Cells, the basic units of every living system, are directed by the DNA (deoxyribonucleic acid) within the cells. The illustration below shows that DNA has a particular side-by-side arrangement that resembles a ladder.


This arrangement determines the unique traits of all living organisms. Each rung of the ladder is called a base pair.   A DNA nucleotide (an organic compound which is a subset of a cell’s DNA) consists of a molecule of sugar, a molecule of phosphate, and a molecule called a base.  Each base pair contains two of the following chemicals–adenine, thymine, guanine, and cytosine. In DNA, the code letters are A, T, G, and C.  Adenine always pairs with thymine, and guanine always pairs with cytosine.

The complete set of DNA of an organism is called a genome. A complete genome is contained in every cell, except for red blood cells. A bacterium is the smallest known genome and it has over 600,000 base pairs, while human genomes have over 3 billion base pairs.  

Each human cell’s DNA is packaged into 46 chromosomes arranged into 23 pairs. Each chromosome is a separate molecule of DNA that can contain from 50 million to 250 million base pairs. 

Some abnormalities in chromosomes can be detected by microscopic examination, but most require an analysis of each base unit. 

Genes are pieces of DNA, and most of the estimated 25,000 genes in a human cell, comprising about 2% of the total genome, contain directions for making specific proteins.  These proteins are large, complex molecules made up of chains of small chemical compounds called amino acids. 

All the proteins in a cell are called its proteome. While the genome changes infrequently, the proteome changes constantly as it responds to tens of thousands of intracellular and extracellular environmental signals.    

It is the person’s DNA that determines their body size and shape, hair color, eye color, etc. DNA determinations on blood are done with the DNA present in white blood cells.  Approximately 99% of each person’s DNA is the same person to person. It is the 1% that accounts for the differences in each of us.

Everyone’s body is constantly creating the beginnings of brain tumors, but most of our bodies destroy them before they can grow.  Others develop brain tumors—some are cancerous and some aren’t. These events are all controlled, in large part, by instructions from our DNA.

Theoretically, there are few “diseases” that our body could not defeat—if all things were working properly. Some people eat fatty foods all their lives, smoke cigarettes, drink alcohol and never exercise, but never have clogged heart arteries and live until age 90. Others never eat fatty foods, don’t drink alcohol, exercise all the time and still develop clogged heart arteries and die at age 50. Again, it depends on our DNA.
Once a drug is in the body, our DNA will dictate how the drug is to be handled by the body. Sometimes the enzymes in the P450 pathway that are created according to instructions from a person’s DNA do not work in the way that they work in most other people. These variations in DNA are called alleles (ALL-EELS’). Sometimes, certain enzymes are not even created at all, and it is known that people with certain alleles are more susceptible to a particular disease than most people.  

It is one’s DNA and any variations in it that will determine how drugs and/or alcohol are metabolized and how they affect each of us.