What are you going to learn?

  • What is the difference between RNA and DNA?
  • What are the different types of RNA molecules?
  • What is the function of mRNA, tRNA, and rRNA?
  • terms: pre-mRNA, snRNAs, snRNPs, anticodon

Like DNA, RNA (ribonucleic acid) also consists of 3 basic components:
1) a phosphate group,
2) a five-carbon sugar,
3) a cyclic nitrogen-containing compound called a base.

In RNA, however, the five-carbon sugar is ribose, hence the name ribonucleic acid.  The difference between 2-deoxyribose found in DNA and ribose is that ribose has an -OH group on its 2'-carbon, whereas deoxyribose only an H atom.

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In RNA, the five carbon sugar is ribose, which has an -OH group on its 2'-carbon.

What is more, the bases in RNA differ from DNA as there is uracil instead of thymine. Uracil is a pyrimidine just like thymine. The following base-pairing rules apply: adenine pairs with uracil and guanine pairs with cytosine.

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In RNA, there is uracil instead of thymine (found in DNA).

While DNA is double-stranded, RNA is usually single-stranded (with some exceptions). However, short segments of RNA can pair and form different secondary structures.

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RNA is usually single-stranded.

mRNA

Messenger RNA is the product of transcription, the process in which the DNA code is rewritten into an RNA molecule. mRNA that can be used for translation must, however, first undergo post-transcriptional processing, before that, the molecule is referred to as pre-mRNA.

tRNA

Transfer RNA is a molecule that brings amino acids to the ribosome during translation, the process in which a protein is synthesized based on the rewritten information in mRNA. tRNA has a specific structure because it contains four short double-helical segments making the molecule look like a cloverleaf. Two of these regions are important: 1) anticodon, three nucleotides that bind (through base-pairing) to a complementary codon in the mRNA molecule to ensure that a correct amino acid is added to the protein; 2) amino-acid-accepting arm, where the amino acid gets attached to the tRNA.

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tRNAs transfer amino acids to the ribosome.
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tRNA's structure:
1) anticodon - binds to a complementary codon
2) amino-acid-accepting arm - contains the attached amino acid

rRNA

Ribosomal RNA forms the ribosome together with other proteins. It is very important for translation to function properly.

Other RNA molecules

Besides mRNA, tRNA, and rRNA, there are also other RNA molecules, for example small nuclear RNAs (snRNAs) that are responsible for RNA splicing during transcription together with proteins called small nuclear ribonucleoproteins (snRNPs, "snurps").

MicroRNA (miRNA), small interfering RNA (siRNA) and other RNA molecules will also be mentioned in other articles.

References:
Alberts, B. (2014). Essential Cell Biology. Garland Science.
Pierce, B. A. (2019). Genetics: A Conceptual Approach (Seventh ed.). W. H. Freeman.
Snustad, D. P., & Simmons, M. J. (2012). Principles of Genetics. Wiley