The Carriers of Genetic Information in Cell Reproduction

The differences between RNA and DNA

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 RNA's backbone is made of a different sugar than DNA's, RNA's use of uracil instead of thymine in its nitrogenous base, and the number of strands on each type of genetic information carrier's 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 “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 “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 “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 “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 “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 sugar
phosphate backbone
adenine, guanine, cytosine, thymine bases
ribose sugar
phosphate backbone
adenine, 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.