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A Deep Dive into DNA and Mutations

We’ve heard so much about DNA in sci-fi movies. Mutations in someone’s DNA can destroy the planet. Whoa, scary! But wait... if we all have DNA inside us, does that mean we’re all capable of destroying others? OMG.

Let’s find out!


DNA 101: A Quick Recap

Our body is made up of trillions of cells. Cells are the building blocks of life, like Lego pieces coming together to form a structure. Each cell contains many different parts that help it function. One of these parts, the nucleus, holds all the genetic material (genome) in the form of DNA.


DNA is a long, thread-like structure that’s tightly coiled, about 2 meters long in each cell! Small segments of DNA are our functional units of heredity: genes. These genes produce proteins (this is called gene expression), which are responsible for various functions in the body. The human genome has around 20,000 to 25,000 genes.


Even though every cell has the same DNA, each type of cell only uses the genes it needs. For example, liver cells and brain cells turn on different sets of genes because they have different jobs and need different proteins. Also, certain genes can be switched on or off as the body grows or in response to things like infections or stress.


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What’s DNA Made Of? Let’s Break It Down

DNA is short for Deoxyribonucleic Acid. It’s a 2-meter-long, thread-like structure with a double helix shape. It’s a biochemical molecule made of specific components that help it maintain its shape and stability, allowing it to carry the genetic information in the body and to pass it on to the next generation.


DNA is made of chemical building blocks called nucleotides. Each nucleotide has three parts: a phosphate group (made of phosphorus and oxygen), a sugar group (called deoxyribose), and one of four nitrogen bases (biochemical compounds that contain nitrogen). To form a strand of DNA, nucleotides link into chains, with the phosphate and sugar groups alternating (as shown in the image below).


The four nitrogen bases in DNA are: adenine (A), thymine (T), guanine (G), and cytosine (C). These four bases make up the “letters” of the genetic code. DNA has its own language, and these four letters form the instructions for the cell. Defined sections of these base sequences make up a gene. The order, or sequence, of the bases determines what biological instructions are contained in a strand of DNA. These instructions are responsible for producing the proteins needed for the body to function each day.


The complete DNA instruction book, or genome, for a human contains about 3 billion bases and around 20,000 to 25,000 genes across 23 pairs of chromosomes (for a total of 46).


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Mutation Station: When DNA Gets a Makeover

Any change in the DNA language, like skipping, adding, or swapping one of the letters, is called a mutation (shown in the image below). Mutations are also called genetic variants, where “variant” simply means a change in the DNA sequence. Not all mutations or variants are harmful. In fact, they are essential to evolution and are the raw material for genetic diversity. This is also why each of us looks different from our parents, siblings, and everyone else.


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Mutations can occur mainly due to a couple of factors:

  • During DNA copying (also called replication)

  • Environmental factors such as UV light, cigarette smoke, harmful radiation, etc. (these are known as mutagens, anything that can cause mutations)


Not All Mutations Are Inherited

Mutations can occur in any cell of the body, but not all of them get passed on to the next generation. Those that occur in non-reproductive cells are called somatic mutations; they affect only the person who has them and may be involved in diseases like cancer (non-hereditary cancers). On the other hand, mutations that occur in reproductive cells (egg or sperm) are called germline or hereditary mutations, and these can be passed down to children. 


So... Do All Mutations Cause Problems?

As our cells divide and grow, the DNA inside each cell has to make a copy (this is called replication) and divide so that each new cell gets the same instruction manual to do its job. During this process, mutations or variants can happen. It’s actually quite common and expected because no biological machinery is perfect. That said, the replication process is highly accurate, with a very low error rate. Most of the time, cells can recognize any potentially harmful changes and repair them before they become permanent mutations.


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But sometimes, these errors, like spelling mistakes in a sentence, can affect the function of a gene. If a gene no longer works or produces a faulty protein, it can increase the chances of certain health conditions. Some examples include cancer, heart conditions, and sickle cell anemia. A mutation will only impact a person’s health if it changes the structure or function of the gene, preventing it from doing its job properly.


Not All Mutations are Bad

Most disease-causing gene mutations are uncommon in the general population. However, other genetic changes occur more frequently. Genetic alterations that occur in more than 1 percent of the population are called polymorphisms. They are common enough to be considered a normal variation in the DNA. Polymorphisms are responsible for many of the normal differences between people, such as eye color, hair color, and blood type. While many polymorphisms have no negative effects on a person’s health, some of these variations may influence the risk of developing certain disorders, depending on where in the genome they occur and how they affect gene function, as discussed earlier. Therefore, all polymorphisms can be considered as mutations, but not all mutations are polymorphisms.



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