Anti-carcinogens are: (PGI Dec 2007)
**Core Concept**
Anti-carcinogens are substances that prevent the formation or growth of cancer cells, thereby inhibiting the development of cancer. They can act through various mechanisms, including the inhibition of carcinogen metabolism, DNA repair, or cell cycle arrest.
**Why the Correct Answer is Right**
The correct answer is a type of anti-carcinogen that acts by inhibiting the activity of carcinogens, thereby preventing their transformation into mutagenic or carcinogenic compounds. This is achieved through the inhibition of enzymes involved in the metabolism of carcinogens, such as cytochrome P450. By preventing the formation of carcinogenic intermediates, anti-carcinogens can reduce the risk of cancer development.
**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because it is a type of carcinogen, not an anti-carcinogen. Carcinogens are substances that can cause cancer, whereas anti-carcinogens prevent cancer formation.
**Option B:** This option is incorrect because it is a type of medication that is used to treat cancer, not prevent it. Chemotherapy agents can be used to kill cancer cells, but they do not prevent the formation of cancer cells.
**Option C:** This option is incorrect because it is a type of substance that can cause cancer, not prevent it. Tobacco smoke contains carcinogens that can increase the risk of cancer.
**Clinical Pearl / High-Yield Fact**
It is essential to note that anti-carcinogens can be found in various forms, including dietary compounds, such as polyphenols and isothiocyanates, which have been shown to have anti-cancer properties.
**Correct Answer: D. Ascorbic acid**