RNA
RNA or ribonucleic acid, is made up of a series of nucleotides joined by 3'-5' phosphodiester bonds. RNA forms a polynucleotide strand with a sugar-phosphate backbone. The phosphodiester bonds that make up the backbone have a negative charge, which protects the molecule from being hydrolysed by nucleophilic attack as the negative charges of the backbone and nucleophile repel each other.
RNA differs from DNA as it has a ribose sugar, whereas DNA has a deoxyribose sugar, the ribose sugar contains a 2` hydroxyl group. Like DNA, four nucleotide bases: cytosine (C), guanine (G), adenine (A) and uracil (DNA has a thymine base rather than uracil) are attached to the backbone. In RNA, C pairs with G, but A pairs with 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
- Single polynucleotide strand made in the nucleus during transcription
- DNA is transcribed into mRNA by an RNA polymerase, 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)
- The short-lived, unprocessed or partially processed product is termed precursor mRNA, or pre-mRNA; once completely processed, it is termed mature mRNA
- In bacterial organisms like E. coli the mRNA is polycistronic, whereas in most eukaryotic organisms the mRNA only codes for one gene (monocistronic).[4]
- Single polynucleotide strand which is folded into three hairpinloops which gives it a clover leaf structure, held together by hydrogen bonds
- Consists of a specific sequence of three unpairedbases 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.
- It is typically 76 to 90 nucleotides in length
- This is the RNAwhich forms ribosomes
- It acts as a catalyst for protein synthesis
- It is synthesised in the nucleolus
- rRNA molecules do not code for protein
- tRNA has two subunits: large subunit (LSU) and small subunit (SSU). Large subunit acts as ribozymes which catalyse peptide bond formation. In animals the size of the large subunit is 60s and 20s of the small subunit thus ribosome is 80s overall in Eukaryotes.
- It is used to work out evoutionary patterns between species since they are all form of lifes.
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.
4. snRNA - small nuclear RNA[7]
- commonly known as U-RNA
- function in various nuclear processes
- function in the splicing of pre-mRNA
- transcribed by either RNA polymerase II or RNA polymerase III
5. snoRNA - small nucleolar RNA[8]
- used to process and modify rRNA chemically
6. scaRNA - small cajal RNA[9]
- a class of snoRNAs
- locate at the Cajal body
- to modify snoRNA and snRNA
7. miRNA - microRNA[10]
- non-coding RNA molecule
- containing approximately 22 nucleotides
- regulate gene expression by blocking translation of selective mRNA
8. siRNA - small interfering RNA[11]
- also known as silencing RNA
- double stranded RNA molecules
- turn off gene expression by directing degradation of selective mRNA and the establishment of compact chromatin structures
RNA can also exist in non coding forms. These non-coding RNAs function in diverse cell processes, such as telomere synthesis, transport of proteins into the endoplasmic recticulum and X-chromosome inactivation[12]. Beasides, non-coding RNAs also 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[13].
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
- ↑ https://en.wikipedia.org/wiki/Messenger_RNA
- ↑ 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. Page 336
- ↑ Alberts, B., Johnson, A., Lewis, J., Raff, M.,Roberts, K., Walter, P. (2008). Molecular Biology of The Cell 5th edition. New York: Garland Science. Page 336
- ↑ Alberts, B., Johnson, A., Lewis, J., Raff, M.,Roberts, K., Walter, P. (2008). Molecular Biology of The Cell 5th edition. New York: Garland Science. Page 336
- ↑ Alberts, B., Johnson, A., Lewis, J., Raff, M.,Roberts, K., Walter, P. (2008). Molecular Biology of The Cell 5th edition. New York: Garland Science. Page 336
- ↑ Alberts, B., Johnson, A., Lewis, J., Raff, M.,Roberts, K., Walter, P. (2008). Molecular Biology of The Cell 5th edition. New York: Garland Science. Page 336
- ↑ Alberts, B., Johnson, A., Lewis, J., Raff, M.,Roberts, K., Walter, P. (2008). Molecular Biology of The Cell 5th edition. New York: Garland Science. Page 336
- ↑ 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