Beyond The Central Dogma

Beyond The Central Dogma

The principal dogma of molecular biology explains that DNA codes for RNA, which codes for proteins. Within the crucial Dogma, you can find out about the vital roles of messenger RNA, switch RNA and ribosomal RNA within the protein-building method. However, RNA does more than just construct proteins. RNA has many roles inside the cellular, including jobs that have been traditionally associated with DNA and proteins. Continue reading to learn about how RNA can deliver hereditary information, act as enzymes, and fine-tune protein production. Additionally, discover how advances in RNA technology are assisting researchers in studying genes, diagnosing, and treating diseases.

RNA Can Carry Genetic Information

Most organisms use DNA to store genetic information. The DNA is passed from parents to offspring over generations. However, some viruses, such as HIV, the virus that causes AIDS, use RNA to store genetic information. These RNA viruses are referred to as retroviruses. RNA has a form similar to DNA’s; in both molecules, the sequence of bases can code for proteins. RNA was likely the molecule of heredity in some of the earliest life forms (Kawaji, 2008).

RNA Can Build and Break Molecules

Enzymes are catalysts: they build and break down molecules at a rate rapid enough to sustain life. Scientists once believed that all enzymes within the cell were proteins. Then it was discovered that some RNA molecules can also be enzymes. These so-called ribozymes are rare, but they play key roles within the cell. In the ribosome, RNA joins amino acids together, allowing cells to construct proteins. Some mRNA molecules contain self-splicing introns that can break and rejoin the mRNA strand. A ribozyme in the RNAse P complex activates tRNA molecules by clipping off their ends (Kawaji, 2008). Ribozymes provide further evidence that RNA may have been the first molecule of life. In a primitive life form, RNA may have both catalyzed chemical reactions and stored genetic information, functions later taken over by DNA and proteins.

RNA Can Silence Genes

Some RNA molecules can silence specific genes, turning off the production of proteins that aren’t needed at a certain location or time. This process is particularly important during development when cells begin to differentiate into specific types, such as muscle, skin, and liver. Each cell type needs only a fraction of its total genes to be active to perform its function. Gene-silencing RNA molecules recognize specific genetic sequences through complementary base-pairing. These RNA molecules can shut down portions of the genome, turning off protein production. RNA achieves this by recruiting proteins to regulate histones (or the epigenome). Modified histones wrap DNA tightly, making it inaccessible to transcription machinery. Scientists first build a small RNA molecule with a nucleotide sequence that matches a specific gene. By observing what happens as the organism develops without the gene, scientists gain insights into the gene’s natural function (Wapinsky & Chang, 2011).

RNA Protects the Genome

Some RNAs silence harmful DNA sequences that reside in our genomes as relics of our evolutionary past. Transposons (“jumping genes”) and the genes of infecting viruses made their way into our ancestors' DNA, and they continue to be passed from parent to offspring. RNAs inactivate viral genes and transposons, preventing them from causing harm.

RNA Can Fine-Tune Protein Production

A variety of RNA molecules assist the cell in fine-tuning when, where, and how much of a particular mRNA molecule, and by extension a specific protein, is made. Regulatory RNAs can act at almost every step of the protein-production process. Some RNAs (referred to as riboregulators) bind DNA switches to turn genes on and off. Others interact directly with mRNA molecules to regulate splicing, protect mRNA from damage, or degrade it into pieces.

RNA Responds to the Environment

Riboswitches help some cells respond to external signals, typically small molecules. Riboswitches are found on larger mRNA molecules, and they fold into intricate shapes. When the small molecule—such as a metal ion, amino acid, or nucleic acid—binds to the riboswitch, it causes the RNA's shape to change. The shape change affects whether the mRNA is translated into protein. In bacteria, riboswitches regulate mRNAs that code for proteins involved in metabolic pathways. The small molecule that triggers the riboswitch is usually part of the same pathway. Thus, the riboswitch provides feedback to the pathway (Wapinsky & Chang, 2011).

RNA Therapies and Diagnostics

Scientists are designing RNA molecules and using them as tools to diagnose and even treat illnesses, including cancer, diabetes, arthritis, heart disease, brain diseases, and viral infections. Scientists can easily design RNA molecules to attach to a specific nucleotide sequence in a gene or mRNA molecule. These RNA molecules could potentially be used in the future to inactivate a faulty disease gene. As a diagnostic tool, RNA molecules can be engineered to identify certain substances in the blood that are present only with a specific disease. Misbehaving RNA molecules can also cause diseases, such as Alzheimer’s and other neurodegenerative diseases. The more we learn about RNA’s role in these diseases, the better equipped we will be to treat them.

References:

• Kawaji, H. (2008). RNA: The First Molecule of Life. Journal of Molecular Biology.
• Wapinsky, O., & Chang, H.Y. (2011). Riboswitches: Regulators of Gene Expression. Nature Reviews Molecular Cell Biology.