The Differences Between DNA and RNA

The Differences Between DNA and RNA Although their names may sound familiar, DNA and RNA are often confused for one another when there are in fact several key differences between these two carriers of genetic information.  Deoxyribonucleic acid  (DNA) and  ribonucleic acid  (RNA) both are made of nucleotides and serve a role in the production of protein and other parts of cells, but there are some key elements of both that differ on the nucleotide and base levels. Evolutionarily, scientists believe that RNA may have been the building block of early primitive organisms due to its simpler structure and its pivotal function of transcribing DNA sequences so that other parts of the cell may understand them- meaning RNA would have to exist in order for DNA to function, so it stands to reason RNA came first in the evolution of multi-celled organisms. Among these core differences between DNA and RNA is that RNAs backbone is made of a different sugar than DNAs, RNAs use of uracil instead of thymine in its nitrogenous base, and the number of strands on  each type of genetic information carriers molecules. Which Came First in Evolution? While there are arguments for DNA occurring naturally in the world first, it is generally agreed upon that RNA came before DNA for a variety of reasons, starting with its simpler structure and more easily interpretable codons which would allow for faster genetic evolution through reproduction and repetition. Many primitive prokaryotes use RNA as their genetic material and did not evolve DNA, and RNA can still be used as a catalyst for chemical reactions like enzymes. There are also clues, within viruses that use only RNA, that RNA may be more ancient than DNA, and scientists even refer to a time before DNA as the â€Å"RNA world. Then why did DNA evolve at all? This question is still being investigated, but one possible explanation is that DNA is more highly protected and harder to break down than RNA- it is both twisted and â€Å"zipped† up in a double-stranded molecule which adds protection from injury and digestion by enzymes. Primary Differences DNA and RNA are made up of subunits called nucleotides wherein all nucleotides have a sugar backbone, a phosphate group, and a nitrogenous base, and both DNA and RNA have sugar â€Å"backbones† that are made up of five carbon molecules; however, they are different sugars that make them up. DNA is made up of deoxyribose and RNA is made up of ribose, which may sound similar and have similar structures, but the deoxyribose sugar molecule is missing one oxygen that a ribose molecule sugar has, and this makes a big enough change to make the backbones of these nucleic acids different. The nitrogenous bases of RNA and DNA are also different, though in both these bases can be categorized into two main groups: the pyrimidines which have a single ring structure and purines which have a double ring structure. In both DNA and RNA, when complementary strands are made, a purine must match up with a pyrimidine to keep the width of the â€Å"ladder† at three rings. The purines in both RNA and DNA are called adenine and guanine, and they also both have a pyrimidine called cytosine; however, their second pyrimidine is different: DNA uses thymine while RNA includes uracil instead. When complementary strands are made of the genetic material, cytosine always matches up with guanine and adenine will match up with thymine (in DNA) or uracil (in RNA). This is called the â€Å"base pairing rules† and was discovered by Erwin Chargaff in the early 1950s. Another difference between DNA and RNA is the number of strands of the molecules. DNA is a double helix meaning it has two twisted strands that are complementary to each other match up by the base pairing rules while RNA, on the other hand, is only single-stranded and created in most eukaryotes by making a complementary strand to a single DNA strand. Comparison Chart for DNA and RNA Comparison DNA RNA Name DeoxyriboNucleic Acid RiboNucleic Acid Function Long-term storage of genetic information; transmission of genetic information to make other cells and new organisms. Used to transfer the genetic code from the nucleus to the ribosomes to make proteins. RNA is used to transmit genetic information in some organisms and may have been the molecule used to store genetic blueprints in primitive organisms. Structural Features B-form double helix. DNA is a double-stranded molecule consisting of a long chain of nucleotides. A-form helix. RNA usually is a single-strand helix consisting of shorter chains of nucleotides. Composition of Bases and Sugars deoxyribose sugarphosphate backboneadenine, guanine, cytosine, thymine bases ribose sugarphosphate backboneadenine, guanine, cytosine, uracil bases Propagation DNA is self-replicating. RNA is synthesized from DNA on an as-needed basis. Base Pairing AT (adenine-thymine)GC (guanine-cytosine) AU (adenine-uracil)GC (guanine-cytosine) Reactivity The C-H bonds in DNA make it fairly stable, plus the body destroys enzymes that would attack DNA. The small grooves in the helix also serve as protection, providing minimal space for enzymes to attach. The O-H bond in the ribose of RNA makes the molecule more reactive, compared with DNA. RNA is not stable under alkaline conditions, plus the large grooves in the molecule make it susceptible to enzyme attack. RNA is constantly produced, used, degraded, and recycled. Ultraviolet Damage DNA is susceptible to UV damage. Compared with DNA, RNA is relatively resistant to UV damage. The Differences Between DNA and RNA DNA stands for deoxyribonucleic acid, while RNA is ribonucleic acid. Although DNA and RNA both carry genetic information, there are quite a few differences between them. This is a comparison of the differences between DNA versus RNA, including a quick summary and a detailed table of the differences. Summary of Differences Between DNA and RNA DNA contains the sugar deoxyribose, while RNA contains the sugar ribose. The only difference between ribose and deoxyribose is that ribose has one more -OH group than deoxyribose, which has -H attached to the second (2) carbon in the ring.DNA is a double-stranded molecule while RNA is a single-stranded molecule.DNA is stable under alkaline conditions while RNA is not stable.DNA and RNA perform different functions in humans. DNA is responsible for storing and transferring genetic information while RNA directly codes for amino acids and as acts as a messenger between DNA and ribosomes to make proteins.DNA and RNA base pairing is slightly different since DNA uses the bases adenine, thymine, cytosine, and guanine; RNA uses adenine, uracil, cytosine, and guanine. Uracil differs from thymine in that it lacks a methyl group on its ring. Comparison of DNA and RNA While both DNA and RNA are used to store genetic information, there are clear differences between them. This table summarizes the key points: Comparison DNA RNA Name DeoxyriboNucleic Acid RiboNucleic Acid Function Long-term storage of genetic information; transmission of genetic information to make other cells and new organisms. Used to transfer the genetic code from the nucleus to the ribosomes to make proteins. RNA is used to transmit genetic information in some organisms and may have been the molecule used to store genetic blueprints in primitive organisms. Structural Features B-form double helix. DNA is a double-stranded molecule consisting of a long chain of nucleotides. A-form helix. RNA usually is a single-strand helix consisting of shorter chains of nucleotides. Composition of Bases and Sugars deoxyribose sugarphosphate backboneadenine, guanine, cytosine, thymine bases ribose sugarphosphate backboneadenine, guanine, cytosine, uracil bases Propagation DNA is self-replicating. RNA is synthesized from DNA on an as-needed basis. Base Pairing AT (adenine-thymine)GC (guanine-cytosine) AU (adenine-uracil)GC (guanine-cytosine) Reactivity The C-H bonds in DNA make it fairly stable, plus the body destroys enzymes that would attack DNA. The small grooves in the helix also serve as protection, providing minimal space for enzymes to attach. The O-H bond in the ribose of RNA makes the molecule more reactive, compared with DNA. RNA is not stable under alkaline conditions, plus the large grooves in the molecule make it susceptible to enzyme attack. RNA is constantly produced, used, degraded, and recycled. Ultraviolet Damage DNA is susceptible to UV damage. Compared with DNA, RNA is relatively resistant to UV damage. Which Came First? While there is some evidence DNA may have occurred first, most scientists believe RNA evolved before DNA. RNA has a simpler structure and is needed in order for DNA to function. Also, RNA is found in prokaryotes, which are believed to precede eukaryotes. RNA on its own can act as a catalyst for certain chemical reactions. The real question is why DNA evolved if RNA existed. The most likely answer for this is that having a double-stranded molecule helps protect the genetic code from damage. If one strand is broken, the other strand can serve as a template for repair. Proteins surrounding DNA also confer additional protection against enzymatic attack. Unusual DNA and RNA While the most common form of DNA is a double helix. there is evidence for rare cases of branched DNA, quadruplex DNA,  and molecules made from triple strands. Scientists have found DNA in which arsenic substitutes for phosphorus. Double-stranded RNA (dsRNA) sometimes occurs. It is similar to DNA, except thymine is replaced by uracil. This type of RNA is found in some viruses. When these viruses infect eukaryotic cells, the dsRNA can interfere with normal RNA function and stimulate an interferon response. Circular single strand RNA (circRNA) has been found in both animals and plants. At present, the function of this type of RNA is unknown. Sources Burge S, Parkinson GN, Hazel P, Todd AK, Neidle S (2006). Quadruplex DNA: sequence, topology and structure. Nucleic Acids Research. 34 (19): 5402–15. doi:10.1093/nar/gkl655Whitehead KA, Dahlman JE, Langer RS, Anderson DG (2011). Silencing or stimulation? siRNA delivery and the immune system. Annual Review of Chemical and Biomolecular Engineering. 2: 77–96. doi:10.1146/annurev-chembioeng-061010-114133