Copying DNA Flashcards
E. Coil. VS Humans
- Very Similar in rate of Mutation
- Humans: Replicate DNA even when we haven’t reproduces
- E. Coli: Replicates=Reproduces every 20-30mins
Mutation Rates
We measure mutations in descendants of One Bacterium
- 1 nucleotide changes for every Billion nucleotides a generation
- mutated nucleotides Die and are Not Inherited
- Histones - Very Conservative (don’t change)
- Fibrinopeptides - Least Conservative protein (changes but no1 cares) sequence doesn’t matter
Why Low Mutation rates are Needed
- High mutation rates would limit the #or possible proteins making them less reliable
- Species wouldn’t be able to mate or reproduce because they would die too fast
- Humans would experience cancer more often
Replication Forks
More like a replication Bubble where new bonds are Always added to 3’
>Leading strand: replication occurs in the same direction as rep. Fork
>Lagging strand: must wait until rep. Fork opens enough to work Backwards.
-creating small fragments called Okazaki Fragments
-not covalent bonded yet
Replication Mistakes
-If the Helix is under any tork or pressure the geometry will be off
Ex: G-T can form 2 hydrogen bonds
>Tautomers: these rare forms of DNA bases mispair w.o a change in helix geometry (1 in 10^4 or 10^5 chance)
Exonucleolytic Proofreading
First: DNA Polymerase
- must change conformation after base-pairing
- Dosent work well is base-paring is off
Next: Exonucleolytic Proofreading (cut ends of nucleotide)
- clips wrong nucleotide off from 3’-5’
- Exonuclease can be separate protein or subunit
Strand-directed Mismatch Repair System
2 Mismatch Proofreading Proteins
-MutS
>detects the mistake
-MutL
>removes the area between the Nick and the Mismatch
-DNA Polymerase
>repair DNA Synthesis by filling the blank
