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RNA stands for ribonucleic acid. It is made up of a series of [[Nucleotides|nucleotides]] joined by 3'-5'[[Phosphodiester|phosphodiester]] bonds. RNAforms a polynucleotide strand with a sugar-phosphate backbone. Unlike [[DNA]], RNA has a [[Ribose|ribose]] sugar, which means that it has a 2` [[Hydroxyl group|hydroxyl group]]. The phosphodiester bonds that make up the backbone have a negative charge, this ensures it cannot be hydrolysed by nucleophilic attack, for example by hydroxide ions, as the negative charges repel each other.<ref>Berg, J.M., Tymoczko, J.L., and Stryer, L. (2011). Biochemistry. 7th ed. New York: W. H. Freeman and Company. 115.</ref>
RNA or [[Ribonuceic acid|ribonucleic acid]], is made up of a series of [[Nucleotides|nucleotides]] joined by 3'-5' [[Phosphodiester|phosphodiester]] bonds. RNA forms a polynucleotide strand with a sugar-phosphate backbone. The phosphodiester bonds that makes up the backbone has a negative charge, which protects the molecule from being hydrolyzed by a nucleophilic attack as the negative charges of the backbone and [[Nucleophile|nucleophile repel]] each other.  


Attached to the backbone are 4 [[Base|bases]], in a similar way to DNA, in which[[Cytosine|cytosine]] (C) pairs with [[Guanine|guanine]] (G) and [[Thymine|thymine]] (T) pairs with [[Adenine|adenine]] (A). However in RNAC pairs with G, but A pairs with [[Uracil|uracil]] (U) instead of T<ref>Berg JM, Tymoczko JL and Stryer L, 2007, Biochemistry 6th edition, NY, W. H Freeman and Company, page 109</ref>. RNA is typically single-stranded, although regions can form where the RNA loops back on itself, to produce "[[Hairpin|hairpin]]"secondary structures.<ref name="null">Lyons, I, 2011. Biomedical Science Lecture Notes. 1st ed. Oxford: Wiley-Blackwell, p21-23</ref>  
RNA differs from [[DNA|DNA]]&nbsp;as it has a [[Ribose|ribose]] sugar, whereas DNA has a deoxyribose sugar. The ribose sugar contains a 2` [[Hydroxyl group|hydroxyl group]]&nbsp;and DNA contains a 3' hydroxyl group. Like DNA, RNA has&nbsp;four nucleotide [[Base|bases]]: [[Cytosine|cytosine]] (C), [[Guanine|guanine]] (G), [[Adenine|adenine ]](A) and [[Uracil|uracil ]](DNA has a [[Thymine|thymine]] base rather than [[Uracil|uracil]]) that are attached to the backbone. In RNA, C pairs with G, but A pairs with U instead of T<ref>Berg JM, Tymoczko JL and Stryer L, 2007, Biochemistry 6th edition, NY, W. H Freeman and Company, page 109</ref>. RNA is typically single-stranded, although regions can form where the RNA loops back on itself, to produce "[[Hairpin|hairpin]]" secondary structures<ref name="null">Lyons, I, 2011. Biomedical Science Lecture Notes. 1st ed. Oxford: Wiley-Blackwell, p21-23</ref>, an example of this is in the termination step of transcription.


== RNA involved in gene expression  ==
== RNA involved in gene expression  ==


1. [[MRNA|mRNA]] – messenger RNA <ref>Berg JM, Tymoczko JL and Stryer L, 2007, Biochemistry 6th edition, NY, W. H Freeman and Company, page 119</ref>  
=== 1. [[MRNA|mRNA]] – messenger RNA<ref>Berg JM, Tymoczko JL and Stryer L, 2007, Biochemistry 6th edition, NY, W. H Freeman and Company, page 119</ref> ===


**Single polynucleotide strand madein the nucleus during [[Transcription|transcription]]  
*Single polynucleotide strand made in the nucleus during [[Transcription|transcription]]  
**DNA is transcribed into mRNA, therefore the mRNA and the DNA are complementary  
*DNA is transcribed into mRNA by an RNA polymerase, therefore the mRNA and the DNA are complementary  
**mRNA carries the [[Genetic code|genetic code]] from the DNA in the nucleus to the [[Ribosomes|ribosomes]] in the [[Cytoplasm|cytoplasm]]<br>** This mRNAis then used as a template for [[Translation|translation]] into a functional protein<br>** mRNAis also used to make copy DNA([[CDNA|cDNA]])
*mRNA carries the [[Genetic code|genetic code]] from the DNA in the nucleus to the [[Ribosomes|ribosomes]] in the [[Cytoplasm|cytoplasm]]  
*This mRNA is then used as a template for [[Translation|translation]] into a functional protein  
*mRNA is also used to make copy DNA([[CDNA|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 [[Eukaryote|eukaryotic]] organisms the mRNA only codes for one [[Gene|gene]] (monocistronic).<ref>https://en.wikipedia.org/wiki/Messenger_RNA</ref>


2. [[TRNA|tRNA]] – transfer RNA<ref>Berg JM, Tymoczko JL and Stryer L, 2007, Biochemistry 6th edition, NY, W. H Freeman and Company, page 120</ref>  
=== 2. [[TRNA|tRNA]] – transfer RNA<ref>Berg JM, Tymoczko JL and Stryer L, 2007, Biochemistry 6th edition, NY, W. H Freeman and Company, page 120</ref> ===


**Single polynucleotide strand whichis folded into a clover shape, held together by [[Hydrogen bonds|hydrogen bonds]]<br>** Consists of a specificsequence of three unpairedbases boundto a complementary [[Codon|codon]]([[Anticodon|anticodon]])and an[[Amino acid|amino acid]] bindingsite
*Single polynucleotide strand which is folded into three hairpin-loops which gives it a cloverleaf structure, held together by [[Hydrogen bonds|hydrogen bonds]]  
**Found in the [[Cytoplasm|cytoplasm]], where it is involved in translation  
*Consists of a specific sequence of three unpaired bases bound to a complementary [[Codon|codon]] ([[Anticodon|anticodon]]) and an [[Amino acid|amino acid]] binding site
**This [[Molecule|moleculecarriesamino]] acids tothe ribosomes where a [[Polypeptide|polypeptide]] is formed, the sequence of which was determined by the [[MRNA|mRNA]].
*Found in the [[Cytoplasm|cytoplasm]], where it is involved in translation  
*This [[Molecule|molecule]] carries amino acids to the ribosomes where a [[Polypeptide|polypeptide]] is formed, the sequence of which was determined by the [[MRNA|mRNA]].  
*It is typically 76 to 90 nucleotides in length


3. [[RRNA|rRNA]] – ribosomal RNA<ref>Berg JM, Tymoczko JL and Stryer L, 2007, Biochemistry 6th edition, NY, W. H Freeman and Company, page 120</ref>  
=== 3. [[RRNA|rRNA]] – ribosomal RNA<ref>Berg JM, Tymoczko JL and Stryer L, 2007, Biochemistry 6th edition, NY, W. H Freeman and Company, page 120</ref> ===


**This is the RNAwhich forms[[Ribosomes|ribosomes]]  
*This is the RNA which forms [[Ribosomes|ribosomes]]  
**It acts as a catalyst for [[Proteins|protein]] synthesis  
*It acts as a catalyst for [[Proteins|protein]] synthesis  
**It is synthesised in the [[Nucleolus|nucleolus]]
*It is synthesized in the [[Nucleolus|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 evolutionary patterns between species since they are all form of life.


- rRNA molecules do not code for protein<br>
The three RNAs all work together to convert the initial DNA molecule into a protein. All three of these types of RNA are synthesized by RNA Polymerase.


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.<br>  
=== 4. snRNA - small nuclear RNA<ref>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</ref> ===


4. snRNA - small nuclear RNA<ref>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</ref>
*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


**commonly known as U-RNA  
=== 5. snoRNA - small nucleolar RNA<ref>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</ref>  ===
**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<ref>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</ref>
*used to process and modify rRNA chemically


**used to process and modify rRNA chemically
=== 6. scaRNA - small cajal RNA<ref>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</ref>  ===


6. scaRNA - small cajal RNA<ref>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</ref>
*a class of snoRNAs
*locate at the Cajal body
*to modify snoRNA and snRNA


**a class of snoRNAs
=== 7. miRNA - microRNA<ref>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</ref>  ===
**locate at the Cajal body
**to modify snoRNA and snRNA


7. miRNA - microRNA<ref>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</ref>
*non-coding RNA molecule
*containing approximately 22 nucleotides
*regulate gene expression by blocking translation of selective mRNA


**non-coding RNA molecule
=== 8. siRNA - small interfering RNA<ref>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</ref>  ===
**containing approximately 22 nucleotides
**regulate gene expression by blocking translation of selective mRNA


8. siRNA - small interfering RNA<ref>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</ref>
*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


**also known as silencing RNA
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 reticulum and X-chromosome inactivation<ref>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</ref>. Besides, non-coding RNAs also have many applications but many revolve around regulation of [[Gene|gene]] expression, such as [[Riboswitches|riboswitches]] in bacteria and miRNAs involved in [[RNAi]] (RNA interference) in animals<ref>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</ref>.  
**double stranded RNA molecules
**turn off gene expression by directing degradation of selective mRNA and the establishment of compact chromatin structures<br>
 
RNA can also exist in non coding forms. These non-coding RNAs function in diverse cell processes, such as telomere synthesis, transport of proteins intot the endoplasmic recticulum and X-chromosome inactivation<ref>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</ref>. Beasides, non-coding RNAs also have many applications but many revolve around regulation of [[Gene|gene]] expression, such as [[Riboswitches|riboswitchesin]] bacteria and miRNAs involved in [[RNAi]](RNA interference) in animals<ref>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</ref>.  


== References  ==
== References  ==


<references />
<references />

Latest revision as of 12:17, 5 December 2017

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 makes up the backbone has a negative charge, which protects the molecule from being hydrolyzed by a 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 and DNA contains a 3' hydroxyl group. Like DNA, RNA has four nucleotide bases: cytosine (C), guanine (G), adenine (A) and uracil (DNA has a thymine base rather than uracil) that 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], an example of this is in the termination step of transcription.

RNA involved in gene expression

1. mRNA – messenger RNA[3]

  • 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]

2. tRNA – transfer RNA[5]

  • Single polynucleotide strand which is folded into three hairpin-loops which gives it a cloverleaf structure, 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.
  • It is typically 76 to 90 nucleotides in length

3. rRNA – ribosomal RNA[6]

  • This is the RNA which forms ribosomes
  • It acts as a catalyst for protein synthesis
  • It is synthesized 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 evolutionary patterns between species since they are all form of life.

The three RNAs all work together to convert the initial DNA molecule into a protein. All three of these types of RNA are synthesized 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 reticulum and X-chromosome inactivation[12]. Besides, 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

  1. ↑ Berg JM, Tymoczko JL and Stryer L, 2007, Biochemistry 6th edition, NY, W. H Freeman and Company, page 109
  2. ↑ Lyons, I, 2011. Biomedical Science Lecture Notes. 1st ed. Oxford: Wiley-Blackwell, p21-23
  3. ↑ Berg JM, Tymoczko JL and Stryer L, 2007, Biochemistry 6th edition, NY, W. H Freeman and Company, page 119
  4. ↑ https://en.wikipedia.org/wiki/Messenger_RNA
  5. ↑ Berg JM, Tymoczko JL and Stryer L, 2007, Biochemistry 6th edition, NY, W. H Freeman and Company, page 120
  6. ↑ Berg JM, Tymoczko JL and Stryer L, 2007, Biochemistry 6th edition, NY, W. H Freeman and Company, page 120
  7. ↑ 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
  8. ↑ 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
  9. ↑ 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
  10. ↑ 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
  11. ↑ 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
  12. ↑ 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
  13. ↑ 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
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