Term
| Is there any sort of predictability in regards to mutations? |
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Definition
No; mutations are spontaneous, statistically random events unrelated to the "need" of an organism (although mutations are useful for natural selection, not every mutation is actually useful since some can actually be fatal for an organism) |
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Term
| What did the Lederberg's replica plating experiments find? |
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Definition
Their experiment found that adaptive mutations can already be present even before the actual process of selection begins |
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Term
| What are the three major origins of mutations? |
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Definition
Replication errors, spontaneous chemical changes and chemically induced mutations |
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Term
| What are 2 forms of spontaneous chemical changes which could result in DNA mutation? |
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Definition
Depurination (loss of a purine base, A or G) and deamination (loss of an NH2 group from the base or changes of cytosine to uracil or methylated cytosinve to thymine) |
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Term
| What system is used when depurination happens (the loss of a G or A base)? |
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Definition
If the issue isn't repaired a potentially incorrect nucleotide (usually adenine) will be incorporated. If the missing base was adenine to begin with then there is no negative effect. If a new sequence is formed and both G and A within the codon produce the same amino acid in the sequence then there will be no negative effect. If the codon isn't the same then there is a mutation |
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Term
| What happens during deamination in regards to the change in bases? |
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Definition
The amino group on cytosine could be replaced with an oxygen atom (and therefore the cyclic N would receive a hydrogen atom) which would result in the production of uracil. Methylation of the uracil would produce thymine. Also, the same mechanism as in the previous example could apply to 5-methylcytosine which would result in a direct transition to thymine instead of having to go through a second reaction mechanism |
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Term
| What are five examples of chemical mutagens? |
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Definition
Base analogs, alkylating agents, deaminating chemicals, oxidative reactions and intercalating agents |
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Term
| How does the base analog 5-bromouracil affect DNA? |
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Definition
It can pair correctly with adenine but it mispairs with guanine. 5BrU loses the 3-hydrogen and the nitrogen becomes negatively charged |
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Term
| Describe how 5BrU affects DNA mutation |
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Definition
Upon initial replication an original adenine pairs with 5BrU. Another strand separation produces one strand with the good initial A while the faulty 5BrU is left behind. When the faulty 5BrU is used in the template it mispairs with guanine and changes the base. Provided that this mismatch keeps occuring more and more mutant DNA molecules will be produced if detection is faulty or simply doesn't occur |
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Term
| What base mutation can guanine undergo and what effect does this have? |
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Definition
| The double-bonded oxygen can shift a bond to an ethyl ion which results in O-ethylguanine. This base mispairs with thymine and produced GC to TA mutations |
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Term
| What effect do oxidative radicals have on guanine and what effect could this product have? |
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Definition
The hydrogen on the sp2 carbon between the nitrogens in the 5 member ring can be replaced with an oxygen atom. The result of this could mispair with adenine |
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Term
| What effect do intercalating agents have on DNA? |
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Definition
Intercalating agents insert or delete base pairs |
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Term
| What effect does ultraviolet radiation have on DNA and what effect does this have? |
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Definition
UV light forms covalent bonds between pyrimidine bases (C and T) but primarily between 2 Ts. This blocks replciation, transcription and cell division |
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Term
| What radiation source accounts for more than 5x the radiation produced by the next leading source? |
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Definition
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Term
| What were some effects from the Chernobyl blast on local people and what were some statistics from the case? |
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Definition
10x more radiation than the Hiroshima nuke was released which, all said, came out to the same exposure levels of about 1,000 chest x-rays per person. High thyroid cancer rates in children ensued and about 4,000 deaths were seen out of the 6.6 million people most highly exposed to the radiation |
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Term
| How does the Ames test work in determining mutagenic chemicals? |
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Definition
His- bacteria are prepared in 2 vials and a substance of interest is added to one. After incubation the control plate should have little to no growth but the experimental group may have growth; if the experimental plate has more growth then the substance added is likely mutagenic |
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Term
| What are the three common DNA repair mechanisms? |
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Definition
Mismatch repair, base-excision and nucleotide-excision |
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Term
| What are some errors that mismatch repair fixes within the DNA? |
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Definition
It can fix replication errors including mispaired bases and strand slippage |
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Term
| What are some genetic mutations that base-excision (AP endonuclease) can fix? |
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Definition
It can fix abnormal bases, modified bases and pyrimidine dimers (NOTE: this does not include mutations which distort the double helix; these mutations are fixed by nucleotide excision) |
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Term
| What are some types of mutations that nucleotide-excision can repair? |
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Definition
Nucleotide-excision can repair abnormal bases, modified bases and pyrimidine dimers which distort the double helix |
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Term
| How does the process of mismatch repair work? |
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Definition
| If a mismatched base was added to a new strand then MutL and MutS recognize and bind to the mismatch. MutL then stimulates MutH to nick the strand between the GATC site and the mismatched base and exonucleases remove the nucleotides on the new strand between GATC and mismatch. DNA polymerase then replaces the nucleotides and DNA ligase seals the nick |
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Term
| How the base-excision repair (AP endonuclease) mechanism work? |
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Definition
DNA glycosylase recognizes and removes the damaged base leaving a base-free site (AP site). AP endonuclease cleaves the phosphodiester bond on the 5' sides of the AP site and removes BOTH the deoxyribose sugar and the phosphate group. DNA polymerase then comes in and addes what should be the correct matching base into the void and DNA ligase seals the gap |
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Term
| How does the nucleotide-excision repair mechanism work? |
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Definition
It removes bulky DNA lesions such as pyrimidine dimers. Repair endonuclease enzyme complex recognizes damage and binds to DNA which is then made into ssDNA and ss-binding proteins stabilize the ssDNA. An unspecified enzyme cleaves the strand on both sides of the damage and DNA polyermase/ligase fill the resulting gap |
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