RNA-Ribonucleic Acid PPT
- 1. RIBO NUCLEIC ACIDS PRESENTED BY, KARAN N M.S.c BIOTECHNOLOGY JSSAHER
- 2. RNA - INTRODUCTION . • Ribonucleic acid (RNA) is a polymeric moleculeessential in various biological roles in coding, decoding,regulation and expression of genes. • Like DNA, RNA is assembledas a chain of nucleotides,but unlike DNA, RNA is found in nature as a single strand foldedonto itself,rather than a paired doublestrand. • RNA moleculesplay an active role within cellsby catalysing biological reactions, controlling gene expression,or sensing and communicating responsesto cellular signals. • One of these active processesis protein synthesis, a universal function in which RNA molecules direct the synthesis of proteins on ribosomes. • In 1961French scientists Francois jacob and Jacques monod hypothesizedthe existence of an intermediary between DNA and its protein products. • The structure of the RNA moleculewas first described by R.W. Holley in 1965.
- 3. RNA - STRUCTURE . • RNA is typically single stranded and is made of ribonucleotidesthat are linked by phosphodiesterbonds. • The strand has a 5´end with a phosphate group and 3’ end with hydroxyl group. • A ribonucleotidein the RNA chain contains ribose( the pentose sugar),with carbons numbered 1 to 5. one of the four nitrogenous bases(A,U, G, and C) that is attached to 1st position and a phosphate group that is attached to 3rd position of one ribose and 5th position of the next. • The phosphate groupshave negative charge making RNA negative charged molecule. • The bases form hydrogen bonds between cytosine and guanine, between adenine and uracil and between guanine and uracil. • An important structural component of RNA that distinguishes it from DNA is the presence of a hydroxyl group at the 2nd position of the ribose sugar.
- 5. RNA – II STRUCTURE . FLEXIBILITY INCREASES STABILITY!!!
- 6. RNA - TYPES . In both prokaryotes and eukaryotes,there are three main types of RNA- 5% 80% 15% rRNA tRNA mRNA
- 7. Messenger RNA . • MessengerRNA comprises only 5% of the RNA in the cell. • It is the most heterogenoustype of RNA in terms of size and base sequence. • All members of this class function as messengerscarrying the information in a gene to the protein synthesizing machinery. • the mRNA moleculesare formed with the help of DNA template during the process of transcription. • The sequence of nucleotides in mRNA is read in the form of codons. • A codon is made up of 3 nucleotides. • The mRNA is formedafter processing of heterogenous nuclear RNA. • The 5’ terminal end is capped by 7 methyl guanosine triphosphate cap. • The cap is involvedin the recognition of mRNA by the translating machinery. • It stabilizesmRNA by protecting it 5’ exonuclease activity.
- 8. mRNA-STRUCTURE . • The 3’ end of most mRNAs have a polymerof adenylate residues. • This tail prevents the attack by 3’ exonucleases. • On both 5’ and 3’ end there are non coding sequences which are not translated(NCS). • The intervening region between non coding sequences present between 5’ and 3’ is called coding region. This region encodes for the synthesis of a protein.
- 10. TRANSFER RNA . • Transfer RNA are the smallest of the three major species of RNA molecules. • On average they have 74-95nucleotide residues. • They are synthesized by the nuclear processingof a precursor molecule. • They transfer the amino acids from cytoplasm to the protein synthesizing machinery, hence the name tRNA. • They are also called adapter molecules,since they act as adapters for the translation of the sequence of nucleotidesof the mRNA in to specific amino acids. • There are at least 20 species of tRNA one corresponding to each of the 20 amino acids required for protein synthesis. • They are easily soluble,hence they are also known as solubleRNA or sRNA.
- 11. TRANSFER RNA . • Primary structure- the nucleotide sequence of all the tRNA moleculesallows for the extensive intrastand complementarity that generates a secondary structure. • Secondary structure- Each single tRNA shows extensive internal base pairing and acquires a clover leaf like structure. The structure is stabilized by hydrogen bonding between the bases and is a consistent feature.
- 12. TRANSFER RNA . All tRNA contain 5 main arms or loops.Which are as follows: • Acceptor arm 1. The acceptor arm is at 3’ end and It has 7 base pairs. 2. The 3’ OH group terminal of adenine binds with carboxyl group of amino acids, the tRNA bound to amino acid is called amino acyl tRNA. • Anticodon arm 1. Lies at the oppositeend of acceptor arm and it is 5 base pairs long. 2. It binds to codons in mRNA during translation. • DHU arm - Serves as recognition site for amino acyl tRNA synthase that adds amino acid to the acceptor arm. • T arm- it is involved in binding of tRNA to the ribosomes • Extra arm or variable arm- about 75% of tRNA moleculepossessa short variable arm.
- 13. RIBOSOMAL RNA . • rRNAs are found in the ribosomesand account for 80% of the total RNA present in the cell. • Ribosomesare composedof a large subunit called the 50S and a small subunit called the 30S in prokaryotesand 60S and 40S in eukaryoteseach of which is made up of its own specific rRNA molecules. • Different rRNAs present in the ribosomesinclude small rRNAs and large rRNAs, which belong to the small and large subunits of the ribosome,respectively. • rRNAs combine with proteins and enzymes in the cytoplasm to form ribosomes,which act as the site of protein synthesis. These complex structures travel along the mRNA moleculeduring translation and facilitate the assemblyof amino acids to form a polypeptidechain. • They interact with tRNAs and other moleculesthat are crucial to protein synthesis. • In bacteria, the small and large rRNAs contain about 1500 and 3000 nucleotides,respectively, whereas in humans, they have about 1800 and 5000 nucleotides,respectively.However, the structure and function of ribosomesis largely similar across all species.
- 14. RIBOSOMAL RNA . S stands for svedberg constant.
- 15. OTHER TYPES OF RNA . Small nuclear RNA (snRNA) siRNA micro RNA (miRNA) Ribozymes (RNA enzymes) Double-stranded RNA (dsRNA) snRNA is involved in the processing of pre- messenger RNA (pre- mRNA) into mature mRNA. They are very short, with an average length of only 150 nucleotides. siRNA (20-25 nt) are often produced by breakdown of viral RNA, though there are also endogenous sources of siRNAs. An mRNA may contain regulatory elements itself, such as riboswitches, in the 5' untranslated region or 3' untranslated region; these cis-regulatory elements regulate the activity of that mRNA. miRNA (21-22 nt) is found in eukaryotes, and acts through RNA interference (RNAi). miRNA can break down mRNA that it is complementary to, with the aid of enzymes. This can block the mRNA from being translated, or accelerate its degradation. RNAs are now known to adopt complex tertiary structures and act as biological catalysts. Such RNA enzymes are known as ribozymes. One of the first ribozymes to be discovered was RNase P, a ribonuclease that is involved in generating tRNA molecules from larger, precursor RNAs. This type of RNA has two strands bound together, as with double-stranded DNA. dsRNA forms the genetic material of some viruses..
- 16. REFERENCES
- 17. THANK YOU