This site is 100% ad supported. Please add an exception to adblock for this site.

Molecular Biology Exam II


undefined, object
copy deck
What do DNA replication errors that change a base-pair sequence cause?
What are the different kinds of mutations?
Point mutations, Deletions, and Insertions
What are Point Mutations?
a substitution of one base for another
What are Deletion Mutations?
When bases get removed
What are Insertion Mutation?
When bases get added.
Name the types of Point Mutations.
Transition mutation and Transversion mutation
What is a Transition Mutation?
A switch from one purine:pyrimidine to the other purine:pyrimidine (example: AT to GC)
What is a Transversion Mutation?
A switch from purine:pyrimidine to pyrimidine:purine (example: AT to TA, AT to CG
How are Point Mutations classed?
By Expression
When are Mutations important?
If they change the expression of the gene.
What do Missense Mutations do?
They change in base-pair changes amino acid; they may change phenotype.
What is a Neutral Mutation?
If there is no change in function.
What is a Silent Mutation?
Base-pair changes without changing amino acid (due to redundancy)
What is a Non-sense Mutation?
A change in base-pair creates stop codon & truncated protein that almost always changes phenotype.
What do deletions or insertions of base-pair numbers that are NOT multiples of 3 cause?
Frame shift mutations
What do Frame Shift Mutations cause?
They produce non-functional protein and can change expression even if they are a multiple of three.
What are some causes of Mutations?
Mismatches during replication, Looping during replication, Spontaneous changes, Damage by water, Chemical damage, and Radiation Damage
What do Mismatches during replication can cause?
Point Mutations
What does Looping during replication cause?
Insertions or Deletions
What does Template Loop cause?
Replicated strand loop causes what?
What do mismatches to enol form?
What is Depurination?
When A or G is lost when base-deoxyribose bond
What is Deamination?
When you remove amine from cytosine get uracil (remove amine from methylated cytosine get thymine)
How is Chemical Damage Induced?
Induced by DNA exposure to alkylating or oxidizing chemicals
What base is especially vulnerable to chemical damage?
Name some Base modifiers.
5-BDU, nitrous acid
Name some Intercalating agents.
acridine orange, ethidium bromide
How is Radiation Damage induced?
Induced by UV, gamma radiation, X-rays
What can UV form?
Thymine-Thymine Dimers
What can cause a single or double bond to break?
Gamma or X-rays
How are DNA breaks repaired?
By Recombination
How are Replication mismatches repaired?
By Polymerase Proofreading
What is activated when proofreading fails?
A mismatch repair system.
What does a Mismatch Repair System correct?
It corrects replication mismatches missed by proofreading
What does Long Patch Repair rely on?
The fact that E. coli adds methyl groups to A in GATC before replication
In E. coli mismatch repair, what happens to GATC sites?
GATC sites are hemi-methylated
In which strands do methylation occur?
Parental Strands
In which strands does un-methylation occur?
Daughter Strands
What slides along new strands shortly after replication & binds to mismatch bulge?
MutS protein
To what does MutS bind to simultaneously?
What binds MutS-ATP when it pauses at mismatch?
MutL protein
What binds to un-methylated strand at hemi-methylated sites but stays inactive?
MutH protein
What activates MutH to nick un-methylated strand at nearest GATC?
What activates UvrD, a helicase, to unwind DNA from nick past the mismatch?
What removes bases from 3’ nick to MutL:MutS?
Exonuclease I
What removes bases from 5’ nick to MutL:MutS?
Exonuclease VII
What fills in gaps using methylated strand as template causing DNA ligase seals the break?
What repairs mismatches in humans?
Since no methlyation occurs in humans what can be used?
Nicks at the primer site
What does MSH detect in Humans?
Bulge and interacts with PCNA
How can Chemical or radiation damage can be repaired?
By direct repair or excision repair systems
What happens in Direct Repair?
Photoreactivation repairs pyrimidine dimers and Methyltransferase transfers methyl from O6-methylguanine to an internal cysteine
What happens in Excision Repair?
See slide 19
What happens if damage is not repaired prior to replication?
The replication fork stalls at lesion.
What will Special trans-lesion polymerase do?
Synthesize over damage
In E. coli what is UmuC complexed to?
Give characteristics of Special trans-lesion polymerases.
They are template dependent,
Nucleotide addition is independent of base-pairing, they are Highly error prone
When do Normal replication polymerases return to the replication fork?
Once undamaged DNA is reached
When would a replication fork stall at lesion?
As a Last Resort

Deck Info