What Is DNA? Structure, Function, Pictures & Facts

DNA stands for deoxyribonucleic acid. It's made up of units of biological building blocks called nucleotides.

DNA is a vitally important molecule for not only humans, but for most other organisms as well. DNA contains our hereditary material and our genes — it's what makes us unique.

But what does DNA actually do? Keep reading to discover more about the structure of DNA, what it does, and why it's so important.

Your expansive genome

The complete set of your DNA is called your genome. It contains 3 billion bases, 20,000 genes, and 23 pairs of chromosomes!

You inherit half of your DNA from your father and half from your mother. This DNA comes from the sperm and egg, respectively.

Genes actually make up very little of your genome — only 1 percent. The other 99 percent helps to regulate things like when, how, and in what quantity proteins are produced.

Scientists are still learning more and more about this 'non-coding' DNA.

DNA damage and mutations

The DNA code is prone to damage. In fact, it's estimated that tens of thousands of DNA damage events occur every day in each of our cells. Damage can occur due to things like errors in DNA replication, free radicals, and exposure to UV radiation.

But never fear! Your cells have specialized proteins that are able to detect and repair many cases of DNA damage. In fact, there are at least five major DNA repair pathways.

Mutations are changes in the DNA sequence. They can sometimes be bad. This is because a change in the DNA code can have a downstream impact on the way a protein is made.

If the protein doesn't work properly, disease can result. Some examples of diseases that occur due to mutations in a single gene include cystic fibrosis and sickle cell anemia.

Mutations can also lead to the development of cancer. For example, if genes coding for proteins involved in cellular growth are mutated, cells may grow and divide out of control. Some cancer-causing mutations can be inherited while others can be acquired through exposure to carcinogens like UV radiation, chemicals, or cigarette smoke.

But not all mutations are bad. We're acquiring them all of the time. Some are harmless while others contribute to our diversity as a species.

Changes that occur in more than 1 percent of the population are called polymorphisms. Examples of some polymorphisms are hair and eye color.

DNA and aging

It's believed that unrepaired DNA damage can accumulate as we age, helping to drive the aging process. What factors can influence this?

Something that may play a large role in the DNA damage associated with aging is damage due to free radicals. However, this one mechanism of damage may not be sufficient to explain the aging process. Several factors may also be involved.

One theory as to why DNA damage accumulates as we age is based in evolution. It's thought that DNA damage is repaired more faithfully when we're of reproductive age and having children. After we've passed our peak reproductive years, the repair process naturally declines.

Another part of DNA that may be involved in aging are telomeres. Telomeres are stretches of repetitive DNA sequences that are found at the ends of your chromosomes. They help to protect DNA from damage, but they also shorten with each round of DNA replication.

Telomere shortening has been associated with the aging process. It's also been found that some lifestyle factors such as obesity, exposure to cigarette smoke, and psychological stress can contribute to telomere shortening.

Perhaps making healthy lifestyle choices like maintaining a healthy weight, managing stress, and not smoking can slow telomere shortening? This question continues to be of great interest to researchers.

The DNA molecule is made up of nucleotides. Each nucleotide contains three different components — a sugar, a phosphate group, and a nitrogen base.

The sugar in DNA is called 2'-deoxyribose. These sugar molecules alternate with the phosphate groups, making up the 'backbone' of the DNA strand.

Each sugar in a nucleotide has a nitrogen base attached to it. There are four different types of nitrogen bases found in DNA. They include:

• adenine (A)
• cytosine (C)
• guanine (G)
• thymine (T)

The two strands of DNA form a 3-D structure called a double helix. When illustrated, it looks a little like a ladder that's been twisted into a spiral in which the base pairs are the rungs and the sugar phosphate backbones are the legs.

Additionally, it's worth noting that the DNA in the nucleus of eukaryotic cells is linear, meaning that the ends of each strand are free. In a prokaryotic cell, the DNA forms a circular structure.

DNA helps your body grow

DNA contains the instructions that are necessary for an organism — you, a bird, or a plant for example — to grow, develop, and reproduce. These instructions are stored within the sequence of nucleotide base pairs.

Your cells read this code three bases at a time in order to generate proteins that are essential for growth and survival. The DNA sequence that houses the information to make a protein is called a gene.

Each group of three bases corresponds to specific amino acids, which are the building blocks of proteins. For example, the base pairs T-G-G specify the amino acid tryptophan while the base pairs G-G-C specify the amino acid glycine.

Some combinations, like T-A-A, T-A-G, and T-G-A, also indicate the end of a protein sequence. This tells the cell not to add any more amino acids to the protein.

Proteins are made up of different combinations of amino acids. When placed together in the correct order, each protein has a unique structure and function within your body.

How do you get from the DNA code to a protein?

So far, we've learned that DNA contains a code that gives the cell information on how to make proteins. But what happens in between? Simply put, this occurs via a two-step process:

First, the two DNA strands split apart. Then, special proteins within the nucleus read the base pairs on a DNA strand to create an intermediate messenger molecule.

This process is called transcription and the molecule created is called messenger RNA (mRNA). mRNA is another type of nucleic acid and it does exactly what its name implies. It travels outside of the nucleus, serving as a message to the cellular machinery that builds proteins.

In the second step, specialized components of the cell read the mRNA's message three base pairs at a time and work to assemble a protein, amino acid by amino acid. This process is called translation.

The answer to this question can depend on the type of organism that you're talking about. There are two types of cell — eukaryotic and prokaryotic.

For people, there's DNA in each of our cells.

Eukaryotic cells

Humans and many other organisms have eukaryotic cells. This means that their cells have a membrane-bound nucleus and several other membrane-bound structures called organelles.

In a eukaryotic cell, DNA is within the nucleus. A small amount of DNA is also found in organelles called mitochondria, which are the powerhouses of the cell.

Because there's a limited amount of space within the nucleus, the DNA must be tightly packaged. There are several different stages of packaging, however the final products are the structures that we call chromosomes.

Prokaryotic cells

Organisms like bacteria are prokaryotic cells. These cells don't have a nucleus or organelles. In prokaryotic cells, DNA is found tightly coiled in the middle of the cell.

What happens when your cells divide?

The cells of your body divide as a normal part of growth and development. When this happens, each new cell must have a complete copy of DNA.

In order to achieve this, your DNA must undergo a process called replication. When this occurs, the two DNA strands split apart. Then, specialized cellular proteins use each strand as a template to make a new DNA strand.

When replication is completed, there are two double-stranded DNA molecules. One set will go into each new cell when division is complete.

DNA is pivotal to our growth, reproduction, and health. It contains the instructions necessary for your cells to produce proteins that affect many different processes and functions in your body.

Because DNA is so important, damage or mutations can sometimes contribute to the development of disease. However, it's also important to remember that mutations can be beneficial and contribute to our diversity as well.