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DNA replica process

Bio 2 Lecture 13

QuestionAnswer
Give an overview of DNA replication -2 strands are separated -Occurs in 2 opposing directions from the origin -Each strand of the OG DNA molecule serves as a template to build the new strands (semiconservative) -New helix will be composed of an OG DNA strand & a newly synthesized strand
What are the 3 phases of DNA replication? 1) Initiation (formation of the replisome) 2) Elongation (Addition of nucleotides to make new strands of DNA) 3) Termination (Completion of DNA synthesis)
How is DNA replication for prokaryotes? 1) One circular chromosome is replicated 2) Has only one point of origin of replication 3) Takes place in the cell cytoplasm 4) Takes 1 hr and occurs continuously 5) Replication is bidirectional
How is DNA replication for eukaryotes? 1) 24 hrs to copy 2) Many linear chromosomes replicated 3) Many points of origin of replication 4) In the nucleus 5) Only undergo DNA replication during S-phase of the cell cycle
What are the similarities between eukaryotic and prokaryotic replication? 1) Occur before mitosis 2) DNA is double stranded 3) Replication occurs in 5' to 3' direction on new strand 4) Single-Strand binding proteins (SSBP) stabilize ssDNA 5) RNA primer is synthesized by primase 6) Bidirectional
What is the function of DNA Gyrase? Stabilizes DNA helix as it is unwound by Helicase
What is the function of Single Stranded Binding Protein? Hold unzipped, single-stranded sections of DNA apart during replication
What is the function of helicase? Unwinds DNA helix and unzips strands by breaking H-bonds
What is the function of DNA polymerase III? Adds new DNA nucleotide in the 5' to 3' direction
What is the function of DNA primase? Adds primers of RNA nucleotides to the laggins strand as starting points for replication
What is the function of DNA polymerase I? Replaces RNA primers with DNa nucleotides
What is the function of DNA ligase? Joins Okazaki fragments on lagging strands
What are the 2 restrictions of DNA polymerase III? 1) Can only add nucleotides to the 3' end of an existing nucleotide (the reason for RNA primer) 2) Can only add nucleotides to the 3' -OH end of a nucleotide
Why does DNA polymerase III ass DNA nucleotides? To elongate DNA
DNA replication must be... semi-discontinuous
What is the replication of the leading strand? Continuous replication, so in the same direction the fork opens since 3' -OH is always exposed
What is the synthese of the lagging strand? Synthesized discontinuously, creating Okazaki fragments (for the 3'-OH end to be exposed, the replication fork must open up considerably to expose adequate length of DNA to place a primer)
Why is DNA replication semi-continuous? Since the two strands of DNA have opposite polarities, DNA synthesis can not proceed on both strands, utilizing same enzyme, unless the synthesis proceeds in pieces.
What is the problem of copying ends on lagging strand? Problem synthesizing the ends of the lagging strand because it runs out of room to place primer on the 5’ end. With each round of DNA replication, the linear eukaryotic chromosome would become shorter.
What prevents the shortening of chromosomes? What is it produced by? Telomerase produced by telomerase enzyme
What does telomerase have that allows DNA to be added to the end of the lagging strand? Because it contains its own RNA region that is used as a template
What are telomeres? Repeated DNA sequence on the ends of eukaryotic chromosome
What do we cal chemical or physical agents that can damage DNA? examples Mutagens. Ex: Sun's radiation
What are the 2 DNA repair mechanisms? 1) Specific (targeting a particular type of DNA damage, like) 2) Non-specific (able to repair many different kinds of DNA damage)
What is excision repair? To correct damaged or mismatched nitregenous bases. It's non-specific
Example of specific repair Photo-repair of thymine dimers
Created by: Malayka
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