Unformatted text preview: BIO 106 Fall 2009 Professor Owen 10/14/2009 DNA Replication DNA Repair PCR In the DNA of certain isolated cells, 13% of the nucleotides are adenine. What are the percentages of the other nucleotides? 13% G, 37% T, 37% C B. 13% G, 13% T, 13% C C. 13% T, 37% G, 37% C D. 13% T, 13% G, 48% C
A. Cooper 6.13 A Problem …
Since the two strands of DNA run in opposite directions, continuous synthesis of two new strands at the replication fork would require that one strand be synthesized in the (wrong) 5’ to 3’ direction. eukaryotic bacterial Origin of Replication
Replication initiates at multiple origins (ori). Each origin produces two replication forks.
Cooper 6.12 The Replication Forks Are Asymmetric Replication Fork is Asymmetrical
Since DNA polymerase only works in the 5’ to 3’ direction direction, it must grow discontinuously in in separate small pieces with the enzyme working backwards from the replication fork. These pieces are called Okazaki fragments.
ECB3 6-12 Leading-strand Lagging-strand 16 DNA Replication II & PCR 1 BIO 106 Fall 2009 Professor Owen 10/14/2009 Okazaki Fragments Cooper 6.3 DNA Polymerase is Self-correcting SelfDNA polymerase proofreads its own work. The final product is accurate to only one error in 107 nucleotides. 10 The leading strand is continuously synthesized in the direction of the replication fork movement. The lagging strand is formed in small pieces (Okazaki fragments) backward from the overall direction of replication, then joined together. ECB3 6-13 Proofreading Explains 5’ 3’ Direction of DNA Synthesis Only addition in 5’ to 3’ gives to gives the the correct end for adding the next base. Starting Replication: RNA Primers ? DNApolymerase DNA polymerase can only add polymerase can only add nucleotides to an existing nucleotide chain, it cannot start a completely new DNA strand. ECB3 6-15 Cooper 6.4 RNA Primers
Which of the following would you guess is the enzyme that synthesizes the RNA primers? primase B. helicase C. DNA polymerase D. RNAase E. splicease
Cooper 6.4 16 DNA Replication II & PCR 2 BIO 106 Fall 2009 Professor Owen 10/14/2009 Removal of RNA Primers
Cooper 6.5 Helicase
What opens the DNA molecule so this process can occur? Th The enzyme helicase unwind the strands of DNA ahead of the replication fork. enzyme is DNA ligase Cooper 6.8 Proteins at Replication Fork
How does the DNA polymerase enzyme attach and move along the DNA? A “sliding clamp” protein complex helps this process. What is the function of the helicase enzyme? wrap the DNA into an -helix B. unwind the DNA C. add new nucelotides D. make RNA primers
A. Replication Fork – More Accurate
How does the DNA polymerase enzyme attach and move along the DNA? A “sliding clamp” protein complex helps this process.
movie 6.5 movie 6.4 ______ is one correct reason why Okazaki fragments are created during lagging strand DNA synthesis.
A. B. C. D. ECB3 6-15 DNA is only polymerized in the 3’ to 5’ direction DNA is only polymerized in the 5’ to 3’ th 5’ 3’ direction DNA polymerase requires a 5’-OH on the growing chain incoming nucelosides have a phosphate group attached to their 3’-OH 16 DNA Replication II & PCR 3 BIO 106 Fall 2009 Professor Owen 10/14/2009 Important Enzymes for DNA Replication
• • • • • helicase unwinds the helix (req’s ATP) (req’s RNA primase synthesizes the RNA primers DNA polymerase adds nucleotides to 3’ end DNA ligase joins the DNA fragments together (topoisomerase makes reversible breaks) Telomeres Think about the end of the chromosome, especially especially the lagging strand: Can it be replicated normally? Can you sketch its replication? ECB3 6-18 16 DNA Replication II & PCR 4 ...
View Full Document