RNA vs DNA – the Differences

Nucleic acids such as deoxyribonucleic acid (DNA) and ribonucleic acid (RNA) are large biological molecules that are the foundation of life. Our genetic code comes from DNA. Mutations or damage to DNA contributes to serious complications in the genetic code.

Function

Not only are these molecules the basis for life, but they play a huge role in research, laboratory testing, and disease therapies. Many diseases are due to protein malfunction.

DNA, which can be found in the nucleus and mitochondria of human cells are molecules that bind together to form genes. Without these genes, our cells would never be able to produce proteins responsible for most biological functions within the body such as:

• metabolism
• reproduction
• cell signaling

Enzymes, hormones, and cell receptors are a few examples of proteins. These proteins are translated from messenger RNA (mRNA). RNA hanging out in the nucleus, cytoplasm, and ribosomes get synthesized from DNA.

Structure

Both, RNA and DNA have a sugar-phosphate backbone with nucleobases bound to it constructing the nucleotide. Without phosphate, the structure is called nucleoside. There are some important differences that make each macromolecule unique.

Stability is derived from a hydrogen bond instead of a hydroxyl bond that exists in ribose. The difference in sugar used in RNA vs DNA changes the function of each molecule. It’s amazing that what seems to be a small chemical change has such a vast impact.

RNA is a single-stranded molecule with four nucleobases: adenine that binds to uracil by means of a double hydrogen bond and cytosine binds with guanine via a triple hydrogen bond. Having the extra hydrogen bond provides extra strength making it more difficult to break.

Image Credit: thoughtco.com

DNA uses thymine that links with adenine in place of uracil. The binding of the nucleotides contributes to the shape of the nucleic acid. Slight changes in the RNA construct cause the molecule to fold on itself instead of forming shapes such as the famous double helix that DNA (using double strands) forms.

The helix consists of a complementary pairing of bases lined in the middle of the molecule with the sugar-phosphate backbone on the outside.

Stability

RNA is more abundant and has more varieties including mRNA, ribosomal RNA (rRNA), transfer RNA (tRNA), micro-RNA (miRNA), and small interfering RNA (siRNA). RNA also gets recycled often leading to high turnover.

The stability obtained in the deoxyribose is due to the C-H bond that the ribose sugar doesn’t have. Other factors play a role in nucleic acid stability. The hydrogen bonding that occurs with the nucleobase linkage increases stability.

Enzymes can degrade both RNA and DNA; however, RNA is more susceptible due to having more space in the molecule whereas the tightly formed helix doesn’t have as much room for enzyme attachment. In addition, RNA has been shown to degrade more so than DNA in the presence of alkaline solution.

Since RNA is created from DNA instead of being replicated in cells, it makes evolutionary sense that DNA is more stable.

Replication

In humans, genetic information is replicated during the cell cycle enabling growth. Cells form tissue that forms organs. Not only does the DNA replicate itself, but this same genetic information gets passed throughout generations.

When DNA replicates, the two stand separate so that a complementary strand can be produced. After the separation of strands, a primer (a short strand of nucleotides) is used along with an enzyme called DNA polymerase to create the new strand. RNA, in contrast, doesn’t get replicated but transcribed from DNA.

DNA is separated as it is in DNA replication, but DNA isn’t produced in the process of transcription. RNA polymerase creates a complementary RNA strand from the DNA that is being transcribed. mRNA that gets transcribed in this way then becomes translated into protein via the translation process.

Regulating these proteins determines how our cells function. Other types of RNA such as miRNAs and siRNAs aid in protein regulation. Utilizing unique pathways, both of these small RNA fragments target specific mRNA for degradation; therefore assisting in protein regulation.

Up to this point, nucleic acid contained in eukaryotic cells has been the main focus. Shifting gears slightly, other organisms have nucleic acids as well. Viruses consist of mostly DNA or RNA and require a host for their survival.

Using the host biology in addition to their own genetic material, viruses grow rapidly. In a similar manner as eukaryotic replication, DNA viruses generate mRNA that is converted to protein.

Replication of DNA viruses occurs in the nucleus of the host cell, whereas RNA viruses multiply in the cytoplasm. With RNA virus, no DNA exists to build mRNA; therefore, depending on the RNA virus, a variety of strategies have allowed for mRNA production that afterward becomes protein.

Like eukaryotic RNA, virus RNA is less stable than virus DNA making it more susceptible to mutation.

Genetic mutations

Genetic mutations increase the risk of disease and cell death. There are many reasons mutations emerge, nevertheless, a lot of focus is placed on induced mutagens such as radiation and chemical causing mutations.

Altered DNA doesn’t always lead to disease and cell death, but if the mutated DNA consequently modifies protein expression, disease and cell death are more likely.

Conclusion

Our knowledge has increased rapidly since the late 19^th century when nucleic acids were first discovered. Not only have we discovered how these molecules function, but we have taken that education to create a completely different world.

As of late, the emerging field of bioinformatics has enhanced discovery by obtaining more data at faster speeds than ever before.

We have come a long way from the days of Watson and Crick. There’s no telling what the future holds for us and generations to come.

References

1. Wikipedia: Nucleotide
2. Wikipedia: RNA world hypothesis
3. Wikipedia: DNA
4. Wikipedia: RNA
5. DNA Information – Genome.gov
6. RNA – Scitable