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Penn State - MICRB 251 - Class Notes - Microbiology 251: Chapter 5

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Penn State - MICRB 251 - Class Notes - Microbiology 251: Chapter 5

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background image Microbiology 251 
Chapter 5: DNA Replication, Repair, and Recombination
Lectures 1,2
Lecture 1: DNA Synthesis and Machinery -riboses are attached by a phosphate that bridges 3’ and 5’ carbons
-nucleotides are always added from 5’ to 3’
-can only be added to the 3’ end -DNA polymerase builds in a 5’ to 3’ direction -requires primer to begin
-occasionally adds wrong nucleotide
-1 mistake per 100,000 nucleotides -doesn’t correct incorrect nucleotide itself -marks incorrect base
-another enzyme is responsible for the correction
-DNA primase -makes short RNA primers that provide the 3’ OH for DNA  polymerase to start synthesis
-Okazaki fragment:
RNA primer + nucleotides
-connecting fragments involves degrading RNA primer and 
ligating the nick
-RNase H degrades RNA in the heteroduplexed region
-DNA polymerase fills gap (from degraded primers)
-DNA ligase ligates the nick
-ATP used
-AMP released
-DNA helicase -can mechanically separate 2 DNA strands -uses ATP -Single Stranded DNA Binding Protein (SSB) -prevents hairpins from forming in single stranded DNA -even though bases are on same strand, they can still bind  with the correct opposite base if not prohibited from doing so
-sliding clamp protein
-regulates association of DNA polymerases with template
-placed on DNA by clamp loader
-ATP binding opens sliding clamp so DNA can engage
-ADP + P released
-when DNA polymerase unwinds DNA at the fork, the DNA ahead of the
fork overwinds
-produces stress in DNA
background image -topoisomerases (topo’s) -untangles DNA by introducing transient breaks in DNA -topo 1 -1 strand
-cuts 1 spot
-forms covalent bond with DNA backbone
-no ATP needed
-topo 2 -2 strand
-needs ATP
-makes reversible covalent attachment to opposite DNA strands
-both topo’s hold onto DNA so it doesn’t float away and is lost
-strand directed mismatch repair:
-MutS - finds mismatches -MutL -detects nick in new DNA strand -able to tell which strand is newly synthesized -can accurately remove and replace Lecture 2: DNA Replication in Cells -in E. coli: -replication origin is AT rich and associates with initiator proteins -recruit DNA helicase
-AT forms 2 H bonds
-easier to pull apart than 3 between C and G -eukaryotic chromosomes have more than 1 origin of replication -if eukaryotes had 1, chromosome replication would take a  month -some origins are more frequently used than others -some origins are weaker and are used as back ups -each origin of replication has 2 forks with each having a leading and 
lagging strand
-forks merge to form whole chromosome -firing of replication origins regulated by cell cycle
-origin recognition complex (ORC) serves as initiator proteins in 
-bonded to DNA at all times -only activated by kinase to transition into S-phase -recruits a DNA helicase -also activated by kinase -once origin has fired, ORC remains inactive until cell divides
-cell doubles amount of histones produced

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School: Pennsylvania State University
Department: Microbiology
Course: Molecular and Cell Biology I
Professor: Scott Lindner
Term: Fall 2016
Tags: Microbiology, DNA, and replication
Name: Microbiology 251: Chapter 5, Lectures 1 and 2 Notes
Description: These notes are from chapter 5 lectures 1 and 2 which were on 9/14 and 9/16. They cover DNA replication and repair.
Uploaded: 09/19/2016
3 Pages 19 Views 15 Unlocks
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