Nucleic Acids: The Molecular Architects of Life
In 1869, Friedrich Miescher [Figure 1] discovered and isolated a novel molecule, which is now widely known as DNA, working as a scientist in a laboratory at the University of Tübingen, Germany. It was isolated from a cell’s nuclei and therefore in his first description, Friederich called it nuclein (Dahm, 2008). Almost a decade later, Albrecht Kossel purified and discovered five individual nitrogen bases along with their properties between 1885 and 1901, including adenine, cytosine, guanine, thymine, and uracil (Jones, 1953). The term "nucleic acid" was introduced by Richard Altmann in 1889, at a time when DNA and RNA were not differentiated. The first X-Ray diffraction pattern of DNA was published by William Astbury and Florence Bell in 1938. In 1944, Oswald Avery, Colin MacLeod, and Maclyn McCarty demonstrated that DNA, rather than proteins, carried genetic information. Then, in 1953, James Watson and Francis Crick proposed the double-helix structure of DNA, which revolutionized our understanding of genetics and heredity. This discovery paved the way for significant advancements in the field of molecular biology (Lamm et al., 2020).
The study of nucleic acids is a major part of modern biological and medical research, as well as a foundation for genome research, forensic science, pharmaceutical studies and biotechnology. There are two main types of nucleic acids: DNA and RNA. They are found in nature and carry biological information and genetic material. These acids are very common and are found in every living cell and every form of life on Earth uses these acids to create, encode, and store information. In turn, they send and express that information inside and outside the core of the cell. The discovery of nucleic acids and DNA has lead researchers to comprehensively study all of the DNA (known as a genome) of a select organism, which eventually lead to the Human Genome Project (HGP) (Collins & Fink, 1995).
The Human Genome Project
The international Human Genome Project commenced in 1990 with the ambitious goal of sequencing the complete human genome [Figure 2], which consists of about 3.3 billion base pairs distributed across 23 pairs of chromosomes (Hood & Rowen, 2013).The effort was driven by two international research groups. The initial findings of the first group, a private company known as Celera Genomics, were published in the journal Science in February 2001. Similarly, the preliminary results of the second group, a publicly funded research team called the International Human Genome Consortium, were also published in the journal Nature in February 2001. The project took almost 13 years to complete and researchers were staggered to discover only about 30,000 genes in the human genome. This figure has since reduced to 25,000. This is similar to many other eukaryotes, including some as simple as the roundworm Caenorhabditis elegans (Hodgkin, 2001). The main goal of the human genome project was to; identify all the genes in the human DNA, determine the sequence of the three million base pairs that make up the human DNA, to store the information in a database; improve tools for data analysis, transfer the technology to other industry sectors to be used, and finally address any ethical, legal and social implications (ELSI) that may arise from the project.
The information obtained from the HGP project have and will allow scientists to identify all human genes and determine which set of genes are likely involved in different human traits, including diseases that have a genetic basis. However, the intricate interplay of genes does not necessarily say that a defect in one gene will develop into a particular disease. Nonetheless, some forms of genetic testing have certainly become a routine part of medical testing today. It certainly has proven to be highly advantageous. For instance, individuals with a heightened susceptibility to heart disease can now access this information early on. By making slight adjustments to their diet and lifestyle, they can substantially diminish the risk of developing heart disease. This exemplifies the practical benefits of the project's findings for personalized health management (Collins & Fink, 1995).
The Human Genome Project (HGP, Figure 3) brought forth a myriad of concerns, with one of the foremost being the fear of genetic discrimination stemming from the unrestricted distribution of genetic data. In a rare instance within the realm of scientific projects, the HGP dedicated substantial financial support and research endeavors to the examination of ethical, legal, and social implications. This endeavor raised a range of pivotal questions, such as the extent to which genetic information should be disclosed. Queries surfaced regarding the rights of entities like employers, physicians, prospective spouses, and insurance companies in accessing an individual's genetic makeup. These inquiries constituted a significant aspect of the research underpinning the HGP. The film Gattaca was released in the year 1997, portraying a society that classified and predetermined social and economic class based on an individual’s genetic code. This film's release had triggered widespread concern and mistrust around genetic screening and the possibility of it leading to widespread prejudice and discrimination. Due to a lack of meaningful therapies for conditions associated with potentially harmful genes, the rationale for genetic screening became a point of discussion (Mussgnug et al., 2020).
Additional concerns arose, with some individuals seeking to exploit available genetic information for personal gain and political advantage. Furthermore, there was the looming fear of insurance companies declining coverage to individuals with identified genetic risks. Another disconcerting notion was the prospect of people attempting to eliminate specific genes in pursuit of what society would define as the perfect race. Despite these apprehensions, many couples remained keen on determining whether their offspring might inherit life-threatening diseases through genetic screening (Ashcroft, 2007; Hood & Rowen, 2013).
Identifying gene abnormalities have been made possible by chromosome mapping. It involves identifying the location, structure, and function of each gene on every chromosome in the nucleus. This has been extremely useful in diagnosing diseases, and providing counselling to parents planning to have children. The information gathered and obtained from chromosome mapping has also created possibilities for new gene therapies. Other than giving insight into how the human body functions and works, the research has also helped scientists understand non-human organisms, and DNA sequencing of these organisms has led to a better understanding of their natural capabilities, which have been applied to solve challenging problems in healthcare, agriculture, energy production, and environmental pollution. The research has also opened up a new era of molecular medicine, by looking at the fundamental cause of a disease rather than only treating the symptoms of that particular disease (Hood & Rowen, 2013).
Two specific examples highlight the importance of genetic testing. Women coming from families that present no high risk factors for obtaining breast cancer have no advantage in testing for the disease. An absence of the “high-risk gene” does not provide any information on whether a mutation of the “normal gene” might occur in the future. The risk of breast cancer is not changed if a person has the normal gene, hence why mammograms and monthly self-examinations are in order. Another reason is that the presence of a gene has not always predicted the development of the disease. While Huntington's disease is an incurable neurodegenerative disorder that is inherited, there are some individuals who have shown to be carriers of the disease but have survived to old age without developing the disease's symptoms [Figure 4]. Similarly, some males who have cystic fibrosis related infertility, due to the improper chloride-channel function or lack of sperm canal, only learn this when they go to the clinic to assess the nature of their fertility problem, even though they may never have shown true symptoms of the disease as a child, other than perhaps a high occurrence of respiratory ailments (Franceschi et al., 2018).
Creating "designer babies" or the perfect human using gene therapy is another major concern associated with the HGP, which many people fear is the same as "playing God". However, some have argued that gene therapy is useful in correcting diseases that hinder life or are otherwise deadly. Several diseases are already being tested with human subjects including; severe combined immunodeficiency (SCID, also known as the bubble boy disease), cystic fibrosis and many more. As of now, United States guidelines allow gene therapy of somatic cells, but not genetic modifications that could be passed on to future generations (Gonçalves & Paiva, 2017).
Methodologies of the Human Genome Project
The Human Genome Project used two major methodologies. One approach focused on identifying all the genes expressed as RNA, known as Expressed Sequence Tags (ESTs). The other approach involved sequence annotation, where the entire genome was sequenced, including coding and non-coding sequences, and then assigned different functions to specific regions. In this process, DNA from a cell was isolated and converted into smaller fragments, which were then cloned in suitable hosts using specialized vectors like Bacterial Artificial Chromosomes (BAC) and Yeast Artificial Chromosomes (YAC). The fragments were sequenced using automated DNA sequencers, which were then arranged based on overlapping regions using specialized computer programs, annotated, and assigned to each chromosome. Additionally, genetic and physical maps on the genome were assigned using information on polymorphism of restriction endonuclease recognition sites and repetitive DNA sequences called microsatellites (Mundy, 2001). Novel sequencing techniques like shotgun sequencing are employed to sequence longer DNA fragments, replacing traditional sequencing methods.
Identical Twins and Epigenetics
Identical twins separated at birth have given a lot of insight into the different effects of nature versus nurture [Figure 5]. Studying their differences and similarities has given us much insight into how much of our physiology and our behavior is governed by our genetics. However, even twins raised together in similar environments can exhibit significant differences. Although identical twins share identical DNA, they can exhibit divergent traits due to variations in their epigenetic modifications. Epigenetics is the study of heritable changes in gene expression that are not associated with alterations in DNA sequence, unlike mutations.
Types of epigenetics changes include; DNA methylation, histone modification and non-coding RNA [Figure 6] (Handel et al., 2010; Zoghbi & Beaudet, 2016). A chemical group is added to DNA during DNA methylation. These groups are usually added to specific parts of the DNA, where they block the proteins that attach to DNA to read genes. Genes are normally turned "off" by methylation and turned "on" by demethylation. Histone modification, involves altering histones by acetylation, methylation, phosphorylation, which ultimately affect gene expression. DNA wrap around these histone proteins and modification by these chemical groups influence how tightly the DNA is wrapped around the histones, which in turn affects whether a gene is turned on or off. For example, when histones are loosely packed, more DNA is exposed and accessible to the proteins that "read" the gene, resulting in gene activation. RNA regulation remains less understood compared to other epigenetic mechanisms. It is believed that RNA signaling contributes to epigenetics by influencing chromatin structure. Chromatin refers to the mixture of DNA and proteins that form the chromosomes found in human cells.
Conclusion
Throughout all living organisms, nucleic acids are essential molecules that maintain, transmit, and express genetic information. As different types of nucleic acids, DNA and RNA serve distinct, yet interconnected functions in the cell, with DNA serving as a repository of genetic information and RNA facilitating the translation of genetic information into proteins. There are a number of unique characteristics of nucleic acids, such as the double helical arrangement of DNA, and the single stranded arrangement of RNA. We have gained a great deal of knowledge about genetic information, heredity, and the molecular basis of life through the study of nucleic acids. It has led to ground-breaking discoveries such as the elucidation of the genetic code and the development of techniques such as polymerase chain reaction (PCR) and genetic editing. The capacity to unravel entire genomes has revolutionized agriculture, medicine, forensics, and evolutionary studies.
In addition, synthetic biology and gene therapy harness the potentials of nucleic acids, offering innovative solutions to various medical and environmental challenges. It seems that the possibilities for scientific and technological advancement are endless as we continue to discover the intricacies of nucleic acids and their roles in life. Overall, nucleic acids are the molecular keystones of life, containing the secrets to our genetic inheritance as well as the promise of a brighter and healthier future.
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