MBG (Molecular Biology) SUMMARIZED
STUDY GUID LATEST UPDATED.
Intragenic Suppressors means the suppression will happen on
The same gene on a different site,
EG.
1st mutation is TTA -> TTT
2nd mutation is TTT -> CTT
Now this restores the original amino acid sequence
Intergenic Suppressors mean the suppression happen due to
A mutation on a second site on a different gene hides the mutation on the first
site in a different gene
EG.
Non-functional protein produced due to nonsense mutation,
Mutation of a tRNA can allow the tRNA to pair with a stop codon allowing
translating to continue,
NOT THE SAME protein as the initial protein, but allows the protein to function
the tRNA here also has a gain of function mutation, as it is allowed to bind to
a stop codon
Mispairing due to other structures can happen by,
A wobble which is flexibility in the DNA structure due to shifting backbone or
protonated form of certain bases
Difference between wobble pairing of G and T and tautomeric pairing of G
and T
Wobble pairing of G and T only has 2 H bonds and both are in common form
Tautomeric pairing of G and T has 3 H bonds, and Guanine is in enol form
,Difference between wobble pairing of A and C and tautomeric pairing of A
and C
Wobble pairing of A and C has a protonated Adenine,
Tautomeric pairing of A and C has Cytosine in imino form
BOTH have 2 H bonds
Incorporated error happens when
And a replicated error happens when
Incorporated error happens newly synthesized DNA
Replicated error happens on next round of replication
Strand slippage can cause
Insertions or deletions,
Changes the reading frame, if they're outside of the reading frame less likely
to have an effect; BUT if they're in a promoter region where a transcription
factor needs to bind like TATA box may be detrimental
Unequal crossing over during meiosis can cause
One chromosome to contain an insertion and the other to contain a deletion
Deamination is
Loss of an amino group
Usually Cytosine -> Uracil
OR
Methylated Cytosine -> Thymine
Over time genomes become increasingly ... poor and ... rich
GC poor and AT rich
Base analog 5-Bromouracil is an analog of ...
Causes what mutation after 2 rounds of replication
5BU is analog of Thymine
G:::C -> G::5BU -> A::5BU -> A::T
,G - > A transition
Alkylating agents are mutagens that react with DNA bases and add ...
What are 2 alkylating agents
Methly CH3 or ethyl CH3-CH3 groups
EMS and Mustard Gas
Can deamination be spontaneous?
Yes it can be spontaneous OR induced
Name a deamination chemical
Nitrous acid
C -> T
A -> hypoxanthine (A -> G transition)
G -> xanthine (G -> A transition)
Hydroxylamine adds
A hydroxyl group to cytosine
Increasing occurence of rare tautomer that pairs with adenine
ONLY AFFECTS CYTOSINE
C -> T transition
Oxidative radicals are
Reactive forms of oxygen H2O2 produced through normal aerobic
metabolism
Can also be produced by chemicals and radiation
end result is
G -> T transversion RARE
Some Intercalating agents are
Cause
Ethidium bromide, acridine orange, dioxin, proflavin
Sandwich themselves (intercalate) between adjacent base pairs distorting
DNA helix
Causes insertions and deletions -> FRAMESHIFT mutations
, Ionizing radiation caused by X-rays can
Break phosphodiester bonds leading to double-stranded breaks
UV radiation can
Induce chemical bonds between two adjacent pyrimidine molecules on the
SAME strand of DNA
Mismatch Repair (MMR)
If a mismatched base was added to the new strand in DNA replication,
what would happen in MMR
Methylation at a GATC sequence, old strand is methylated and the mismatch-
repair complex brings the mismatched bases close to the methylated GATC
sequence and the new strand is identified
Exonucleases remove nucleotides on the new strand between the GATC
sequence and mismatch
DNA polymerase then comes to replace the nucleotides correcting the
mismatch, and DNA ligase seals the nick in the sugar-phosphate backbone
Do eukaryotes have methylated DNA
No
Direct repair is,
Changing of the nucleotides, NOT removing, restoring original structure
Direct repair steps
Photoreactivation of UV induced pyrimidine dimers, breaks the covalent bond
in the dimers when photolyase is activated by the absorption of blue light,
then enzyme is released
CHANGES THE NT themselves
Enzyme called O6-methylguanine-DNA methyltransferase removes the methyl
group from O6-methylguanine restoring the base to guanine
Base-excision repair steps
STUDY GUID LATEST UPDATED.
Intragenic Suppressors means the suppression will happen on
The same gene on a different site,
EG.
1st mutation is TTA -> TTT
2nd mutation is TTT -> CTT
Now this restores the original amino acid sequence
Intergenic Suppressors mean the suppression happen due to
A mutation on a second site on a different gene hides the mutation on the first
site in a different gene
EG.
Non-functional protein produced due to nonsense mutation,
Mutation of a tRNA can allow the tRNA to pair with a stop codon allowing
translating to continue,
NOT THE SAME protein as the initial protein, but allows the protein to function
the tRNA here also has a gain of function mutation, as it is allowed to bind to
a stop codon
Mispairing due to other structures can happen by,
A wobble which is flexibility in the DNA structure due to shifting backbone or
protonated form of certain bases
Difference between wobble pairing of G and T and tautomeric pairing of G
and T
Wobble pairing of G and T only has 2 H bonds and both are in common form
Tautomeric pairing of G and T has 3 H bonds, and Guanine is in enol form
,Difference between wobble pairing of A and C and tautomeric pairing of A
and C
Wobble pairing of A and C has a protonated Adenine,
Tautomeric pairing of A and C has Cytosine in imino form
BOTH have 2 H bonds
Incorporated error happens when
And a replicated error happens when
Incorporated error happens newly synthesized DNA
Replicated error happens on next round of replication
Strand slippage can cause
Insertions or deletions,
Changes the reading frame, if they're outside of the reading frame less likely
to have an effect; BUT if they're in a promoter region where a transcription
factor needs to bind like TATA box may be detrimental
Unequal crossing over during meiosis can cause
One chromosome to contain an insertion and the other to contain a deletion
Deamination is
Loss of an amino group
Usually Cytosine -> Uracil
OR
Methylated Cytosine -> Thymine
Over time genomes become increasingly ... poor and ... rich
GC poor and AT rich
Base analog 5-Bromouracil is an analog of ...
Causes what mutation after 2 rounds of replication
5BU is analog of Thymine
G:::C -> G::5BU -> A::5BU -> A::T
,G - > A transition
Alkylating agents are mutagens that react with DNA bases and add ...
What are 2 alkylating agents
Methly CH3 or ethyl CH3-CH3 groups
EMS and Mustard Gas
Can deamination be spontaneous?
Yes it can be spontaneous OR induced
Name a deamination chemical
Nitrous acid
C -> T
A -> hypoxanthine (A -> G transition)
G -> xanthine (G -> A transition)
Hydroxylamine adds
A hydroxyl group to cytosine
Increasing occurence of rare tautomer that pairs with adenine
ONLY AFFECTS CYTOSINE
C -> T transition
Oxidative radicals are
Reactive forms of oxygen H2O2 produced through normal aerobic
metabolism
Can also be produced by chemicals and radiation
end result is
G -> T transversion RARE
Some Intercalating agents are
Cause
Ethidium bromide, acridine orange, dioxin, proflavin
Sandwich themselves (intercalate) between adjacent base pairs distorting
DNA helix
Causes insertions and deletions -> FRAMESHIFT mutations
, Ionizing radiation caused by X-rays can
Break phosphodiester bonds leading to double-stranded breaks
UV radiation can
Induce chemical bonds between two adjacent pyrimidine molecules on the
SAME strand of DNA
Mismatch Repair (MMR)
If a mismatched base was added to the new strand in DNA replication,
what would happen in MMR
Methylation at a GATC sequence, old strand is methylated and the mismatch-
repair complex brings the mismatched bases close to the methylated GATC
sequence and the new strand is identified
Exonucleases remove nucleotides on the new strand between the GATC
sequence and mismatch
DNA polymerase then comes to replace the nucleotides correcting the
mismatch, and DNA ligase seals the nick in the sugar-phosphate backbone
Do eukaryotes have methylated DNA
No
Direct repair is,
Changing of the nucleotides, NOT removing, restoring original structure
Direct repair steps
Photoreactivation of UV induced pyrimidine dimers, breaks the covalent bond
in the dimers when photolyase is activated by the absorption of blue light,
then enzyme is released
CHANGES THE NT themselves
Enzyme called O6-methylguanine-DNA methyltransferase removes the methyl
group from O6-methylguanine restoring the base to guanine
Base-excision repair steps
