Term
| What two events do elevated P53 levels cause in the cell? |
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Definition
1) Cell cycle arrest
2) A delayed apoptotic signal. If the mutation isn't repaired, this signal occurs. |
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Term
| What 2 events are required in order for a cell to become immortal? |
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Definition
1) Damage tolerance
2) The ability of the cells to restore their telomerases (this is the rate limiting step b/c it happens later) |
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Term
| If there is no response to abnormalities presented in the cell, then P53 is ____________________ or is _________________ . |
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Definition
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Term
| What happens is BCL2 is overproduced? |
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Definition
| It will be tumerogenic because it will prevent the cell from going into apoptosis. It is the product of a protooncogene. |
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Term
| What are telomeric sequences? |
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Definition
| They are complementary strands with one G-rich strand and one C-rich strand. These segments are found at the end of DNA and serve as a protective group. They form a loop at DNA's end and contain telomeric capping proteins. These sequences also have an overhang, the G-rich sequence overhangs the c-rich sequence. |
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Term
| Describe what happens after DNA damage presents itself. |
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Definition
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Term
| Why does DNA shorten after each replication cycle? |
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Definition
| The DNA polymerase needs a space in order to place a primer and use the strand as a template, however, it runs out space and is not able to add more nucleotides. So, one segment isn't replicated. |
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Term
| How to compensate for lack of nucleotides on the telomeric region? |
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Definition
| This is when telomerase comes into play. Telomerase is present in germ line and stem cells. It elongates DNA so that the primer will have enough space. Telomerase functions with RNA polymerase and a RNA sequence that is complementary to the G-rich strand. Then reverse transcriptase elongates the sequence one nucleotide at a time. |
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Term
What three models can be used in humans to see if cells are carcinogenic?
Which model is most useful? |
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Definition
1) Irradiated host - Take healthy mice and give them a high dose of ionizing radiation. This will eliminate their bone marrow and lymphocytic and glucocytic cells.
2) Young, weanlings - Their immune system hasn't fully developed yet and they can't reject the tissue
3) Nude mice - This is the most useful model. A breed of immunocomprimised hairless mice due to a genetic mutation. They have lesions that prevent their thymus gland from maturing and they cannot make T-lymphocytes, which are required for graft rejection. They are very costly to maintain, but they will accept grafts. |
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Term
| What was the purpose of testing cells in the soft agar or suspension culture assay? |
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Definition
To see if cells could survive without anchorage and if they could, do they show contact inhibition.
The question is: Is the loss of the anchorage requirement and contact inhibition related to the carcinogenic potential of the cell? |
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Term
| What procedure would you use to test anchorage dependence of cells? |
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Definition
| You would take cells and inject them into 4-6 week old mice, wait for months, and examine for tumors. Also, you take tissue culture flasks, fill them with tissue culture medium (and with FBS) plus a polymer of suger, glucose or galactose. The presence of the sugar causes the solution to become more viscous and prevents the cells from settling to the bottom of the flask. The flasks are then placed in an incubator at 38 degrees. Then you wait. If the cells have lost anchorage dependence, the cells would divide. After the waiting period, you count how many cells there are in comparison to how many were put in, then you get a percentage. |
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Term
What were the results of Freedman and Shin's anchorage dependence vs malignant transformation test?
Give an example of a malignant and nonmalignant cell used in this experiment. |
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Definition
If the cells divide in solution, they are transformed cells.
Malignant - HeLa
Non-malignant - 3T3 |
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Term
| If HeLa cells are put into a mouse and a tumor begins to form, which cells are proliferating: the HeLa cells or the mouse's cells? |
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Definition
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Term
Describe the characteristics of:
(Chromosome #, anchorage, contact inhibition, life span)
- Primary Cells
- Cell Lines
- Transformed Cells
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Definition
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Term
| If we are given a piece of cervical cancer cells, how do we test if it came from one cell or many? |
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Definition
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Term
| What are three reasons why whole animals aren't the best choice to see if an agent is carcinogenic? |
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Definition
-Time course
-Changes are gradual
-The animal may have a history of malignant cells |
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Term
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Definition
| Tumors on the skin that are caused by exposure to UV light. These tumors are deep and do not normally metastasize. It forms in the keratinocytes and goes into the dermal layer. They grow very slowly. Portions of the skin with hair follicles are more sensitive. It is not invasive; it remains local. It can be detected early because it can be seen on the surface of the skin. |
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Term
| How can UV light form tumors without an initial exposure of cells to an initiating agent? |
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Definition
| 280-320nm (UVB) is the portion of UV light that gets absorbed by the nucleic acids. Photons of UV light exposed to 2 neighboring purimidines, T or C, can cause pyrimidine dimers. |
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Term
| Which 2 products can adjacent thymines form when exposed to UVB light? |
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Definition
1) Cyclobutane thymine dimer (more stable)
2) 6,4-photoproduct |
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Term
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Definition
UVC (200-290nm) is very damaging. That portion of the spectrum never reaches the surface of the earth. It all gets filtered by the ozone.
UVB (290-320nm) is the region of the spectrum where the photons are absorbed by the nucleic acids of the DNA and result in the activation of those bases and consequently the formation of the dimers, so this is mutagenic.
UVA (320-400nm) is more inflammatory. It's not mutagenic but it causes some inflammatory reaction. You can think of it as a promoting agent. It is harmless in a different way than UVB but it still should be filtered because of this promoting factor. |
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Term
| What is Xeroderma Pigmentosum? |
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Definition
1) A defect in the repair mechanism that reverses pyrimidine dimers.
2) Hypersensitivity to light
3) Simple autosomal recessive
4) Seven complementation groups
There are 7 different alleles whose products are involved in the DNA repair of dimers. There named XpA, XpB,...., XpG. For an individual to have Xp, they must have two defective alleles of any one of those |
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Term
| How would you determine how many genes are required to contribute to XP? How would you determine that there are 7 genes related to Xp? |
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Definition
| You can take two mammalian cells and fuse them and those cells will survive for a period. They will have twice as many chromosomes, but they will survive. How do you fuse them? You can incubate the cells in suspension with the virus and polyethyleneglycol and what happens is that the membranes will fuse and then you wash away the viruses and maintain the cells in culture. Then the cells chromosomes will mix. |
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Term
| How How can a mouse knockout study be used to detect the difference between wild type, heterozygous, and homozygous Xp genes? |
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Definition
| A group of knockout mice in which the gene Xpc was knocked out were compared to wild type animals and then to heterozygous. Those animals were exposed to daily doses of UV radiation of their backs. In the Xpc animals, by week 25 all of the animals had basal cell carcinoma. At the same time, the wild type animals did not have any carcinomas. The heterozygous mice were intermediate between the two. That phenomenon is referred to as haploid insufficiency. They could repair the pyrimidine dimers, but not as effectively as the wild type group. |
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Term
How are pyrimidine dimers and PAH-derived adducts removed?
Explain the process. |
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Definition
Nucleotide Excision Repair
First 7 proteins recognize the site, bind to it and become the nucleus for the assembly of other proteins. The proteins nick the DNA about 30 bp's apart, then DNA polymerase comes in, using the unaffected strand as a template to fill the gap, this is followed by DNA lipase, which closes the gap by forming phosphodiester bonds. |
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Term
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Definition
| Melanocytes are cells that are responsible for the pigments of our hair, skin, and eyes. That come from neural crest cells. Within melanocytes are melanosomes in which tyrosine forms polymers. The bags of melanin, the melanosomes, are then carried to the keratinocytes and surround the nucleus in order to protect the cells from the effects of UV light. Skin pigmentation is a result of this process. |
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Term
| What causes varying skin pigments? |
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Definition
| The type of melanin produced and the degree of exchange of that pigment between the melanocytes and keratinocytes. |
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Term
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Definition
Cancer derived from melanocytes. Melanocytes represent 10% of the proliferating cells in the epidermal layer.
It's due to the accumulation of mutations in the melanocytes that result in invasive cancer that is highly immortal and in part it's because melanocytes are predisposed to leave the sites of the tumor and invade other cells. |
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Term
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Definition
During embryonic development, the period in which the ectoderm, the outer layer of the growing embryo folds in itself causing the formation of the neural tube. That outer layer sort of folds and invaginates and results in the formation of a tube that essentially becomes the CNS. And the neural crest cells are cells that came from the ectoderm that sort of get trapped between the neural tube and the ectoderm. Those cells migrate during embryonic development and end up forming a variety of structures.
Because of their function embryonically, are predisposed to migrate. |
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Term
| What are 3 factors that effect malignant melanoma risk? |
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Definition
1) Sunburns before the age of 20
2) # of moles >2 mm diameter
3) Familial links |
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Term
| What happens when we get a brief tan (2-3 hours) compared to a tan that lasts 8-10 months? |
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Definition
A brief tan is due to us being briefly exposed to UVA & UVB. It is due to the redistribution of melanosomes and the pigments within the melanocytes.
The longer tans are cause by an exposure to UVB and an increase in pigment, melanin, production due to more melanosomes and a slight increase in the # of melanocytes. Also, there is an increase in the rate of transfer of the melanosomes to the keratinocytes. |
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Term
| What causes an increase in the propensity of melanocytes to metastasize when transformed? |
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Definition
| Transformed melanocytes seem to reexpress some of the genes that existed earlier on during the fetal developmental stages. One particular gene is SLUG, whose products regulate the ability of the cell to move. |
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Term
| What is the main gene affected when melanocytes are transformed? |
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Definition
| CDK1 which regulates progression through the cell cycle |
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Term
| What did William Henry Perkin discover and why was it dangerous? |
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Definition
He discovered aniline dyes. These dyes are not soluble in water, but can be dissolved in alcohol.
Workers in factories that produced these dyes developed cancer of the urinary bladder. Our body has developed ways to convert lipid-soluble compounds to soluble compounds so that they can be excreted in the urine or feces. The issue with aniline dye is that multiple mutagenic side reactions take place in the process of this conversion. |
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Term
1) Are PAHs soluble in water?
2) Where do PAHs accumulate?
3) How are they eliminated? |
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Definition
1) No
2) In membranes and fatty tissues
3) They are metabolized for elimination. They are converted to a water soluble product in order to be excreted and in the process multiple mutagenic side reactions take place. |
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Term
| Describe the steps taken to detoxify PAH |
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Definition
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Term
Where does phase 1 take place?
Where does phase 2 take place? |
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Definition
1) In the enzymes embedded in the smoothER
2) In the cytoplasm |
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Term
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Definition
| Any one of many proteins that consist of a protein component that is associated with a poryphin ring and typically an iron metal that can be +2 or +3. |
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Term
What is the function of Phenobarbital?
What does it increase the production of? |
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Definition
Leads to proliferation of the smoothER
The enzymes that work in Phase 1 and monooxygenase |
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Term
| What is the equation for Phase 1? |
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Definition
| Substrate + O2 ----(NADPH + H+ --> NADP+)----> Epoxide + H2O |
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Term
What form of P450 are we focusing on?
How is it induced in skin? |
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Definition
1) CY1A1
2) By topical application of benz(a)anthracene |
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Term
Describe the pathway that ends with the production of P450. |
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Definition
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Term
At the end of phase 1, what could happen to BP-7,8-diol that would cause it to become mutagenic?
Why is it mutagenic? |
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Definition
The same monooxygenase or a neighboring monooxygenase can interact with BP-7,8-diol and form BP-7,8-diol-9,10-epoxide which is VERY mutagenic.
It is mutagenic because it can spontaneously form covalent bonds, adducts, with guanine and adenine bases. When DNA polymerase comes to replicate the strand, it will misread the base. |
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Term
| What repair mechanism corrects DNA adducts? |
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Definition
| Nucleotide Excision Repair |
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Term
| How do you determine if an agent causes adducts in the DNA? |
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Definition
| You can use a plasmid and insert a small segment of DNA with a known sequence. Then this plasmid is exposed to the agent, then you let whatever happens happen. Then you insert this plasmid into bacteria and you let the bacteria amplify. Then you sequence the plasmid and look for changes in the DNA sequence. If you see G--> T or A-->T substitution, then an adduct is present. |
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Term
| What was the result of the experiment when benzopyrene and the mutagenic form of benzopyrene were injected into New-born Swiss-Webster mice? |
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Definition
| The derivative was 150 times more mutagenic than benzopyrene |
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Term
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Definition
| Bruce Ames developed a model to test agents for carcinogenic abilities through using a bacterial model, Salmonella typhimurium. He used His- bacteria, which prevented them from making Histidine and prevented replication. So, you have Histidine requiring bacteria. Some are serving as control and some are serving as experimental. 1 mL of those cells, basically a billion cells, is plated on an agar dish with the minimal medium so the cells that survive have to make Histidine. The experimental group is given the agent. And the number of revertants is what’s counted the next day. If you get a greater number of revertants in the experimental, it means that it was mutagenic. |
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Term
| What agents are most effective in chemotherapy? |
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Definition
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Term
| What is the most prominent change when bases are exposed to an alkylating agent? |
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Definition
O6 alkylation of guanine causing a G-->T transformation.
This causes DNA polymerase to misread that base. |
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Term
| How does the cell repair DNA bases effected by alkylating agents? |
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Definition
It uses O6-methyl-guanine-DNA methyl-transferase that recognizes the side group and remove it.
This repair system is very expensive to cells because it will bind and then transfer the alkyl group to itself. This is then degraded. The protein is not used again. For every base that is corrected, a small protein is destroyed.
It has a limited efficiency if the cell of tissue is exposed to high levels of these alkylating agents. |
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Term
| What two things make tobacco a very effective carcinogenic agent? |
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Definition
| Tobacco contains NNK, NNAL, and NNN. Two of them can function as alkylating agents and they all can form adducts with DNA bases as a result of monooxygenase activity. |
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Term
| The more ______________ an agent can produce, the more likely it is to be a ________________ agent. |
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Definition
1) Mutation
2) Transforming |
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Term
| What is the difference in susceptibility between slowly and quickly proliferating cells? |
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Definition
| Slowly proliferating cells will be less susceptible to DNA damage because more would be in G1 phase and can be paused by P53 at the G1/S checkpoint. Quickly proliferating cells are more susceptible because more cells will be in S phase and will be passed the checkpoint. |
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Term
| How would you synchronize cells in the cell cycle using the cell in a culture plate? |
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Definition
1) Temperature control. Low to high
2) Remove FBS and add it back again |
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Term
| What repair mechanism (two types) is used to repair oxidative deamination? Explain. |
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Definition
Base Excision Repair
1) The repair system involves first the cleavage of the bond between the base and the sugar by DNA glycosylase, while leaving the backbone in tact.
Then one or more nucleotides are used to repair this patch.
The first reaction is the removal of the base that results in apurinic acid (DNA w/out one or more purines). The next step is the removal of the remnant of that nucleotide and the insertion of the appropriate nucleotide.
2) The next type of base excision repair involves an incision in the nucleus using a unique enzyme that will cleave the backbone of the DNA missing the base. Depending on the organism and the cell type, one or few DNA nucleotides are added to fill this gap by the DNA polymerase and the DNA ligase. |
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Term
| Two examples of agents tested by the Ames test |
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Definition
AF-2, the food preservative for meat
Hair dyes (90% were mutagenic) |
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