Unit 2-2STUDENTS - Re w of Unit 2-1 vie plication-I NI TI...

Info iconThis preview shows pages 1–18. Sign up to view the full content.

View Full Document Right Arrow Icon
Review of Unit 2-1 DNA Replication-INITIATION Do old DNA strands pair with new or old DNA? Semiconservative Meselson and Stahl How and where does replication begin? Origin of replication Identification of Structure of Open Complex Prepriming complex
Background image of page 1

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

View Full Document Right Arrow Icon
Review of Unit 2-1 DNA Replication-INITIATION What proteins are required for DNA synthesis? Biochemical approach/protein fractions Kornberg Does replication go in one direction or bidirectionally? Polymerase reads the template strand from 3’ to 5’ New strand is synthesized from 5’ to 3’ Bidirectional replication Gyurasits and Wake Replicons
Background image of page 2
Today Unit 2-2 DNA Replication Complete initiation Elongation Termination
Background image of page 3

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

View Full Document Right Arrow Icon
Unit 2-2 DNA Replication-INITIATION
Background image of page 4
5' 3' 3' 5' oriC 5' 3' 5' 3' Once the Double Helix Is Opened at oriC, DNA Polymerases Can Begin to Make the New DNA (Daughter) Strands, BUT…. .. 5' 3' How is (+) supercoiling dealt with? Fork Fork
Background image of page 5

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

View Full Document Right Arrow Icon
Strand separation will place a physical strain on the helix – how to prevent? Replication goes at a rate of 500 – 750 nucleotides per second 10 bp per turn of the helix Must unwind at 50 - 75 turns per second ( 3000 RPM!! )
Background image of page 6
Unwinding of the helix by helicase during replication places strain on the DNA new old old A topoisomerase (DNA gyrase) relieves the strain
Background image of page 7

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

View Full Document Right Arrow Icon
Two Classes Of Topoisomerases Topoisomerase I Relaxes supercoils by nicking and re-sealing one strand of duplex DNA Topoisomerase II (includes DNA gyrase) Relaxes supercoils by nicking and re-sealing both strands of duplex DNA
Background image of page 8
How Can Replication Be Bidirectional if DNA Polymerases Work Only 5' to 3'? 5' 3' 3' 5' oriC 5' 3' 5' 3' Once the Double Helix Is Opened at oriC, DNA Polymerases Can Begin to Make the New DNA (Daughter) Strands, BUT…. .. 5' 3'
Background image of page 9

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

View Full Document Right Arrow Icon
Models for replication Fig. 20.6
Background image of page 10
These models were testable Small DNA fragments should be present
Background image of page 11

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

View Full Document Right Arrow Icon
Examined replication in T4 phage (replicating in E. coli). Pulse-experiment: treated cells with short pulse of 3 H thymidine. Isolated DNA in alkaline solution at different timepoints, estimated size by sucrose gradient. Okazaki’s experiment (1968) Seperation by mass (weight) Lighest Heaviest
Background image of page 12
Leading Lagging What do we expect if semi-discontinuous? At the early timepoint WHY?
Background image of page 13

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

View Full Document Right Arrow Icon
Leading Lagging What do we expect if semi-discontinuous? At the late timepoint WHY?
Background image of page 14
radioactivity Results show the presence of small fragments (1-2 kb). At early timepoints, only small fragments are present (2s), no long fragments! As time increased, the size of the labeled DNA fragments increases as the small fragments get “stitched” together Fig. 20.7
Background image of page 15

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

View Full Document Right Arrow Icon
What Primes DNA Replication? (remember that all DNA polymerases require a free 3’ OH) 5' 3' 3' 5' leading lagging 5' 3' 5' 3'
Background image of page 16
What Primes DNA Replication? A complex known as the "primosome" moves with the
Background image of page 17

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

View Full Document Right Arrow Icon
Image of page 18
This is the end of the preview. Sign up to access the rest of the document.

{[ snackBarMessage ]}

Page1 / 65

Unit 2-2STUDENTS - Re w of Unit 2-1 vie plication-I NI TI...

This preview shows document pages 1 - 18. Sign up to view the full document.

View Full Document Right Arrow Icon
Ask a homework question - tutors are online