BIO 351 Lecture Notes - Lecture 9: Dna Polymerase Iii Holoenzyme, Dna Polymerase Ii, Dna Polymerase
Mutation and Chromosomal Variation Objectives
1. What are some benefits and dangers of mutations?
− Benefits: genetic variance among a population allows for environmental flexibility and evolution
− Dangers: could lead to recessive LOF and many diseases (including cancer)
− Successful organisms have thus evolved the means the repair their DNA efficiently but not too efficiently,
leaving just enough genetic variability for evolution to continue
2. Identify the four ways DNA sequences can change. Associate these turns with all the examples of mutation
below (substitution, deletion, insertion, inversion)
− Substitution = a single nucleotide is substituted with (or exchanged for) a different nucleotide
− Deletion = an omission of one or a few nucleotides
− Insertion = an addition of one or a few nucleotides
− Inversion = a few nucleotides switch direction or invert
− Identifying the ones from class
o A mismatch can turn into a substitution (if undergoes 2 rounds of DNA replication)
o Slippage can turn into an insertion (backwards) or deletion (forwards) on a small scale
o Slippage can also turn into duplication on a larger scale Ex. (untington’s disease
o Deamination can turn into a substitution
o Thymine Dimer (from UV exposure) can turn into a one base pair deletion
3. Distinguish between a mismatch, an incorporated mismatch, and a mutation
− Requires TWO rounds of DNA Replication for a mismatch to become a mutation
4. How are mismatches repaired? How are incorporated mismatches repaired in prokaryotes? (proofreading,
exonuclease activity, DNA methylation, DNA methylase, DNA Polymerase, endonuclease)
− Cell has two opportunities to fix the mistake
− DNA Polymerase ))) has proofreading abilities and can perform 3’ to 5’ exonuclease activity to backspace
a mismatch
− If it becomes an incorporated mismatch, now Mismatch Repair Enzymes can try to remove it
o Endonuclease = removes incorrect nucleotide and sound around it, creating a gap
o DNA Polymerase II, IV, and V (prokaryotes) then go in and add base pairs to fill the gap
o DNA Ligase fixes the last nick in the sugar-phosphate backbone
find more resources at oneclass.com
find more resources at oneclass.com
− But how does the Endonuclease know which nucleotide to fix?
o There are periodic palindromic sequences throughout the DNA that DNA Methylase will mark with
– CH3 (this process is called DNA Methylation)
o Older DNA will be more methylated, while newer DNA will be less methylated (simply bc of
exposure of time in cell)
o Endonucleases target the less methylated strand
5. Diagram how DNA slippage can result in the insertion or deletion of a single nucleotide (DNA replication)
− Slippage = a during replication, either strand loops
out a bit, resulting in the addition/omission of a
nucleotide base (or more)
− Breathing = local unzipping of double strand
− This is where DNA Polymerase gets confused and
doesn’t know exactly where it left off
6. (ow do trinucleotide repeats expand during DNA replication? (ow is this related to (untington’s disease?
− Trinucleotide repeats are a problem area for DNA Polymerase
o Makes a lot of mistakes bc prone to slippage
o Backward Slipping can become an insertion (and extend the trinucleotide repeat)
o Forward Slipping can become a deletion
− (untington’s Disease is associated with an expanded trinucleotide repeat CAG
o Occurs in one of the biggest proteins
o Expressed in the brain (and testes for males) (neurodegenerative disorder)
o Triplet repeat codes for the same amino acid over and over and over again
o Extra glutamic acids warp protein conformation and prevent proper function
− Increased trinucleotide region is associated with increased penetrance and earlier onset
o <26 repeats → will not be affected with no risk to offspring
o 27-35 repeats → will not be affected with elevated but very small risk to offspring
o 36-39 repeats → reduced penetrance with 50% risk to offspring
o 40+ repeats → full penetrance with 50% risk to offspring
7. A CG-dinucleotide CpG is when a C and G nucleotide are next to each other in the same DNA strand. CpGs
are rare in eukaryotic genomes… why is this? (methylation, deamination, thymine)
find more resources at oneclass.com
find more resources at oneclass.com
Document Summary
Benefits: genetic variance among a population allows for environmental flexibility and evolution. Dangers: could lead to recessive lof and many diseases (including cancer) Successful organisms have thus evolved the means the repair their dna efficiently but not too efficiently, leaving just enough genetic variability for evolution to continue: identify the four ways dna sequences can change. Associate these turns with all the examples of mutation below (substitution, deletion, insertion, inversion) Substitution = a single nucleotide is substituted with (or exchanged for) a different nucleotide. Deletion = an omission of one or a few nucleotides. Insertion = an addition of one or a few nucleotides. Inversion = a few nucleotides switch direction or invert. How are incorporated mismatches repaired in prokaryotes? (proofreading, exonuclease activity, dna methylation, dna methylase, dna polymerase, endonuclease) Cell has two opportunities to fix the mistake. Dna polymerase ))) has proofreading abilities and can perform 3" to 5" exonuclease activity to (cid:498)backspace(cid:499) a mismatch.
