How Long is Human DNA?
Updated on March 18, 2024
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How Long is Human DNA?

A single strand of unraveled human DNA is approximately six (6) feet long, but if you unraveled all of the DNA in your body, it would measure about 67 billion miles long, about 150,000 trips to the moon.1

DNA strands are packed into every cell—all 75 trillion of them. They twist and fold, creating a compact package of information. There are miles upon miles of genetic information inside you, all contributing to who you are.

Because the DNA molecule has a unique double helix structure, it coils upon itself very tightly to pack all the information and fit inside your cells. Your DNA structure makes it possible to hold all the instructions necessary.

How Long is Human DNA? 7

Where is DNA Stored?

A human cell will store DNA mostly in the nucleus. However, a special kind of DNA called mitochondrial DNA that comes only from your biological mother is stored in the mitochondria.3

This is because we inherit our mitochondria from our mothers, as only egg cells retain their mitochondria during fertilization.

Mitochondrial DNA contains information that sustains your mitochondria. Their DNA structure is a little different from nuclear DNA. Unlike the double helix structure in nuclear DNA, the mitochondrial DNA molecule is made up of two circular strands of information.

Each of our chromosomes contains one DNA molecule. Our chromosomes contain genes. Each length of DNA codes for a specific gene. For example, there is a gene code for insulin, a hormone that controls the body’s blood sugar level.

What is DNA?

DNA, or deoxyribonucleic acid, is the building block of your identity. It includes everything you need to make sure you function and make you unique.

DNA includes information and instructions for your growth, your development, your reproduction, and how your body functions. The genetic information in your DNA dictates your physical features, determines some personality traits, and determines your risk of many diseases.

The whole set of instructions and genetic material in your DNA is called the human genome.

How Long is Human DNA? 8

What is DNA Made Of?

DNA contains chemical building blocks known as nucleotides.2

These are made of three parts: a phosphate group, a sugar group, and one of four types of nitrogen bases, including:

  • Adenine (A)
  • Cytosine (C)
  • Guanine (G)
  • Thymine (T)

These nitrogen bases pair up and form a chain across two DNA strands. One DNA strand will have a sequence of nitrogen bases that go all the way down its length, alternating among any of the four. The complementary strand will have its own sequence of nitrogen bases.

Certain nitrogen bases only connect with other specific ones. Adenine’s complementary base is Thymine, so every instance of Adenine in a DNA strand will only connect with Thymine in the complementary strand. The same goes for Cytosine and Guanine.

What Does DNA Look Like?

Under a high-powered electron microscope, DNA looks like a fine, spiral coil of threads.

There are two strands that intertwine and coil, joined by chains. Some people describe it as a twisted ladder. DNA’s nucleotides are linked into chains, alternating between the phosphate and sugar groups.

A single set of chromosomes contains about 3 billion pairs of DNA, and these pairs are what give the DNA chain its double helix shape.

How Long is Human DNA? 9

Where Does DNA Come From?

You inherit genetic information from your parents, which builds your DNA.

Approximately half of the information in your DNA comes from your biological father, while the other half comes from your biological mother.

A sperm cell and an egg cell both only carry half a set of chromosomes, which are just one strand of what is usually the double-stranded DNA molecule. A DNA strand from the father will meet up with a complementary strand from the mother, and these two DNA strands join together to create a full set of chromosomes.

Your DNA is the result of this unique union.

What is the Structure of DNA?

Scientists call the structure of DNA a double helix. It’s a two-stranded molecule that twists around itself and looks like a spiral ladder.

How Long is Human DNA? 10

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How Does DNA Replicate?

When human cells are ready to divide, the DNA helix first splits down the middle and separates into two single strands. Before cells are able to divide, the DNA must first replicate itself.

These now-single strands are the template for creating the two new double-strands of DNA. Each new strand is an exact replication of the original strand.

So based on the patterns that follow nitrogen bases in all DNA, an Adenine base is added where there is an unpaired Thymine, and a Cytosine is added where there is an unpaired Guanine. A new complete DNA strand exists once all the bases have their assigned pair.

Every DNA molecule that results from this is identical to its predecessor.4

Additionally, as the body creates proteins, the double helix unwinds and allows a single strand of DNA to be the template.

This template is transcribed into mRNA. mRNA is a messenger (that’s what the m stands for) that triggers the cell’s protein-making process. The information within the mRNA molecule is translated so the amino acids understand it. It tells the cell the order in which to link amino acids to create a specific protein. 

Why Does DNA Replicate?

DNA replicates because when cells divide and multiply, so does the DNA. It’s necessary because the instructions to make these cells the exact same as the rest of your cells are stored in your DNA.

Before any cell divides, the DNA must first replicate itself, ensuring that the resulting cell properly inherits your genome and all the necessary information for that organism.

Human cells constantly do this. You can observe it, especially when you’re still growing, healing a wound, or renewing your tissues.

How Long is Human DNA? 11

What Happens If DNA is Damaged?

DNA is often damaged without much consequence throughout the day, as cells can often self-correct these errors.

However, if cells can’t address the damage, several serious conditions or predispositions to them can develop, such as:5

  • Genomic instability
  • Cancer
  • Senescence
  • Neurological disorders

What Causes the Errors?

Errors occur for a variety of different reasons and can be a result of errors in metabolic processes within cells or environmental factors.

In some cases, damage occurs within nucleotides. Sometimes nucleotides pair up incorrectly, which leads to mutations.

This happens when the pairs match up incorrectly during replication. For example, if Adenine is not matched with Thymine, it causes problems. Mismatches occur about once every hundred thousand additions.

Other instances of damage may involve or occur in:5

  • Radiation
  • Oxidation
  • Hydrolysis
  • Exposure to chemicals or chemical agents
How Long is Human DNA? 12

How Does DNA Repair Itself?

The repair process relies on specialized enzymes. There are different types of enzymes that respond to different types of damage.

In the case of mismatched base pairs, the enzyme responsible for correction catches most mismatches right away, cuts off a new nucleotide, and replaces it with the correct match. 

The second set of proteins then runs a “cross-check,” further reducing the risk of an error. This two-step process reduces the risk of a mismatch to about one in one billion.

Additionally, cells also have general repair options. The human body is intelligent and self-healing. It repairs mistakes and damage before you even know there is a problem.

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Updated on March 18, 2024
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6 sources cited
Updated on March 18, 2024
  1. “UCSB Science Line.”, Accessed 1 Mar. 2021.

  2. “How Long Is Your DNA?” BBC Science Focus Magazine,

  3. “DNA Explained: Structure and Function.”,

  4. Elert, Glenn. “Glenn Elert.”, 2009,

  5. National Human Genome Research Institute. “Deoxyribonucleic Acid (DNA) Fact Sheet | NHGRI.”, 2015,

  6. “What Happens When Your DNA Is Damaged? – Monica Menesini.” TED-Ed,

Dr. Dhingra
Dr. Harshi Dhingra
Medical Reviewer
Dr Harshi Dhingra is a licensed medical doctor with a specialization in Pathology. Dr. Dhingra has of over a decade in diagnostic, clinical, research and teaching work, including managing all sections of Pathology laboratory including histopathology, cytology, hematology and clinical Pathology.
Kelly Brown
Kelly Brown
Content Contributor
Kelly has experience working with clients in a variety of industries, including legal, medical, marketing, and travel. Her goal is to share important information that people can use to make decisions about their health and the health of their loved ones. From choosing the best treatment programs to improving dental and vision health to finding the best method for helping anyone who is struggling with health issues, she hopes to share what she learns through informative content.