Genetics Digest aims to provide you with helpful information about DNA analysis and Genome Technology advancements. We are affiliated with CRI Genetics.

Understanding DNA: The Layman's Guide

By Helen Santoro

In 2003, the Human Genome Project successfully mapped the entire sequence of genes in human DNA. Since then, DNA and genetic testing have been all over the news, and the science behind it can leave your head spinning if you’re not familiar with what DNA is or how it works.

A basic knowledge of DNA and genetics can help you understand the implications of all the emerging information about the human genome and decide whether new genetic testing options are worth the investment in light of your personal health concerns.

What is DNA?

DNA stands for deoxyribonucleic acid and is the familiar “double helix” molecule forming the building blocks of every living organism. In your body, DNA is tightly coiled up into chromosomes, and each chromosome contains a specific number of genes. The total number differs depending on the chromosome, of which there are 23 pairs or a total of 46. At conception, you get one set of chromosomes from your mother and another from your father, giving you a unique combination of characteristics expressed as what’s known as your genetic code.

Each DNA double helix is made up of two strands of nucleotides and a collection of nitrogenic bases. Nucleotides have three parts:

  • A sugar molecule called deoxyribose
  • A phosphate group
  • A nucleic acid

The four bases, adenine (A), thymine (T), cytosine (C) and guanine (G), link together in various combinations of base pairs and determine the characteristics of the nucleotide. Within your DNA, you have three billion pairs of nitrogenic bases, creating enough genetic material to stretch for billions of miles if it was laid out in a straight line.

If you could get a look at a DNA molecule, you’d see the sugar and phosphate “strands” on the outside of the helix and the bases running between the strands like the rungs of a ladder. These “rungs” are the basic components of what makes you different from every other human being.

Where is DNA Found?

DNA is housed inside all the cells of your body. Most of it resides in the nucleus of each cell and is called nuclear DNA. The rest is inside the mitochondria, the small organelles within cells responsible for energy production, and is known as mitochondrial DNA.

There are about two meters of DNA inside each cell, or just over 6.5 feet. The tight “packaging” of DNA into chromosomes makes it possible for this much genetic information to be contained in such a small space. Every time a cell divides, an identical copy of this lengthy double strand is made to ensure new cells have the same sequence of base pairs as the originals.

What is the Function of DNA?

Although over 99 percent of the bases in your DNA are identical to those in other people, the remaining fraction of a percentage is unique to you and influences everything from how cells differentiate in the womb to your risk for genetic diseases. Think of the letters representing the bases as an alphabet used to create the “words” making up your genetic sequence. With the exception of identical twins, no two people have exactly the same sequence of base pairs in their DNA. These differences have an influence on the outcomes of the two biggest functions DNA performs.

Making Proteins

Proteins play a multitude of roles in your body, and it’s up to DNA to provide the code from which individual proteins are made. When a specific protein is required:

  • The DNA code is copied to create a single-stranded molecule called messenger RNA (mRNA)
  • Another type of RNA, known as transfer RNA (tRNA), “reads” the code from the mRNA in groups of three bases at a time
  • These groups, or codons, tell the body which amino acids are needed to make the protein

Every codon represents a single amino acid, and the thousands and thousands of possible combinations are what accounts for the complexity of the human body. The process is turning out to be even more complex than was first thought as scientists look into external mechanisms, including diet and lifestyle choices, with the potential to affect how genes are expressed via proteins.


When cells divide, the DNA double helix “unzips” down the middle to form two separate strands. Complimentary copies are made and attached to the unpaired bases, creating an identical strand of DNA for the new cell. If there’s an error in the process, the body usually destroys the mutation to prevent the error from replicating in the future. However, when this doesn’t happen, the resulting mutation can become the basis for disease. DNA errors like these may or may not cause problems depending on whether or not mutated genes are expressed when proteins are made.

DNA Testing: Professional or Home?

Several companies now offer direct-to-consumer (DTC) genetic testing, promising information about your heritage or disease risk at a fraction of the cost of professional testing. However, these tests are often inaccurate and can result in unnecessary anxiety or panic if disease markers are detected. Having a gene known to make you more susceptible to a disease doesn’t mean the disease will actually develop, and the complexity of how an environment can affect gene expression makes these tests even more questionable in terms of precision.

Professional testing is usually accompanied by genetic counseling before and after the test is administered. This gives you a more accurate idea of what your results mean and the changes you can make to improve your health or reduce your risk of developing a particular condition. These tests can also reveal if you’re a carrier of a particular genetic mutation you could pass on to your children and help you make decisions regarding your choice to start a family.

Whether or not you get a genetic test, remember DNA is just one part of a much bigger and more complex picture. Everything you do has the potential to influence how genes are expressed and proteins are created or change the way the “building blocks” of your genetic code influence the development or suppression of disease.

It’s amazing to think the diet and lifestyle decisions you make every day affect your body at a microscopic level, but those very same decisions can determine your disease risk and the number of vibrant years you enjoy. With or without a test to show what health changes may be on the horizon as you age, understanding the importance of proper DNA function should influence how you take care of your body today and throughout your life.

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