The Ames test is used to determine if an external agent (such as a chemical) can act as a mutagen. In this test, several different his- strains of Salmonella typhimurium are used. Each strain contains a different class of mutation in the his gene. Each mutant is exposed to the chemical to determine if the chemical can revert the mutation back to wild type (his+), and at what frequency.
(a) How can such prototrophic revertants be identified?
(b) In this experiment, three different strains of Salmonella were used to determine the mutagenic properties of three different chemicals. The following table lists the type of mutation in each his mutant and the number of revertants obtained with the addition of each of the three chemicals. Are any of the chemicals putative mutagens? If so, what type of mutations do they cause? Justify your answer.
Strain Type of his-mutation Water Chemical1 Chemical2 Chemical3
Strain1 T to G base substitution 2 2000 3 5
Strain 2 G to A base substitution 1 1 4 1700
Strain 3 Single base deletion 3 2 4 3.
(a) A petriplate with agar lacking histidine is prepared and the histidine requiring mutant S.typhimurium strain is plated on the petriplate. A filter paper disk soaked in mutagen is placed in the centre of the petriplate. If mutation occurs, the strain regains its ability to synthesisze histidine and will be able to grow on the plate. All the colonies growing on the plate are revertant bacteria ...
The solution assists with identifying prototrophic revertants.
Principles of Toxicology
1) Some theorists argue that there may be no clear threshold for effects such as carcinogenesis & mutation. What arguments do you think they might put forward in support of this?
2) It is important to understand the physiological means by which toxic agents cross cellular membranes & enter the cells of human body. Define & describe both passive & active transport?
3) Definition of toxicology?
4) What do you understand by the term dose? How can you estimate it?
5) What do you understand by the term effect? How is it measured?
6) Using examples distinguish between local and systemic and acute and chronic effects?
7) What do you understand by the term dose - effect and dose - response relations?
8) What is the impact on this relationship if there is more than one effect of a chemical?
9) What do you understand by the term 'threshold of effect'?
10) Define the terms toxico - kinetics and toxico - dynamics?
11) What factors influence chemical:
- Distribution and deposition
- Accumulation and elimination?
12) What do you understand by the term biological half time?
13) What is the significance, when setting threshold for adverse effects, of the fact that, broadly speaking, solid particulates have much longer biological half times than gases and vapours?
14) Briefly, what is the major underlying difference in body handling of a chemical between one and two compartment models of distribution and elimination?
15) Outline some general mechanisms of toxicity?
16) Describe a range of short and long-term toxicity testing methods?
17) Discuss the limitations of animal testing methods in the evaluation of human toxic potential of chemicals?
18) Outline a strategy for testing for carcinogenicity of industrial chemicalsView Full Posting Details