Saanvi Vavilala, Savaas Iqbal, Neelam Sharma and Hemant Joshi- Tara Innovations LLC, www.tara-marketing.com, [email protected]
Discovering the Code to Life
Code is a system of words, letters, or signs used to represent a message in a secret, shorter or in a convenient form. DNA (deoxyribonucleic acid) is such a code to all living cells in the universe. DNA holds the instruction manual for each living thing for anything from a blade of grass to bacteria, animals, and humans. But what exactly is DNA, and how did we discover it?
Even centuries ago, scientists knew that there was some microscopic molecule inside organisms that encoded its characteristics - causing similar traits to be passed down to off spring. However, scientists were unsure about what this molecule could be. In the 1950s, scientists named the “gene” to be this very microscopic molecule. This elusive “gene” was capable of replicating with little to no error, a biological machine that is key to all life as we know it.
The chemistry, structure, and replication of genes were unknown to scientists. Only after all the main groups of macromolecules—proteins, sugars, and lipids—were ruled out, was an amazing discovery about to occur. Watson & Crick are credited to have discovered the double helix structure of DNA (Figure 1).
Through rigorous study of genetics, biochemistry, chemistry, physical chemistry, and X-ray crystallography—the secrets to modern molecular biology were uncovered. Numerous contributions were also made by a British chemist Rosalind Franklin and a New Zealand born biophysicist Maurine Wilkins. Franklin’s discovery allowed for the final pieces of the puzzle to come together, with Photo 51, an x-ray crystallography image captured by her PhD student, RG Gosling (Figure 2).
What is DNA?
DNA stands for Deoxyribonucleic Acid. This large and intimidating word actually tells us a lot about DNA’s structure. The prefix “deoxy” means that there is no oxygen atom attached to one of the carbon atoms, and this fact differentiates DNA from its closely related relative, RNA, or ribonucleic acids. The “ribo” refers to the ribose sugars that make up the sugar-phosphate backbone of a nucleotide, as can be seen below (Figure 3). Finally, the actual nucleic acids are what create the genetic code, and in DNA, they are ‘A’, ‘T’, ‘C’, ‘G’ or Adenine, Thymine, Cytosine, Guanine, respectively. These nucleotide bases are the fundamental units of the genetic code. Bases A, G, C and T are found in DNA while RNA (Ribonucleic acid) includes a fifth base, Uracil (U). Thymine and Uracil have similar chemical structures, except for the methyl group found in Thymine on the fifth carbon (C5) of the heterocyclic six-membered ring.
The double helix structure is supported by a phosphate-sugar backbone, which provides structural support and prevents strands from breaking apart.
One of the key components to DNA are nucleotides. These nucleotides are the building blocks of DNA. The structure consists of 3 parts: phosphate, pentose (5-carbon) sugar, and a nitrogenous base. These bases then create unique sequences that can code for something entirely different if even just one base is changed. There are two categories of nitrogenous bases, pyrimidines, and purines (Figure 4). Pyrimidines are smaller and pair with the larger purines. Each nitrogenous base pairs with specific other nitrogenous bases.
The purine Adenine pairs with the pyrimidine Thymine, and the purine Guanine pairs with pyrimidine Cytosine.
DNA and Genes
As described above, DNA is a long-chain of nucleotides, and genes are small stretches of DNA. An organism’s genome is the entire collection of DNA and can contain thousands of genes. Genes are so important because they provide the instructions for building proteins, which conduct all sorts of functions, from digesting food to carrying oxygen through our bloodstream. Gene encodes an amino acid sequence of a specific protein. Genes are part of DNAs and RNAs.
How Else Can We Use DNA?
DNA is unique to each and every individual. The human genome contains 3,000,000,000 base pairs arranged in a unique sequence — meaning that DNA can be used to identify any individual. DNA decides traits – a characteristics that is caused by genetics. Traits can be various kinds – personality, physical features, value system, likings etc. Mainly, genes determine traits of an organism. Babies get genes from both parents. As a results, they get traits from their both parents. This fact becomes extremely useful when solving crimes. A person can be identified from even the smallest sample of saliva, blood, urine, or hair!
Additionally, DNA testing can help scientists learn about human history through analyzing migration patterns, disease outbreaks, and pathogens. In the medical field, DNA is used to recognize predisposition to diseases, vaccine development, and cancer therapy. DNA can also be used for cloning, which is the process of making identical genetic offspring by reusing existing DNA.
All of these endeavors became possible due to the Human Genome Project, which lasted 13 years, from 1990 to 2003. It was an ambitious project that was aimed at discovering the sequence of the entirety of human DNA—all 3 billion base pairs! Now that we have access to such a valuable information, it is possible to do all of the processes mentioned above, from DNA finger-printing and catching criminals to creating genetic clones.
Future of DNA Fingerprinting and Gene-Editing
After DNA sequencing became quick, easy, and accessible, scientists began to look for ways to change this code in a precise way. In 2012, American biochemist - Jennifer Doudna, French scientist - Emmanuelle Charpentier, discovered CRISPR-Cas9 (Clustered, Regularly-Interspaced Short Palindromic Repeats), a technology that allows scientists to cut and edit genomic sequences with high accuracy. CRISPR itself was first found in bacteria, which used this mechanism to splice and edit their own genetic sequences to remove viral infections. By combining CRISPR with the protein Cas9, Doudna and Charpentier were able to create a technology with endless possibilities, most notably the ability to genetically modify crops, livestock, and even human beings. Major ethical considerations come into play with editing human DNA. These modifications can be passed down from generation to generation, possibly subjecting the entire human population to the creation of “designer babies,” or the concern that people would begin to choose their children’s eye color, height, athletic ability, and more.
With gene-editing technology, creating genetically-modified organisms (GMOs) becomes even easier. GMOs are typically found in produce, common medicines, and animal products. Since the 1970s, organisms have been modified for various purposes. The labeling of GMO products, the safety of consumption, and the ethical considerations of consuming GMOs have been notoriously controversial. Many nations restrict the consumption of certain genetically-modified organisms, and many people believe that altering what is natural is something that shouldn’t’t be done. On the other hand, proponents of GMOs argue that creating better, stronger crops and medicines that can help the world’s people is more important than these concerns.
DNA has influential applications in the field of medicine too. For example, DNA is used to design vaccines. Since viruses can’t reproduce on their own, they enter human cells and use human genetic materials in the cells to replicate themselves. Viruses replicate so quickly and as a result, they evolve extremely quickly, making them more virulent or weaker. Therefore, new vaccines are constantly being made to keep up with the changing genetic sequences of the invading virus. DNA vaccines use engineered DNA to induce an immunologic response in the host against bacteria, parasites, viruses, and potentially cancer.
Many drugs are not effective in patients or patients experience severe side effects due to some medicines and these might be related to their DNA. We are moving towards more personalized medicines. We are moving away from the conventional “one drug and one dose fits all” approach. We will be focusing on our DNA in the future to develop personalized medicines.
In the future, we can expect to see newer and more complex gene editing tools, capable of engineering solutions to century-old problems. For example, scientists have already begun to develop cures to seizure disorders caused by mutations in the HCN1 gene and other long-term treatments for genetic disorders such as gene therapy. While nobody truly knows what the future may hold, we can say with certainty that DNA’s importance and the presence of gene editing is here to stay.
Author Biographies
Saanvi Vavilala graduated from the Academy for Biotechnology at Mountain Lakes High School, and will be majoring in cell and molecular biology at the University of Texas at Austin while pursuing a career in biological laboratory research.
Savaas Iqbal graduated from the Academy for Biotechnology at Mountain Lakes High School, and will be pursuing STEM at Cornell University’s College of Engineering.
Editor’s Note: Hemant Joshi and his colleagues at Tara Innovations are frequent contributors to American Pharmaceutical Review and Pharmaceutical Outsourcing magazines. Tara offers summer internships to students interested in science. During their internship students learn how science is applied to real-world situations.
American Pharmaceutical Review is proud to publish this article written by two of Tara's 2022 interns.
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