lecture 4 DNA Replication, Repair, and Recombination -...

Info icon This preview shows pages 1–11. Sign up to view the full content.

View Full Document Right Arrow Icon
Chapter 28 DNA Replication, Repair, and  Recombination  
Image of page 1

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full Document Right Arrow Icon
DNA replication, damage, and repair DNA structure; DNA modifying enzymes
Image of page 2
DNA replication Reaction direction complementary Semi-conservative required 5’ 3’
Image of page 3

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full Document Right Arrow Icon
Steps of DNA replication
Image of page 4
Klenow fragment  DNA polymerase I lacking 5’ end  First DNA polymerase identified DNA polymerase I 5’-3’exonuclease 3’-5’exonuclease Core polymerase Kleno w
Image of page 5

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full Document Right Arrow Icon
DNA polymerases   Two  metal ions (typically Mg 2+ ) participate  in the polymerase reaction (interact with  primer  and  dNTP )  Specificity of replication is dictated by  complementarity of shape between bases
Image of page 6
E. coli chromosomal replication  Replication structures can be seen by electron microscopy Theta structures Replication forks  Replication  starts at a unique site  (~245 bp) on the  E. coli  chromosome –  Ori C  Two replication forks progress around the chromosome in opposite directions  The two replication forks meet at a unique location (tre) and replication ends
Image of page 7

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full Document Right Arrow Icon
DNA replication : 5~6 nucleotides OH RNA (primer)removed (exonuclease)/DNA filled by DNA  polymerase I Ligated by DNA ligase = RNA polymerase  (DnaG) (RNA pol does not need primer) III (New DNA)
Image of page 8
Leading strand and lagging strand (Okazaki fragments) DNA polymerases catalyze synthesis of DNA strand in 5’ to 3’ direction  – but replication forks  appear to be synthesizing one strand in 5’ to 3’ direction and the other strand in 3’ to 5’ direction. •  Problem was solved by Okazaki who showed that one strand is synthesized continuously  (leading strand) and the other strand is synthesized  discontinuously  (lagging strand) . •  Discontinuous synthesis leads to production of DNA fragments of 500-1000bp known as  Okazaki fragments . •   DNA Polymerase III  synthesizes both  the leading strand and lagging strand. It is a highly  processive enzyme and incorporates many thousands of nucleotides before letting go of DNA. 5’ 5’ 3’ 3’ 3’ 5’ Theta structure Replication fork Replication fork
Image of page 9

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full Document Right Arrow Icon
Lagging strand synthesis • Lagging strand synthesis involves synthesis of short RNA primers by the RNA polymerase called  primase. DNA polymerase III then elongates these RNA primers to generate Okazaki fragments. • RNA is removed ( 5’ to 3’ exonuclease  activity) and gaps between Okazaki fragments are filled by  DNA polymerase I. • Finally, the DNA fragments on the lagging strand are joined by DNA ligase .
Image of page 10
Image of page 11
This is the end of the preview. Sign up to access the rest of the document.

{[ snackBarMessage ]}

What students are saying

  • Left Quote Icon

    As a current student on this bumpy collegiate pathway, I stumbled upon Course Hero, where I can find study resources for nearly all my courses, get online help from tutors 24/7, and even share my old projects, papers, and lecture notes with other students.

    Student Picture

    Kiran Temple University Fox School of Business ‘17, Course Hero Intern

  • Left Quote Icon

    I cannot even describe how much Course Hero helped me this summer. It’s truly become something I can always rely on and help me. In the end, I was not only able to survive summer classes, but I was able to thrive thanks to Course Hero.

    Student Picture

    Dana University of Pennsylvania ‘17, Course Hero Intern

  • Left Quote Icon

    The ability to access any university’s resources through Course Hero proved invaluable in my case. I was behind on Tulane coursework and actually used UCLA’s materials to help me move forward and get everything together on time.

    Student Picture

    Jill Tulane University ‘16, Course Hero Intern