Ribonucleic acid or RNA is a nucleic acid found in all living cells. While RNA resembles DNA in many ways, it contains a different set of bases, usually is single-stranded instead of double-stranded, and transcribes DNA so a cell can make proteins. Like DNA, RNA molecules consist of a backbone of alternating phosphate and sugar groups. However, the sugar in RNA is ribose, while the one in DNA is 2′-deoxyribose. Each sugar attaches to one of four bases. In DNA, these bases are adenine, thymine, guanine, and cytosine. RNA uses uracil instead of thymine. Many cells contain both DNA and RNA, but some viruses only contain RNA.
- RNA stands for ribonucleic acid.
- RNA serves many purposes, including transcription and translation.
- Transcription is making RNA from a DNA template.
- Translation involves taking this RNA and making proteins.
Two of the most familiar functions of RNA are transcription and translation, but it is a key to many important activities in cells.
- RNA is the principal genetic material in some viruses.
- In transcription, a cell makes RNA from DNA.
- RNA interference controls the post-transcription of some genes by targeting regions of the genetic code for degradation.
- In translation, cells take this RNA and make proteins. Every three nucleotides is a codon for one amino acid. Chains of amino acids make polypeptides, which in turn make proteins.
- RNA is responsible for some post-translational modifications of proteins.
- RNA regulates genes, sometimes enhancing gene expression and sometimes repressing it.
Types of RNA
There are dozens of types of RNA. The best-studied forms are involved in protein synthesis, DNA replications, post-transcriptional modification, and gene regulation. Three important types of RNA that are found in all living organisms are messenger RNA, ribosomal RNA, and transfer RNA.
- mRNA or messenger RNA: mRNA is a single-stranded molecule that codes for proteins. It forms during transcription. In eukaryotic cells, mRNA is the RNA version of a DNA genetic blueprint that carries the genetic code from the nucleus into the cytoplasm.
- rRNA or ribosomal RNA: rRNA translates proteins. rRNA is a non-coding form of RNA that makes up most of a ribosome. It manages the interaction between mRNA and tRNA that translates the code from mRNA into proteins. While mRNA is a single-stranded molecule, rRNA is large, complex, and consists of subunits.
- tRNA or transfer RNA: tRNA is a relatively small RNA molecule (76 to 90 nucleotides) that acts as the link between mRNA and the rRNA that makes proteins. The molecule has a cloverleaf structure, which includes loops and double-stranded sections.
Friedrich Miescher discovered nucleic acids in the nuclei of eukaryotic cells in1868. Later, scientists realized prokaryotic cells also contain nucleic acids. By 1939, researchers suspected RNA played a role in protein synthesis. Severo Ochoa won half of the 1959 Novel Prize in Medicine for his discovery of an enzyme capable of synthesizing RNA (although later that enzyme was shown to cause RNA degradation rather than synthesis). In 1956, David Davies and Alex Rich made a crystal of RNA so that x-ray crystallography could reveal its structure. In 1965, Robert W. Holley sequenced yeast rRNA, earning him a third of the 1968 Nobel Prize in Medicine.
In the 1970s, scientists discovered enzymes could make DNA from RNA (the opposite of transcription). In 2022, researchers found that RNA spontaneously forms on prebiotic basalt lava. This discovery supports Carl Woese’s 1968 hypothesis that the earliest forms of life used RNA to code genetic information, make proteins, and regulate biochemical reactions.
RNA research remains an interesting field of research. Scientists continue discovering new functions of this important molecule.
Interesting RNA Facts
- Cells contain much more RNA than DNA. For example, RNA accounts for about 5% of the weight of a human cell, while DNA only accounts for about 1% of its weight.
- In human cells, DNA only occurs within the nucleus, but RNA occurs in both the cytoplasm and nucleus.
- Some cancer treatments use RNA because of its ability to reduce expression of cancer-causing genes.
- RNA can suppress fruit ripening, keeping food fresh longer so it can be transported to stores.
- Adenine binds to uracil in RNA rather than thymine as in DNA. Uracil is simply an unmethylated form of thymine.
- While most RNA is single-stranded, there is also double-stranded and circular RNA.
- Some times of RNA are parasitic. Viruses and viroids use RNA to make infected cells propagate their code.
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