RNA

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RNA stands for ribonucleic acid. RNA is made up of ribose, a five carbon sugar, and phosphate which forms the backbone. Attached to this backbone are 4 bases, in a similar way to DNA where cytosine (C) pairs with guanine (G) and thymine (T) pairs with adenine (A), in RNA C pairs with G, but A pairs with 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>
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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.  
  
== <br>RNA involved in gene expression ==
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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.
  
1. mRNA – messenger RNA <ref>Berg JM, Tymoczko JL and Stryer L, 2007, Biochemistry 6th edition, NY, W. H Freeman and Company, page 119</ref><br>
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== RNA involved in gene expression  ==
  
&nbsp;&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; - DNA is transcribed into mRNA, therefore the mRNA and the DNA are complementary<br>&nbsp;&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; - This mRNA is then used as a template for translation into a functioning protein<br>&nbsp;&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; - mRNA is also used to make copy DNA (cDNA)<br>2. tRNA – transfer RNA<ref>Berg JM, Tymoczko JL and Stryer L, 2007, Biochemistry 6th edition, NY, W. H Freeman and Company, page 120</ref><br>&nbsp;&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; - consists of a sequence of three bases and an associated amino acid<br>&nbsp;&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; - This molecule travels to the ribosome where a polypeptide is formed, the sequence of which was determined by the mRNA.<br>3. rRNA ribosomal RNA&nbsp;<ref>Berg JM, Tymoczko JL and Stryer L, 2007, Biochemistry 6th edition, NY, W. H Freeman and Company, page 120</ref><br>&nbsp;&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; - This is the RNA found in ribosomes<br>&nbsp;&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; - It acts as a catalyst for protein synthesis
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=== 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> ===
  
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*Single polynucleotide strand made in the nucleus during [[Transcription|transcription]]
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*DNA is transcribed into mRNA by an RNA polymerase, therefore the mRNA and the DNA are complementary
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*mRNA carries the [[Genetic code|genetic code]] from the DNA in the nucleus to the [[Ribosomes|ribosomes]] in the [[Cytoplasm|cytoplasm]]
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*This mRNA is then used as a template for [[Translation|translation]] into a functional protein
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*mRNA is also used to make copy DNA([[CDNA|cDNA]])
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*The short-lived, unprocessed or partially processed product is termed precursor mRNA or pre-mRNA; once completely processed, it is termed mature mRNA
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*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>
  
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=== 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>  ===
  
== References ==
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*Single polynucleotide strand which is folded into three hairpin-loops which gives it a cloverleaf structure, held together by [[Hydrogen bonds|hydrogen bonds]]
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*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
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*Found in the [[Cytoplasm|cytoplasm]], where it is involved in translation
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*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]].
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*It is typically 76 to 90 nucleotides in length
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=== 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>  ===
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*This is the RNA which forms [[Ribosomes|ribosomes]]
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*It acts as a catalyst for [[Proteins|protein]] synthesis
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*It is synthesized in the [[Nucleolus|nucleolus]]
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*rRNA molecules do not code for protein
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*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.
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*It is used to work out evolutionary patterns between species since they are all form of life.
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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.
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=== 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>  ===
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*commonly known as U-RNA
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*function in various nuclear processes
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*function in the splicing of pre-mRNA
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*transcribed by either RNA polymerase II or RNA polymerase III
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=== 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>  ===
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*used to process and modify rRNA chemically
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=== 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>  ===
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*a class of snoRNAs
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*locate at the Cajal body
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*to modify snoRNA and snRNA
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=== 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>  ===
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*non-coding RNA molecule
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*containing approximately 22 nucleotides
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*regulate gene expression by blocking translation of selective mRNA
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=== 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>  ===
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*also known as silencing RNA
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*double-stranded RNA molecules
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*turn off gene expression by directing degradation of selective mRNA and the establishment of compact chromatin structures
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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>.
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== 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.

Contents

RNA involved in gene expression

1. mRNA – messenger RNA[3]

2. tRNA – transfer RNA[5]

3. rRNA – ribosomal RNA[6]

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]

5. snoRNA - small nucleolar RNA[8]

6. scaRNA - small cajal RNA[9]

7. miRNA - microRNA[10]

8. siRNA - small interfering RNA[11]

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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