Genetic mutations can alter enzymes which are involved in metabolising nicotine which can later the chances of someone becoming addicted to a substance.
Genetic factors may affect how susceptible a person is to becoming addicted to smoking.
For nicotine dependence 75% of the variation between individuals was explained by genetic factors.
Nicotine will attach to the nicotine resceptors on cells which releases dopamine, this release leads to feelings of joy and pleasure.
The biological approach is not a complete explanation of smoking as it is reductionist.