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Why Genomics_042323A
[Why Genomics - NIH]

 - Genomics

 Genomics is the study of all of a person's genes (genome), including how they interact with each other and with the person's environment.



Deoxyribonucleic acid (DNA) is a chemical compound that contains the instructions needed to develop and direct the activities of nearly all living organisms. The DNA molecule consists of two twisted paired strands, often called a double helix. 

Each strand of DNA is made up of four chemical units called nucleotide bases, which make up the genetic "alphabet". The bases are adenine (A), thymine (T), guanine (G) and cytosine (C). Specific pairing based on opposite strands: A is always paired with T; C is always paired with G. The order of As, Ts, Cs, and Gs determines the meaning of that part of the DNA molecule that encodes information, just as the order of letters determines the meaning of words.

- Genome

An organism's complete collection of DNA is called its genome. Virtually every cell in the body contains a complete copy of the approximately 3 billion DNA base pairs, or letters, that make up the human genome.

With its four-letter language, DNA contains the information needed to build the entire human body. Traditionally, a gene refers to a unit of DNA that carries the instructions to make a specific protein or group of proteins. There are an estimated 20,000 to 25,000 genes in the human genome, each encoding an average of three proteins.

Located on 23 pairs of chromosomes inside the human cell nucleus, genes direct the production of proteins with the help of enzymes and messenger molecules. Specifically, enzymes copy information from a gene's DNA into a molecule called messenger ribonucleic acid (mRNA). The mRNA leaves the nucleus and enters the cytoplasm, where it is read by tiny molecular machines called ribosomes, and the information is used to link small molecules called amino acids together in the correct order to form specific proteins.

Proteins make up body structures such as organs and tissues, and control chemical reactions and transmit signals between cells. If a cell's DNA mutates, abnormal proteins can be produced, which can disrupt the body's normal processes and lead to diseases such as cancer.


- DNA Sequencing

Sequencing simply means determining the exact order of bases in a strand of DNA. Because base pairs exist in pairs, and the identity of one base determines the other base in the pair, researchers don't have to report both bases of the pair.

In the most common type of sequencing in use today, known as sequencing by synthesis, DNA polymerase (the enzyme in the cell that synthesizes DNA) is used to generate a new DNA strand from the strand of interest. In a sequencing reaction, an enzyme incorporates a single nucleotide, chemically tagged with a fluorescent tag, into a new strand of DNA. When this happens, the nucleotide is excited by the light source, and a fluorescent signal is emitted and detected. The signal differs depending on which of the four nucleotides is incorporated. This method can continuously generate "reads" of 125 nucleotides, and can generate billions of reads at a time.

To assemble the sequence of all the bases in a large stretch of DNA, such as a gene, researchers need to read the sequences of overlapping fragments. This allows longer sequences to be assembled from shorter pieces, a bit like putting together a linear puzzle. During this process, each base is read not only once, but at least multiple times in overlapping fragments to ensure accuracy.

Researchers can use DNA sequencing to look for genetic variations and/or mutations that may play a role in the development or progression of a disease. Disease-causing changes can be as small as a single base pair substitution, deletion or addition, or as large as a deletion of thousands of bases.

- Impact on Medicine

Virtually every human disease has something to do with our genes. Until recently, doctors have not been able to take the study of genes or genetics into account, only in the case of birth defects and a few other diseases. These diseases, like sickle cell anemia, have very simple, predictable patterns of inheritance because each disease is caused by changes in a single gene. 

Armed with vast amounts of data from genomic studies of human DNA production, scientists and clinicians have more powerful tools to study the role of multiple genetic factors working together, as well as with the environment, in more complex diseases. These diseases, such as cancer, diabetes, and cardiovascular disease, make up the bulk of America's health problems. Genome-based research has enabled medical researchers to develop improved diagnostics, more effective treatment strategies, evidence-based approaches to demonstrate clinical efficacy, and better decision-making tools for patients and providers. Ultimately, treatments will inevitably be tailored to a patient's specific genomic makeup. As a result, the role of genetics in healthcare begins to change profoundly, and the first examples of the era of genomic medicine are before us. 

However, it is important to realize that transferring a discovery from a scientific laboratory to a medical clinic often takes a significant amount of time, effort and money. Most new drugs based on genomic research are estimated to be at least 10 to 15 years away, although recent genome-driven lipid-lowering therapeutic efforts have shortened this time interval considerably. According to biotech experts, it typically takes more than a decade for a company to conduct the various clinical studies needed to gain Food and Drug Administration approval. 

Screening and diagnostic tests, however, are here to stay. Rapid progress has also been made in the emerging field of pharmacogenomics, which involves using information about a patient's genetic makeup to better tailor drug treatments to a patient's individual needs. 

Clearly, genetics is still only one of several factors that put people at risk for the most common diseases. Diet, lifestyle and environmental exposures also play a role in many conditions, including many types of cancer. Still, a deeper understanding of genetics will reveal more than just genetic risk by revealing the basic components of cells and, ultimately, how all the various elements work together to influence health and disease in the human body.


[More to come ...]


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