Carcinogens

What is definition of carcinogens?
What are mechanisms of actions?
What are the sources of carcinogens?
How can we identify and classify carcinogens?

What is definition of carcinogens?
It is any cancer-causing substance, chemical or physical, such as benzene, cadmium, asbestos or certain types of radiation. The term cancer refers to a type of neoplasm, defined as a new growth (plasia). Cancer is a type of neoplasm characterized by tissue undergoing rapid and abnormal growth. Tissues that grow faster tan the surrounding tissue form an enlarged mass of cells referred to as tumor.

Teratogens

What is the mechanism of teratogenic action?
What are teratogenic agents? 

The most dangerous effect of exposure to a toxic substance occurs when it impacts fetal development and the birth of a child. At birth, the number of children identified as having either a major or minor malformation is approximately 5 percent. Toxic agents that cause abnormal development resulting in birth defects are referred to teratogens.

Mutagens

How many kinds of mutations?
Is it possible for DNA restoration? 

How many kinds of mutations?
There are several types, they are spontaneous mutations, induced mutations, large and point mutations, somatic and germinal mutations.

Spontaneuos mutations
Mutations that occur without the introduction of an exogenous (outside) mutagenic agent. Various types of chemical reaction in the cell may cause these types of mutations. This type of mutation can be caused by the broken of sugar-four bases by chemical intermediates (superoxide, OH radicals, hydrogen peroxide) produced during metabolism, deamination, methylation, some mistakes made by endogenous enzyme in replicating DNA, and some additions or deletions of bases during DNA replication (may occur when there are short complementary base sequences located in the same DNA strand).

How UV can cause skin cancer

UV is a physical agent that can cause mutation of our skin. UV from the sun is known to cause cancer as a result of prologed exposure. UV radiation affects the bonds between adjacent pyrimidines located on the same or opposite DNA strands. When this happens, thymine, for example, will bond to thymine forming a T-T dimer called cyclobutyl thymine. Radiation also causes single strand breaks, double strand breaks and various types of DNA base damage.

Single strand breaks are more easily repaired by the intracellular DNA repair mechanism. While when a double strand break, there are three possible outcomes: 1) the molecule will be connected with no errors, 2) the molecule is repaired incorectly and produces a mutated DNA molecule, or 3) the DNA molecule is not repaired. A DNA molecule with a double strand break results in fragmentation of the chromosomes followed by an abnormal distribution of chromosomes during cell division. This is cancer.

Reference:
Kent, C. 1998. Basics of Toxicology. John Wiley & Sons, Inc. New York