The 7 differences between DNA and RNA

Differences between DNA and RNA: composition

Both RNA and DNA are molecules made up of two main components: a sugar backbone and small modularly arranged compounds, nucleotides , also known as nitrogenous bases.

In this section we will discuss some of the fundamental biochemical differences between these molecules.

1. Differences in the sugar backbone

The difference at this level is simple, but so fundamental that it determines the names of both molecules. DNA, in English DNA, is an acronym for “deoxyribonucleic acid”. On the other hand, RNA, in English RNA, is an acronym for “ribonucleic acid” . In simple terms, this means that RNA has one extra oxygen molecule relative to DNA (hence the “deoxy-” particle in DNA’s name, indicating that it has one less oxygen).

This difference gives DNA greater stability compared to RNA , which makes sense from a biological perspective, since it is in the interest of DNA to change as little as possible to keep the instructions for which it encodes intact.

2. Differences in nitrogenous bases

The small molecules arranged along the sugar backbone are called nucleotides. If the skeleton of sugars were a book, the nucleotides would be the letters in which our genetic code is written . In nature we find 5 different types, whose names are simplified into letters to facilitate our reading of DNA and RNA chains: Adenine (A), Cytosine (C), Guanine (G), Thymine (T) and Uracil (U) .

In DNA we will only find A, C, G and T. However, RNA will not present Thymine in its structure and it is replaced by Uracil. This facilitates the identification of the molecules, since we will not find Thymine in an RNA sample or Uracil in a DNA sample, and this distinction has various biochemical and functional consequences for both molecules.

3. Structural differences

The representation of DNA that we have all seen is that of a helix, made up of two DNA molecules joined in a complementary way . Each base, under normal conditions, will only bind with its opposite base (Adenine with Thymine, Guanine with Cytosine). This gives us two DNA strands with complementary information, that is, by reading one strand we would be able to extrapolate the information from the complementary strand.

DNA is usually structured following this double-stranded structure. RNA, on the other hand, is not usually found in a double-molecule structure (that is, bound to another complementary RNA molecule) even though it has the ability to do so. In these cases, or when the RNA is bound to DNA, the Uracil will be complementary to the Adenine, following the function that the Thymine would have.

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functional differences

To talk about the functional differences between these molecules, we must put into context the importance of DNA for life as a concept. Living structures are extremely complex and tend to degenerate over time . This problem is somewhat circumvented if the instructions for forming another living organism are passed along, along with the machinery needed to form it.

This is where the importance of DNA comes in. Being the instructions we are talking about, it is necessary that the instructions remain as close to the original as possible . Any change in the instructions is what we call a mutation , a variation in the DNA sequence that can completely change the meaning that our molecule encodes.

The characteristics of DNA are influenced by the task it performs: It is necessary for the DNA to be as protected as possible, to minimize the risk of mutations , while allowing its interaction with the cellular environment to be able to read the instructions that it contains. encode. RNA, on the other hand, is a molecule with more varied functions, which does not need to be so highly protected.

The best known function of RNA is that of the so-called messenger RNA. This type of RNA is a copy of a DNA molecule, as if we were making a photocopy of a book that we cannot take out of the library . The cell uses this photocopy to read the information encoded in DNA without the need to expose it to the cellular environment.

The RNA in our cells is constantly being created and degraded and its functions go beyond being a simple intermediate step between the information of the DNA and the proteins for which it codes. The functions of RNA will vary depending on how we find it structured and to which elements it is bound.

The different functions of these molecules give rise to:

1. Differences in location

We will see that DNA is usually found in environments protected from the rest of the cell, such as the cell nucleus or inside the mitochondria (where the so-called mitochondrial DNA is found, of exclusively maternal origin). We will also find RNA in these environments, but it is common to find it performing different functions in the rest of the cell.

An example of this would be the ribosomes, hybrid structures formed by RNA and proteins, whose function is to synthesize proteins from the instructions read in simple RNA chains. These ribosomes are usually found attached to the endoplasmic reticulum, or floating in the cell cytoplasm.

2. Differences in grouping

DNA consists of longer chains, condensed in the areas we discussed earlier. This is achieved by binding the DNA to proteins that facilitate its packaging, such as the so-called histones. Thanks to protein binding and complicated packaging maneuvers, we can get the approximately two meters long that our genetic code is to fit together in about 6 micrometers .

RNA, on the other hand, is found in shorter length chains, bound to proteins that affect its final function and in a constant state of renewal. The half-life of a messenger RNA molecule is about 30 minutes in eukaryotes , living things that have a nucleus. The half-life of RNA in the cell will vary according to its function, morphology and the proteins with which it is associated.

3. Differences in stability

The cell is full of enzymes that are responsible for breaking down genetic material . In addition to regulating RNA levels, this also functions as a defense system to prevent foreign genetic material from entering the cell (such as that which comes from viruses, which inject their genetic material into cells so that they replicate it for them, which they lack the necessary machinery to replicate their genetic material).

Furthermore, the simple RNA molecule is more exposed to interactions with elements that could affect its code if we compare it with the double DNA molecule, whose nucleotides are found on the inside of the molecule, conferring greater stability and less reactivity. than that of RNA.

RNA, on the other hand, is a clear winner in one category of stability: its resistance against ultraviolet light. Ultraviolet radiation affects DNA to a greater extent, which will have a tendency to accumulate damage such as pyrimidine dimers , when two nucleotides such as Thymine and another Thymine join together, which should not be. These damages must be repaired by the cellular machinery, since they damage the structure and the message of the DNA molecule.

conclusion

The differences between these molecules are diverse and, as we investigate the subject, we will realize that these differences have to do with their biochemical characteristics and the functions they perform in the cell. This article tries to present in a simple way some differences of these molecules, but they are not the only ones .

We hope that this article has managed to satisfy a little your curiosity about these fascinating molecules.

• If you want to know more about genetics: “Molecular genetics: what is it and in what fields can it be applied?”

Bibliographic references

• What is DNA? (2019) Retrieved from https://ghr.nlm.nih.gov/primer/basics/dna on 06/10/2019.
• Wil Prall, et al. (2019) Transcription Is Just the Beginning of Gene Expression Regulation: The Functional Significance of RNA-Binding Proteins to Post-transcriptional Processes in Plants, Plant and Cell Physiology.