In this article I will look at the biological implications of radioactivity. We all know that radioactive materials are dangerous and can be carcinogenic; but how many of us know why this is so?
There are three common types of ionising radiation: alpha, beta and gamma. Alpha radiation is a helium nucleus made up of two protons and two neutrons and is the most ionising of all types of radiation as it can most easily cause the loss of an electron from a molecule. Beta radiation is a high energy electron and is the second most highly ionising radiation. Finally gamma waves are very high frequency electromagnetic radiation. However the order of harmfulness is not as simple as it first appears as the order of penetration is the reverse of the ionisation with gamma rays being the most penetrating. Alpha radiation is easily stopped by a thin sheet of paper; however it takes a thin sheet of metal to stop beta radiation and a very thick sheet of metal is required in order to stop gamma radiation.
Ionisation in biology can cause a whole host of problems for example the loss of an electron from an organic molecule, we’ll call it RH in this case leads to RH+ and e-. This RH+ then breaks down in order to release H+ and an R radical. This R radical has an unpaired electron and so is highly reactive as it no longer has a full outer shell of electrons and so will react in order to reobtain this configuration.
These radicals can then react with biological molecules such as DNA that can cause a change in the DNA helical structure and so when replication occurs base mismatch can occur and so the wrong base can be added into the daughter strand of DNA. The incorporation of the incorrect base in a DNA sequence is known as a mutation and so radiation is a mutagen. If this mutation occurs in a gene that regulates the replication of a cell such that cell division is increased then the cell is said to be cancerous and so in this way radiation can cause mutations.
