Ribonucleic acid

Power point presentation explains features ,types and functions of RNA (Ribo Nucleic Acid )

1. STRUCTURE OF NUCLEIC ACID : RIBONUCLEIC ACID (RNA ) rRNA,mRNA,tRNA and Micro RNA BY Dr. Ichha Purak University Professor Ranchi Women’s College,Ranchi http://www.dripurak.com/ http://drichhapurak.webnode.com /

2. Friedrich Miescher  in 1869 discovered substance nuclein   from the nuclei of pus cells w hich was later termed nucleic acid because of having phosphate group and was of acidic nature. Nucleic acids are present in all living organisms ( plants,animal,bacteria and even Virus and viriods ) and therefore origin of life is suspected with the formation of nucleic acids. All living cells contain both DNA and RNA, while viruses contain either DNA or RNA, usually not both. 3/12/2013 Structure of Nucleic Acid:RNA 2

3. The nucleic acids are most important biological macromolecules responsible for transmission and storage of heredity or genetic information from one generation to next by means of Replication, Transcription and Translation. Nucleic acids are fibre like molecules having much greater length in comparision to diameter Nucleic acids are the found in abundance in all living things, where they function in encoding, transmitting and expressing genetic information The nucleic acids are generally associated with proteins to form nucleoproteins 3/12/2013 Structure of Nucleic Acid:RNA 3

4. There are two types of nucleic acids : RNA (Ribonucleic acid ) = ( Ribonucleotide ) n –A U C G DNA ( Deoxyribonucleic acid )=( Deoxyribonucleotide ) n – A T C G These are polymers consisting of long chains of monomers called nucleotides linked in a chain through phosphodiester bond A nucleotide consists of a nitrogenous base, a pentose sugar and a phosphate group 3/12/2013 Structure of Nucleic Acid:RNA 4

5. There are two related pentose sugars : - RNA contains ribose - DNA contains deoxyribose The sugars have their carbon atoms numbered with primes to distinguish them from the nitrogen bases 3/12/2013 5 Structure of Nucleic Acid:RNA

6. Nitrogen Bases The nitrogen bases in nucleotides consist of two general types: - pyrimidines : cytosine (C), thymine (T) and Uracil (U) - purines : adenine (A) and guanine (G) 3/12/2013 6 Structure of Nucleic Acid:RNA

7. The primary structure of a nucleic acid is the nucleotide sequence joined by phosphodiester bonds The 3’-OH group of the sugar in one nucleotide forms an ester bond to the phosphate group on the 5’-carbon of the sugar of the next nucleotide 3/12/2013 7 Structure of Nucleic Acid:RNA

8. Reading Primary Structure A nucleic acid polymer has a free 5’-phosphate group at one end and a free 3’-OH group at the other end The sequence is read from the free 5’-end using the letters of the bases This example reads 5’ — A — C — G — T — 3 ’ 3/12/2013 8 Structure of Nucleic Acid:RNA

9. Example of RNA Primary Structure In RNA, A, C, G, and U are linked by 3’-5’ ester bonds between ribose and phosphate 3/12/2013 9 Structure of Nucleic Acid:RNA

10. RNA is polymer of Ribonucleotides RNA is a polymeric constituent of all living cells and many viruses. it is long single stranded chain of alternating phosphate and ribose sugar units with the nitrogenous bases Adenine & guanine ( purines ) and cytosine and uracil ( pyrimidines ) bonded to ribose sugar . RIBONUCLEIC ACID (RNA ) 3/12/2013 Structure of Nucleic Acid:RNA 10

11. Chemical structure of RNA 3/12/2013 Structure of Nucleic Acid:RNA 11

12. RBONUCLEOTIDES (AMP )adenosine monophosphate ( GMP) gwanosine monophosphate PURINES (CMP) cytidine monophosphate (UMP) uridine monophosphate PYRIMIDINES

13. 13 Structure Of RIBO Nuclic Acids Polymers of four nucleotides Linked by alternating sugar-phosphate bonds RNA: ribose and A, C, G, U P sugar A P sugar G P sugar C P sugar U AMP CMP GMP UMP

14. RNAs are usually single stranded, but many RNA molecules have secondary structure in which intramolecular loops are formed by complementary base pairing ( tRNA and rRNA ). Base pairing in RNA follows exactly the same principles as with DNA: the two regions involved in duplex formation are antiparallel to one another, and the base pairs that form are A-U and C-G 3/12/2013 Structure of Nucleic Acid:RNA 14

15. RNA is much more abundant than DNA DFFERENCES BETWEEN RNA AND DNA S N RNA DNA 1 RNA is polymer of Ribonucleotides DNA is polymer of Deoxyribonucleotides 2 RNA has Ribose sugar DNA has Deoxyribose sugar 3 Ribose sugar (C5H10O5) has OH- at C2,C3 &C5 Deoxyribose Sugar has OH- only at C3 & C5 4 RNA is generally single stranded Exception tRNA & rRNA at some places are double stranded DNA is Generally Double Stranded Exception In Bacteriophage Ф- 174 and S-13 5 RNA has Pyrimidines Cytosine and Uracil DNA has Pyrimidines Cytosine and Thymine 6 RNA generally Non Genetic but in some Viruses it is Genetic Material DNA is Genetic Material 3/12/2013 Structure of Nucleic Acid:RNA 15

16. 7 RNA is not stable DNA is stable in alkaline condition 8 RNA is synthesized by transcription using one strand of DNA as Template DNA is Synthesized by Replication using both strands of DNA as templates during Interphase 9 In helical regions A-U and C-G are the Base Pairs A- T and C-G are the Base Pairs 10 The helix geometry of RNA is of A-Form Is destroyed by enzymes and produced again The helix geometry of DNA is of B-Form Protects itself against enzymes 11 RNA performs the function of a messenger between DNA and the proteins. DNA performs long term storage and transfer of Genetic Information 3/12/2013 Structure of Nucleic Acid:RNA 16

17. Ribose replaces deoxyribose; uracil replaces thymine RNA 3/12/2013 Structure of Nucleic Acid:RNA 17

18. S N Coding RNA Non-coding RNAs 1 mRNA (Messenger RNA) 2 tRNA ( Transfer RNA) 3 rRNA (Ribosomal RNA 4 snRNA (Small nuclear RNA ) 5 snoRNA (Small nucleolar RNA ) 6 scRNA (Small cytoplasmic RNA) 7 aRNA (Antisense RNA ) 8 miRNA ( microRNA ) 9 si RNA (small interference RNA ) 10 Ribozyme (catalytic RNA ) 11 cRNA (Complementary RNA ) 12 gRNA ( guide RNA ) TYPES OF RNAs 3/12/2013 Structure of Nucleic Acid:RNA 18

19. MAJOR TYPES OF RNAs 3/12/2013 19 Structure of Nucleic Acid:RNA

20. 3/12/2013 20 Structure of Nucleic Acid:RNA SYNTHESIS AND MAIN FUNCTIONS OF DIFFERENT RNAs

21. BRIEF DESCRIPTION OF DIFFERENT RNAs Messenger RNA(mRNA ) - is the only coding RNA as it bears a complementary copy of deoxyribonucleotide sequence present on Gene (DNA segment ) as ribonucleotide sequence. It encodes chemical blueprint for protein synthesis in 5’-3’ direction. It is single stranded 3/12/2013 21 Structure of Nucleic Acid:RNA

22. Transfer RNA ( tRNA ) is a small RNA chain(73-95 nucleotides ) that transfers a specific amino acid to a growing polypeptide chain at ribosome during translation. It acts as a adapter molecule because it can recognise both a specific Amino Acid as well as its codon on mRNA. For loading 20 different protein Amino Acids there are different tRNAs .(1-20) Each amino acid is recognized by one or more specific tRNA tRNA has a tertiary structure that is L-shaped one end attaches to the amino acid and the other binds to the mRNA by a 3-base complimentary sequence Anticodon 3/12/2013 Structure of Nucleic Acid:RNA 22

23. Ribosomal RNA( rRNA ) is the most stable RNA .It is synthesized by Nucleolar genes by RNA polymerase I and make 40-60% by weight of total RNA and is 80% of total RNA of the cell. It may measure upto 7000 A ᵒ in extended form . It is main component of ribosomes along with proteins Ribosomes are the sites of protein synthesis ,consisting of ribosomal RNA (65%) and proteins (35%), have a small and a large subunit 3/12/2013 Structure of Nucleic Acid:RNA 23

24. Small nuclear RNA ( snRNA ) a class of small eukaryotic RNA molecules found in the nucleus usually as ribonucleoproteins which are involved in processing heterogenous nuclear messenger RNA (Splicing of Exons )U1, U2 U4, U5 and U6 and also used in RNA interference 3/12/2013 Structure of Nucleic Acid:RNA 24

25. Small nucleolar RNA ( snoRNAs ) are a class of small RNA molecules that guide chemical modification ( methylation or puedouridylation ) of ribosomal RNAs Small cytoplasmic RNA ( scRNA ) small (7S,129 nucleotides) RNA found in cytosol and rough endoplasmic reticulum associated with proteins ,component of SRP (Signal Recognition Particle ) that are involved in specific selection and transport of secretory proteins by recognizing signal sequence at amino terminus of growing polypeptide chain. 3/12/2013 Structure of Nucleic Acid:RNA 25

26. Signal Sequence directing Protein Targetting 3/12/2013 Structure of Nucleic Acid:RNA 26

27. Antisense RNA ( aRNA ) is a single stranded RNA that is complementary to a mRNA strand . Antisence mRNA (artificially synthesized ) may be introduced into a cell to inhibit translation of a complementary mRNA by base pairing to it and physically obstructing (blocking) the translation machinery. It is thought as promising technique for disease therapy. 3/12/2013 Structure of Nucleic Acid:RNA 27

28. microRNAs ( miRNA ) MicroRNAs were first described in 1993 by Rosalind Lee, Victor Ambros , and Rhonda Feinbaum in the nematode  Caenorhabditis elegans   MicroRNAs constitute a recently discovered class of non-coding RNAs that play key roles in the regulation of gene expression by gene silencing Mature microRNAs are short, single-stranded RNA molecules having about 21- 23 nucleotides in length The genes encoding miRNAs are much longer than the processed mature miRNA molecule MicroRNA genes are transcribed by RNA polymerase II as large primary transcripts ( pri-microRNA ) 3/12/2013 Structure of Nucleic Acid:RNA 28

29. Pri-microRNA has a cap and Poly-A tail before undergoing processing like mRNA Pri-microRNAs are processed by a protein complex Drosha containing RNase III enzyme to form an approximately 70 nucleotide precursor microRNA (pre- microRNA ). This molecule has stem-loop structure This precursor is subsequently transported to the cytoplasm where it is processed by a second RNase III enzyme, DICER, to form a mature microRNA of approximately 22 nucleotides This mature miRNA has some complementary sequences to one or more mRNAs The mature microRNA is then incorporated into a ribonuclear particle to form the RNA-induced silencing complex, RISC, which mediates gene silencing through RNA interference. 3/12/2013 Structure of Nucleic Acid:RNA 29

30. MicroRNAs usually induce gene silencing by binding to target sites found within the 3’UTR of the targeted mRNA. This interaction prevents protein production by suppressing protein synthesis by initiating mRNA degradation Since most target sites on the mRNA have only partial base complementarity with their corresponding microRNA , individual microRNAs may target as many as 100 different mRNAs. MicroRNAs play significant role in cell cycle control,apoptosis,stem cell differentiation etc.MicroRNAs are also involved in tissue-specific expression MicroRNAs are a class of post-transcriptional regulators They are short ~22 nucleotide RNA  sequences that bind to complementary sequences in the 3’ UTR of multiple target mRNAs, usually resulting in their silencing. . 3/12/2013 Structure of Nucleic Acid:RNA 30

31. Processing of miRNA 3/12/2013 Structure of Nucleic Acid:RNA 31

32. Function of Micro RNA ( MiRNA ) Small but mighty   a microRNA (miRNA), silences genes 3/12/2013 Structure of Nucleic Acid:RNA 32

33. Small interfering RNA ( siRNA ) is considered exogenous double-stranded RNA that is taken up by cells, or enters via vectors like viruses, while miRNA is single stranded and comes from endogenous (made inside the cell) non-coding RNA, found within the introns of larger RNA molecules . siRNA are double stranded RNA fragments,which trigger catalytically mediated gene silencing by targetting RNA Induced Silencing Complex ( RISC) to bind and degrade the mRNA Both siRNA and miRNA can play a role in  epigenetics  through a process called  RNA-induced transcriptional silencing (RITS) . Likewise, both are important targets for therapeutic use, because of the roles they play in the controlling gene expression. 3/12/2013 Structure of Nucleic Acid:RNA 33

34. Ribozyme ( Catalytic RNA ) is ribonucleic acid molecules having catalytic activity as protein enzymes Till 1989 it was believed that all enzymes are proteinaceous in nature. During observing spilicing mechanism of Group I rRNA intron from protozoa Tetrahymena thermophila by Thomas Cech and Sydney Altman, it was realized that no proteins were involved in this process. It was revealed that RNAs could also have catalytic function. In this case the rRNA was processed for removal of intron and spilicing exons without any intervention of any protein. This post transcriptional processing of rRNA led to discovery of RNA enzyme or RIbozyme or Non-protein enzymes . Examples RNase P Group I and Group II  introns Peptidyl transferase 23S rRNA 3/12/2013 Structure of Nucleic Acid:RNA 34

35. Splicing mechanism of Group I intron .The nucleophile in the first step may be gwanosine,GMP,GDP or GTP

36. Guide RNA ( gRNA ) are RNA genes that function in RNA editing, found in mitochondria by inserting or deleting stretches of uridylates (Us) . The gRNA forms part of editosome and contain sequences to hybridize to matching sequences in the mRNA to guide the mRNA modifications . Complementary RNA( cRNA ) viral RNA that is transcribed from negative sense RNA and serves as a template for protein synthesis Negative sense RNA viral RNA with a base sequence complementary to that of mRNA during replication it serves as a template to the transcription of viral complementary RNA Positive sense RNA viral RNA with same base sequence as mRNA during replication function as mRNA ,serving as template for protein synthesis 3/12/2013 Structure of Nucleic Acid:RNA 36

37. RNA interference Experimental use by introducing small ds RNAs for functional deactivation of specific genes ,which induces degradation of complementary single stranded mRNA encoded by the gene , gene silencing . RNA interference is a related process in which double stranded RNA fragnments called small interfering RNAs trigger catalytically mediated gene silencing most typically by targeting the RNA induced Silencing Complex (RISC) to bind to and degrade the mRNA Attempts to genetically engineer transgenic plants to express antisense RNA instead activate the RNA pathway, although the processess result in differing magnitude of gene silencing. Well known examples include Flavr Savr tomato and two cultivars of ringspot papaya 3/12/2013 Structure of Nucleic Acid:RNA 37

38. FUNCTIONS OF DIFFERENT RNA mRNA – It carries genetic formation of DNA ( Gene ) for protein synthesis from nucleus to ribosome in the form of genetic code tRNA – Acts as adapter molecule ,carries Amino Acid and drops it to particular location by recognising codon on mRNA by virtue of having anticodon rRNA – It makes complex with proteins and form ribosomal subunits which provide space for protein synthesis ,single ribosomal RNA of smaller subunit helps correct orientation of mRNA during attachment with respect to P and A sites 3/12/2013 Structure of Nucleic Acid:RNA 38

39. 3/12/2013 Structure of Nucleic Acid:RNA 39 snRNA – play significat role in eukayotic mRNA processing By splicing of exons as snRNPs or snurps U1,U2, U4,U5 &U6 scRNA – being component of Signal Recognition Particle (SRP ) helps in targetting of seceretary proteins snoRNA – Plays role in gene silencing miRNA – play important role in gene silencing by blocking mRNA and preventing translation

40. 3/12/2013 Structure of Nucleic Acid:RNA 40 Si RNA – Plays important role in gene silencing by interfering transcription gRNA - help in RNA editing in mitochondria , forms part of editosome and hybridize with matching sequence of mRNA Catalytic RNA – Ribozymes act as protein enzymes in catalyzing removal of intron , peptide bond formation etc aRNA - antisense RNA - is artificially used to block translation of perticular messenger RNAs so as to prevent formation of some harmful proteins

41. 3/12/2013 Structure of Nucleic Acid:RNA 41 THANK YOU