notes 11-4

b. Mismatch repair system
i. Find mismatched bases
1. Identified by proofreading enzymes that search for things that aren’t matched – look for kinks in the DNA strands (don’t fit together right if they are mismatched)
2. Have to determine which side is right and which side is wrong – want to make sure that you fix the right strand
a. Keep the older one and delete the newer one (Methylated one)
3. Endonuclease is going to cut the single strand of DNA on the non-methylated strand on both sides of the kink → then, degrades (eats) the stretch of the strand that contains the kink (the bit in between the cuts)
4. Then, DNA polymerase comes into the open area that was created on the strand – connects to the bases already there and then synthesizes the strand and fills in the empty spot with the correct bases
ii. Methylated DNA is older
1. The Methylated strand is the one that we want to keep

How many mutant bacteria are there in a colony of 1 billion E. coli?
• 1.10^9 E. Coli X 5 million bps = 5x10^15 bps in colony
• 5x10^15 bps / 1x10^10 = 500,000

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