RNA
RNA stands for ribonucleic acid. It is made up of a series of nucleotides joined by 3'-5' phosphodiester bonds. RNA forms a polynucleotide strand with a sugar-phosphate backbone. Unlike DNA, RNA has a ribose sugar, which means that it has a 2` hydroxyl group.
Attached to the backbone are 4 bases, in a similar way to DNA, in which cytosine (C) pairs with guanine (G) and thymine (T) pairs with adenine (A). However in RNA C pairs with G, but A pairs with uracil (U) instead of T [1]. RNA is typically single-stranded, although regions can form where the RNA loops back on itself, to produce "hairpin" secondary structures.[2]
RNA involved in gene expression
1. mRNA – messenger RNA [3]
- Single polynucleotide strand made in the nucleus during transcription
- DNA is transcribed into mRNA, therefore the mRNA and the DNA are complementary
- mRNA carries the genetic code from the DNA in the nucleus to the ribosomes in the cytoplasm
- This mRNA is then used as a template for translation into a functional protein
- mRNA is also used to make copy DNA (cDNA)
- Single polynucleotide strand which is folded into a clover shape, held together by hydrogen bonds
- Consists of a specific sequence of three unpaired bases bound to a complementary codon (anticodon) and an amino acid binding site
- Found in the cytoplasm, where it is involved in translation
- This molecule carries amino acids to the ribosomes where a polypeptide is formed, the sequence of which was determined by the mRNA.
3. rRNA – ribosomal RNA [5]
- This is the RNA which forms ribosomes
- It acts as a catalyst for protein synthesis
- It is synthesised in the nucleolus
- rRNA molecules do not code for protein
The three RNAs all work together to convert the initial DNA molecule into a protein. All three of these types of RNA are synthesised by RNA Polymerase.
RNA can also exist in non coding forms. These non-coding RNAs have many applications but many revolve around regulation of gene expression, such as riboswitches in bacteria and miRNAs involved in RNAi (RNA interference) in animals [6].
References
- ↑ Berg JM, Tymoczko JL and Stryer L, 2007, Biochemistry 6th edition, NY, W. H Freeman and Company, page 109
- ↑ Lyons, I, 2011. Biomedical Science Lecture Notes. 1st ed. Oxford: Wiley-Blackwell, p21-23
- ↑ Berg JM, Tymoczko JL and Stryer L, 2007, Biochemistry 6th edition, NY, W. H Freeman and Company, page 119
- ↑ Berg JM, Tymoczko JL and Stryer L, 2007, Biochemistry 6th edition, NY, W. H Freeman and Company, page 120
- ↑ Berg JM, Tymoczko JL and Stryer L, 2007, Biochemistry 6th edition, NY, W. H Freeman and Company, page 120
- ↑ Alberts B, Johnson A, Lewis J, Raff M, Roberts K, Walter P,2008, Molecular Biology of the Cell,5th Edition, New York, Garland Science, pg 493