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DNA (deoxyribonucleic acid) exists in every living thing. Every cell in your body contains DNA and it is uniquely yours. Most of it is located in the nucleus of our cells.
DNA includes information and instructions for your growth, your development, your reproduction, and how your body functions. The information in your DNA is why you are you. Your complete set of DNA is called your genome.
DNA determines your risk of many diseases and your body’s features, such as eye color and height. Your parents pass this information on to you.
Approximately half of the information in your DNA came from your biological father and a half from your biological mother. However, all of your mitochondrial DNA comes from your biological mother. Only egg cells retain their mitochondria during fertilization.
A single strand of human DNA is approximately 5 feet long, but if you unraveled all of the DNA in your body, it would reach the sun and back again approximately multiple times. The DNA in a single cell’s nucleus is approximately 3 km, which is enough to stretch from the Lincoln Memorial to the US Capitol building.
How is this much DNA in the body?
Packed into each cell are the incredibly long strands. It twists and folds, creating a compact package of information. There are as many as 75 trillion cells in the body, each one of them packed with DNA.
What is DNA Made Of?
DNA contains chemical building blocks known as nucleotides. 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)
Under a high-powered electron microscope, DNA looks like a fine, spiral coil of threads. Some people describe it as a twisted ladder. DNA’s nucleotides are linked into chains, with the phosphate and sugar groups alternating.
A single set of chromosomes contain about 3 billion pairs of DNA.
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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. Certain components of this ladder “stick” to themselves and the pattern is always the same. A always sticks to T and G always sticks to C.
Most DNA lives inside the nucleus of a cell (some is found in the cell’s mitochondria where it generates the energy cells need to function properly). The DNA loops around proteins called histones, forming chromatin.
Each of our chromosomes, we have 46 total, 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 which is a hormone that controls the body’s level of sugar in the blood.
But as important as genes are, they only make up about 3 percent of DNA. Scientists have yet to determine what the remaining 97 percent do. Some believe it’s involved in transcription and translation, but they aren’t sure exactly how this works.
As replication occurs, DNA unwinds, which allows it to copy itself. DNA also unwinds to allow access to its instructions for making proteins and other biological processes, but this doesn’t include cell division. During division, DNA remains in its packed position, which enables it to transfer into the new cell.
When a cell is ready to divide, the DNA helix splits down the middle and separates into two single strands. These 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 “sticky” pattern in all DNA, an A base is added where there is an unpaired T and a C is added where there is an unpaired G. Once all the bases have their assigned pair, a new complete DNA strand exists.
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 informs the cell’s protein-making process. The information within the mNA 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.
There are 20 different types of amino acids, all of which can be placed in different orders to create different proteins.
What Happens If DNA is Damaged?
The simplest answer: cancer can develop.
But damage doesn’t automatically mean you’ll get cancer. DNA is damaged tens of thousands of times each day in each cell. This can cause cancer, but in many cases, cells correct the problems and cancer doesn’t develop. But if a cell is unable to fix the problem, that’s when things go haywire.
It’s overwhelming to consider how many times per day your body is at risk of developing cancer, but it’s even more surprising how often cancer does not occur. The body has a miraculous way of dealing with issues and repairing them in most cases.
What causes the errors?
Errors occur for a variety of different reasons. In some cases, damage occurs within nucleotides. Sometimes nucleotides pair up incorrectly, which leads to mutations. Sometimes there are nicks in strands of DNA which interfere with replication.
Mismatched bases are one of the most common errors. This happens when the “sticky” matches pair up incorrectly. For example, if A is not matched with T, it causes problems. Mismatches occur about once every hundred thousand additions.
The repair process relies on specialized enzymes. There are different types of enzymes and they respond to different types of damage. In the case of mismatched base pairs, the enzyme responsible for correction catches most mismatches right away and cuts off a new nucleotide, and replaces it with the correct match.
Following that, the second set of proteins 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.
Replication is not the only point at which damage occurs. Different molecules can trigger chemical changes in nucleotides. These are caused by external factors, like exposure to tobacco smoke. Most people understand that smoking or exposure to second-hand smoke increases a person’s risk of cancer. This is how it occurs. Compounds in tobacco smoke change the chemical structure of nucleotides.
External forces are not the only cause of chemical changes. Some occur naturally. In many cases, these chemicals have a corresponding enzyme that reverses the damage, but if this doesn’t occur, it leads to problems.
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 was a problem.
There are also things you can do to support the correction process. The less risk you expose your body to, the better it will be at correcting errors and managing the cell division and replication process.
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“How Long Is Your DNA?” BBC Science Focus Magazine, www.sciencefocus.com/the-human-body/how-long-is-your-dna/.
“DNA Explained: Structure and Function.” www.medicalnewstoday.com, www.medicalnewstoday.com/articles/319818.
Elert, Glenn. “Glenn Elert.” Hypertextbook.com, 2009, hypertextbook.com/facts/1998/StevenChen.shtml.
National Human Genome Research Institute. “Deoxyribonucleic Acid (DNA) Fact Sheet | NHGRI.” Genome.gov, 2015, www.genome.gov/about-genomics/fact-sheets/Deoxyribonucleic-Acid-Fact-Sheet.
“What Happens When Your DNA Is Damaged? - Monica Menesini.” TED-Ed, ed.ted.com/lessons/what-happens-when-your-dna-is-damaged-monica-menesini.