Biochem - Rna

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Mrna

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Messenger RNA’s, code for proteins (5%)

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RRNA

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Ribosomal RNA’s, basic structure of the ribozome, catalyze protein synthesis 80%

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trna

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Transfer RNA’s, read the genetic code on mRNA’s delivering the amino acids in protein synthesis (15%)

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SNRNA

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Small nuclear RNA’s, involved in pre m-RNA splicing

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SNORNA

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Small nucleolar RNA’s, process and chemically modify rRNA’s

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MIRNA/sinrna

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MicroRNA, Small Interfering RNA, 22nt’s, regulate the expression of mrna

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Other non-coding rna

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Telomere synthesis, X-chromosome inactivation, protein transport,…

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main differences between RNA and DNA

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the ribose on RNA lacks a hydroxyl group. RNA also uses uracil instead of thymine. RNA can form complex structures. Additionally during RNA synthesis only one strand is copied but multiple copies can be made. Only select areas are copied.

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rna pol I

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final product of rRNA

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rna pol II

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m RNA and sn RNA as its final products

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rna pol III

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trna

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requirements for RNA synthesis

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double-stranded DNA template, all four ribonucleotide triphosphate's, magnesium and zinc, but does not require a primer unlike DNA synthesis

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describe proofreading capacity of RNA

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It has 3 to 5 exonuclease activity and proofreading capacity but is 1000 times less accurate than DNA polymerase.

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synthesis, processing and localization of rRNA

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rRNA's are generated from long precursor molecules called pre – rRNA's. These are cleaved by ribonucleases which are further processed to produce the required RNA species. RRNA genes are found in long tandem arrays and synthesis occurs in the nucleolus. Base and sugar modifications are facilitated by small nuclear RNAs or snoRNA

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two functions played by rRNA in protein synthesis

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it plays a structural role as a component of the ribosomes the physical locus of protein synthesis in addition it is recently been confirmed that rRNA is a ribozyme and is capable of self splicing. It catalyzes the formation of the peptide bond between amino acids

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function of snoRNA

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primarily guide chemical modifications of other RNAs, mainly ribosomal RNAs, transfer RNAs and small nuclear RNAs.

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ribozyme

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RNA folded similar to protein with a catalytic function.

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how mRNA is produced as hnRNA and modified with the use of snRNA and proteins to form mRNA

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When pre-mRNA comes off the transcription machinery its code proteins and RNA molecules that define the exon intron boundaries. The long intron are then packaged into hnRNP. The term hnRNA is given to the nascent transcript arising from synthesis by RNA polymerase 2.

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cloverleaf

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secondary structure of tRNA. It has an anti-codon arm and on the other side and amino acid attached The anti-codon arm binds to the codon in mRNA in a ribosome and extends the polypeptide chain.

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leg of lamb

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tertiary structure tRNA.

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overview of the steps in transcription of a DNA segment to form mature mRNA

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eukaryotes require basal or general transcription factors. These bind to a TA TA box which is easier to unwrap then GC base pairs. TF two binds to the TA TA box and recruits RNA polymerase II this is the pre-initiation complex. The steps in transcription include formation of the pre-initiation complex. Unwinding of the DNA double helix with the helicase enzyme. Synthesis of RNA based on the sequence of the DNA template strand, termination of synthesis at a transcription stop signal followed by post-transcriptional processing

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importance of 5’ capping

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The addition of the five prime cap consists of a seven methyl guanosine. The addition of the Helps to stabilize the mRNA and permits initiation of translation. Eukaryotic mRNAs lacking this Are not officially translated cap are not efficiently translated.

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importance of 3' polyadenylation

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Most eukaryotic mRNA has an additional chain of 40 to 200 adenine nucleotides attached to the three prime end. This helps to stabilize the mRNA, facilitate its exit from the nucleus, and aid in translation.

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enzymes involved in 5’ capping

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quanyltransferase which adds GMP. Methylation is catalyzed by quanyl – 7 – methyltransferase.

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enzymes involved in 3'polyadenylation

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polyadenylate polymerase.

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mechanism of RNA splicing?

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The molecular complex that account versus splicing is known as the spliceosome. Uracil rich small nuclear RNAs or snRNA form small nuclear ribonucleoprotein particles or SNRNP’s they facilitate the removal of entrance by forming base pairs with the consensus sequence at the end of each intron. The binding of snRNP’s razor to prime hydroxyl end of the branch site to the five prime end of the splice donor site forming a 2-5 phosphodiester bond and a lariat. This is then released and the two exons are formed.

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Why is the specificity of the splicing reaction important?

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The specificity of the splicing reaction is important because the splicing happens in the wrong place either the RNA will code for a nonfunctional protein or the wrong protein.

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explain alternative splicing and tailing

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alternative splicing and alternative tailing changes the functional versatility of the genes. Therefore the same gene can code for multiple proteins based on differential splicing and tailing of the particular mRNA.

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what does the death cap mushroom inhibit

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RNA pol II

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preinitation complex

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TF II binds to TATA box which recruits RNA pol II