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41 Cards in this Set
- Front
- Back
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What are the seven types of mutation? |
1) Somatic vs germline 2) silent vs coding 3) frameshifts 4) insertions/deletions 5) forward 6) backward 7) suppressor |
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What are the five causes of mutations (mutagens)? |
1) Base analogues (5 bromouracil)
2) modifying chemicals 3) radiation (UV/infrared) 4) DNA replication 5) DNA recombination (rec A) |
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What are the five types of DNA repair? |
1) light repair 2) excision repair 3) mismatch repair 4) post replication repair 5) error-prone repair system |
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What are silent mutations? |
Mutations that occur in the genome which does not code |
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What are missense mutations? |
changes one amino acid to another one |
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What are nonsense mutations? |
-changes a codon for an amine acid into a stop codon -premature termination -often leads to a loss-of-function |
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Why do viruses have a higher mutation rate? |
They are unable to repair mutations |
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What are the four steps of the light dependent repair system? Factors: T-dimers DNA photolyase |
Step 1) DNA is exposed to UV light causing T-dimers Step 2) DNA photolyase binds to T-dimers Step 3) Photolyase is activated by blue light, cleaves off T-dimers and phophase backbone Step 4) Photolyase is released |
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What are the four steps of the excision repair system? Factors: DNA repair endonuclease DNA polymerase DNA ligase |
Step 1) A DNA repair endonuclease recognises mutation Step 2) Endonuclease binds and excises the damaged base/s. Step 3) DNA polymerase fills the gap using undamaged complementary strand as template Step 4) DNA ligase seals the break left by the DNA polymerase |
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What are the two types of excision repair? |
1) Base excision repair - removes mutated bases 2) Nucleotide excision repair - removes larger defects (T-dimers) |
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What are the four steps in postreplication mismatch repair? Factors: MutS MutH MutL MutU |
1) MutS recognises mismatches and binds to them to initiate repair process 2) MutH and MutL join the complex 3) MutH cleaves unmethylated strand on either side of the mismatch 4) DNApol III fills the gap and ligase seals the damage |
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How does the postreplication repair distinguish between the parent strand, and the mutated new strand? |
The new strand is able to be recognised because the A bases are methylated in the new strands. |
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What are the three steps in the post replication repair? Factors: Rec A DNA polymerase DNA ligase Homologous DNA |
Post replication repair is a ¨last ditch effort¨ Step 1) a thymine dimer blocks replication and synthesis restarts after the dimer, leaving a gap in the complementary strand. Step 2) Rec A binds to strand with the gap and mediates the excision/transplant of homologous DNA to the gap Step 3) After cell division, the dimer and the gap in the homologous DNA will be repaired because they now both have an undamaged complementary strand. |
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What does DNA polymerase do? |
-DNA polymerase can cleave off mutated base pairs -synthesis new DNA -can proofread and correct if there are errors |
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What is the advantage in DNA recombination? |
DNA recombination allows homologous DNA molecules to swap bases and allow for greater diversity |
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What four functions do enzymes need to carry out during DNA recombination? |
During DNA recombination, enzymes need to: 1) Cleave 2) Unwind 3) Repair 4) and join the strands |
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What are mutations? |
-Mutations are the source of all genetic variation -They refer to a change in genetic material -The process by which change occurs |
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Broadly speaking, what are the two categories of mutation? |
1) Changes in chromosome number/structure 2) Mutations at specific points of a gene |
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What does the term mutant refer too? |
A mutant is an organism which exhibits a novel phenotype |
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Do most mutations affect the phenotype, and if so, why? |
Most mutations do not affect the phenotype because they are more likely to fall into the silent region of DNA |
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What are the differences between germline and somatic mutations? |
-Germline mutations can affect the sex cells and can be passed down (transmitted through gametes) -Somatic mutations only effect the individual and cannot be passed on |
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What are the three factors of mutations? |
1) Somatic or germinal 2) Spontaneous or induced 3) Usually random and not adaptive |
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What two factors can increase the rate of mutation? |
-The more cells that can divide, the more likely a mutation will occur -At times when cells are under stress, there is also an increase in rate of mutation |
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What is a forward mutation? |
A forward mutation is the mutation of a wildtype to a mutant. |
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What are reverse and suppressor mutations and what is the difference? |
-Reverse mutations restores the wild type gene by undoing the forward mutation -Suppressor mutations are a second mutation at a different location with which suppresses the first. |
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What is a base substitution mutation? |
-Base substitution only affects one base -There are two types of base substitutions, transitions and transversions |
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What is a transition mutation? |
A transition mutation is the base substitution of one purine to another purine, or a pyrimadine to another pyrimadine. Purine: AG Pyrimadine: TC These are common as it does not change the internal structure of the bases. |
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What is a transversion mutation? |
A transversion mutation is a base substitution of a pyrimadine to a purine or vice versa. Purine: AG Pyrimadine: TC These are less common as it changes the internal structure of the bases. |
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What is an isoallele and a null allele? |
-An isoallele is an allele that mutates and does not affect the phenotype -A null allele is the absence of a gene altogether |
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What are recessive lethal genes? |
-Recessive lethal genes that are lethal for the individual when they are in their homologous states -X-linked recessive mutations are an exception (in males) |
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What are insertions and deletions? |
-An insertion/deletion is when one or more base pairs are inserted or deleted -More likely to happen in a chain of the same bases |
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Where in the DNA sequence can insertions or deletions be dangerous? |
-Insertions/deletions can be dangerous if they occur near the start of DNA sequences -Especially in the binding or promoter sites and can stop the whole sequence being coded |
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Why do X-linked lethal mutations alter the sex ratio? |
-Females have two X chromosomes, so an X-linked lethal mutation can be suppressed by the other X allele -Males cannot suppress X alleles, so they may die from even a recessive X lethal mutation |
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What are conditional lethal mutations? |
-Conditional lethal mutations are lethal in a specific environment -They may also be viable in another specific environment -These mutants may be bred under certain conditions |
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What are the three classes of conditional lethal mutations? |
1) Auxotrophs - Can only grow in certain conditions 2) Temperature-sensitive mutants - organisms that can grow at one temperature or not another 3) Suppressor sensitive mutations - a mutant that is viable only when a suppressor is present |
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What are frameshift mutations? |
-Usually causes from insertions or deletions -DNA bases are reads in groups of 3 -Insertion/deletions alter the reading frame -Insertions/deletions in multiples of three are not so bad since only one amino acid is removed |
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What are taumoter shifts and how do they affect replication? |
-A taumoter shift is the shifting of protons inside the bases -This can happen to any of the four bases -This may cause bases to pair incorrectly -They may affect replication because an C-A bonding will result in different filial strands |
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What is the rare imino form? |
-As a result from tautomer shifts, C may bind to A -C-A bindings are called rare imino forms |
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What is the rare enol forms |
-As a result from tautomer shifts, T may bind to G -T-G bindings are called rare enol forms |
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What is 5-Bromouracil? |
-5-Bromouracil is a thymine analogue -Br increases the frequency of tautomeric shifts -Br can bind with A or G -This can cause problems as G:C pairings may alter to an A:T pairing in just three replications |
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What affect does UV light have on bases? |
-UV light can cause neighbouring bases to form covalent bonds with one another -UV light creates T-dimers |
