DNA, RNA, chromosomes, genes, codons, amino acids, proteins: for many of us, these terms are jumbled together in our minds with other semi-forgotten terms from high school courses. Most of us are familiar with the double helix shape of DNA, but we might wonder: of what does it consist? Where exactly is it located in the body? How can a string of molecules direct the body to grow blue or brown eyes, black or blond hair, a slim or muscular build?

Why Should We Care?

For those of us who are not scientists, genetics might seem a remote concern. Why should we care about how DNA functions?

Dr. Francis Collins, director of the Human Genome Project which “read” the entire sequence of human genes, refers to our DNA as the “language of God.”¹ Even a cursory glance at this molecular wonder reveals beauty and symmetry in its form. All of nature reveals the hand and mind of God, but DNA is unique in revealing the directions He wrote into our most intimate spaces to grow and sustain the only creature made in His image.

Additionally, we should care because we need to make decisions about gene management, on both a personal and a political level. Is it worth spending extra money at the grocery store for GMO free food? Do we want to be screened for genetic markers for disease, now that this is possible? Can we accept genetic modification of human embryos, which is already occurring elsewhere in the world, or will we work to prevent it? Although genetic modification of our offspring might sound like science fiction, Nature, the most frequently cited scientific journal in the world, recently published an article entitled “Should You Edit Your Children’s Genes?” Decisions about genetics are rapidly becoming part of our daily lives.

What is DNA?

Every cell in the body contains a library of instruction books for making body parts. Instead of ink printed on paper, these books are made from a molecule known as DNA (deoxyribonucleic acid).

The cell has a central directing area called the nucleus. This is the library where the body's reference books, written with DNA, are stored.²

As shown above, DNA is constructed like a ladder. The rungs of the ladder are where the information is stored. Each rung consists of two molecules held together by the attraction of positive and negative charge between them. There are only four possible components: the molecules Adenine, Thymine, Guanine, and Cytosine, known as nitrogenous bases. (A base connected to its attached segment of the ladder is referred to as a nucleotide.) Bases fit together in an extremely specific way: A and T can only bond with each other. G and C can only bond with each other. Each grouping, A/T and C/G, is known as a base pair.³

In order to be read by the cell, the DNA ladder needs to be separated into two: the rungs must be broken apart. Each half of the ladder is like a series of open, connected pages of a molecular instruction book written in Braille, with the bases A,T,G, and C acting as letters imparting information to the cell. Since base pairing is so specific, the entire ladder can be replicated from the information contained in one half of it: where A exists on one half of the rung, T must necessarily reside on the opposite half, and so on.⁴

Your entire DNA library, known as your genome, contains six billion nucleotides.⁵ DNA is read by the body in molecular words called codons, each consisting of three nucleotide letters, taken from the A,T, G, and C alphabet.⁶ These are divided among forty-six molecular books, referred to as chromosomes.⁷ Each chromosome contains hundreds to thousands of segments known as genes,⁸ like pages of Braille strung together into one long chain. In order to fit into the tiny nucleus, chromosomes are coiled and stored.⁹ like library books on a shelf, until they are needed for reference. Each cell has an identical copy of the DNA library, or genome, in its nucleus.¹⁰ but each cell only reads the pages it needs, and ignores the others.

Within this library, the chromosomal books are organized into two volume sets. Within each set are two copies of each type of gene, one inherited from your mother and one from your father. This enables the body to follow instructions to construct you so that you are physically like your mother in some ways, and like your father in other respects.¹¹

What Do the DNA Reference Books Tell the Body to Do?

DNA is used as a blueprint for biological macromolecules such as RNA (ribonucleic acid) and proteins.¹² Because the body's parts are largely constructed from various types of protein, storing information about proteins is an essential function.

Proteins are made up of small building block molecules called amino acids. Each of your DNA’s molecular words, or codons, consists of three nucleotide letters and corresponds to a specific amino acid.¹³ The machinery inside your cells uses these codons to construct proteins¹⁴ that make up every part of your body. Proteins vary in size from dozens to thousands of amino acids and are combined or folded into a variety of shapes (or “tertiary structures”) after being built from their component amino acids.¹⁵

While there are only four DNA nucleotide “letters,” they can be used to code for any one of twenty different amino acids.¹⁶ These twenty amino acids are the building blocks used to form any of the billions of unique proteins found in life on earth. You can see how the complexity of DNA quickly scales up from four letters to billions of possible combinations!

Who Visits the Library?

Cells build proteins using small “factories” called ribosomes. Ribosomes need instructions from the DNA reference books to put amino acids together in the proper order to form a protein. These instructions are transferred from DNA (inside the nucleus) to ribosomes with the help of messenger RNA, or mRNA.

Within the nucleus, a protein called RNA polymerase binds to DNA at a “promoter sequence,” like a reader locating a bookmarked page, and begins using nucleotide letters to build a single strand of RNA complementary to the DNA being transcribe.¹⁷ When RNA polymerase reaches the end of the sequence it is transcribing, it detaches from the DNA, freeing the mRNA strand. This strand then leaves the nucleus, where it is bound by ribosomes and used to synthesize a protein.^{18 19} RNA polymerase is like a research assistant inside the DNA library: it can’t take the DNA blueprints outside, but it can make photocopies in the form of mRNA, which are then used as instructions to build proteins.

Can We Change Our DNA Reference Libraries?

One way scientists have tried to change DNA is to bombard cells with new molecular words and sentences. A device called a gene gun injects DNA segments into cells, hoping these get recopied and incorporated into the reference library.²⁰But gene guns can only be used on some types of cells, and they aren’t guaranteed to insert the target sequence at the desired location. Many other genetic engineering techniques exist, but like the gene gun, they have limitations that make them useful only within specific contexts.²¹

What if we could, instead, choose a specific word on a specific page which we wanted to change? A new technology known as CRISPR (Clustered Regularly Interspaced Short Palindromic Repeats) allows scientists to do this. CRISPR is like a pair of molecular scissors: its user can find the specific place in the chain of DNA which needs to change, send the molecular scissors there, cut it out, and replace it.²²

Should We Edit the DNA Library?

We have not yet refined our level of knowledge and precision so that one can enter the womb of a mother, snip out the genes for blue eyes, and replace them with genes for brown eyes. Yet scientists in China have already edited the genes of embryos (in the lab, without implanting them in a woman's womb),²³ and scientists in the U.K. have received government approval to do so. ²⁴ Ought we, as a national and global community, permit this?

When considering the morality of editing genes, we must ask which kinds of DNA we are considering editing: plant, animal, or human? If human, are we discussing editing embryonic, or non embryonic (somatic) cells? Is our purpose to restore an organism to its natural healthy functioning, or to enhance it beyond ordinary natural boundaries? Is there a moral difference between enhancing an ear of corn to be disease resistant, and enhancing a human embryo to be more intelligent, attractive, athletic, etc. than it would have been without intervention?

How to edit genes is a question for science. Whether to edit genes-- and if so, under which circumstances-- is a question of ethics. As public debate moves forward, we must advocate a sound and comprehensive philosophy of life in order to ensure that gene editing technology will be used wisely. The embryos whose genes have already been edited were unable to advocate for themselves. Furthermore, our political rights are based on our fundamental equality; human genetic manipulation used for the purpose of enhancement could disrupt this equality. As Holocaust survivor Elie Weisel has written, “We must always take sides. Neutrality helps the oppressor, never the victim. Silence encourages the tormentor, never the tormented.”²⁵