Summary Tut Group Case 2 (RNA) PDF

**Structure RNA** -\>phosphate group -\>sugar (ribose) =\>difference with deoxyribose= 2' C -\>-OH group instead of -H -\>bases (adenine, *uracil,* guanine, cytosine) -\>single stranded -\>anti-parallel structure -\>bases interact with each other (loops) =\> different functions RNA **Differen...

**Structure RNA** -\>phosphate group -\>sugar (ribose) =\>difference with deoxyribose= 2' C -\>-OH group instead of -H -\>bases (adenine, *uracil,* guanine, cytosine) -\>single stranded -\>anti-parallel structure -\>bases interact with each other (loops) =\> different functions RNA **Differences between DNA and RNA** *DNA* *RNA* ------------------------------------------------------------------------ ---------------------------------------------------------------- 2 strands 1 strand Thymine uracil Deoxyribose Ribose Stores genetic information Transfers genetic information Mutations etc have more consequences Mutations have less consequences Mutations/mistakes happen less often, good proofreading, more accurate More mutations, mistakes, less stable, more prone to reactions Longer strands Shorter strands **differences/similarities transcription and replication** *Similarities* *differences* ----------------------------------------------- ---------------------------------------------------- Transcribed/replicated in 5'-3' RNA polymerase-DNA polymerase Many proteins involved Post-transcriptional modifications (splicing etc.) 3 steps-\>initiation, elongation, termination Transcription=\>1 strand copied Transcription bubble Transcription=\>only specific part DNA copied Start and stop at specific places dNT-\>replication/NT-\>translation **Functions RNA** 1. [Primary functions ] - Facilitate translation of DNA into proteins - Adapter molecule in protein synthesis - Messenger between DNA and ribosomes - Carrier genetic information - Primary genetic material for viruses - RNA editing - Gene regulation - RNA interference 2. [Specific functions ] - mRNA (messenger) : decoding amino acids sequence of polypeptide\> produces + translation of polypeptide. Contains genetic blue print to synthesize proteins. [rapidly degraded by nucleases-\>NOT stable] - tRNA (transfer) : transport of amino acids to ribosomes. Translation of mRNA into protein, [stable molecules] - snRNA (small nuclear) : +proteins= forms complex that is used in eukaryotic RNA processing to produce functional mRNA. =\>splicing - rRNA (ribosomal) : makes up much of the ribosome, [stable molecules], most abundant type of RNA. Consist of 2 pieces and proteins (different for eukaryotes and prokaryotes) **DNA transcription** =synthesizing 1 strand RNA = copy of 1 strand DNA =transferring genetic information in DNA base sequences into RNA base sequences -\>template strand = 3'-5' (DNA) -\>RNA polymerase synthesizes in 5'-3' -\>RNA polymerase catalyzes the transcription process -\>3 stages of transcription -\>transcription bubble = temporary and small -\> template strand DNA = non-coding strand (+ strand) -\> non-template strand DNA (- strand) =coding strand-\>same code as the mRNA strand (T=\>U) -\>prokaryotes: transcription + translation-\> same time in cytoplasm -\>eukaryotes: transcription + translation-\>different places in the cell *1) initiation* -basal transcription factors bind to promotors (help RNA polymerase to bind to promotor region DNA ) \- topoisomerase unwinds the DNA strand and brings it back in original state -\> in front of bubble = positive supercoiling -\>behind bubble = negative supercoiling -\>short RNA primer is synthesized 2\) elongation -\>adding ribonucleotide bases (A+U, C+G) -\>5'-3' direction -\>complementary to template strand DNA (3'-5') 3\) termination -\>RNA synthesis stops at the CG rich sites in DNA (pause-sites) (prokaryotes) *-\>Modifications -\> pre-RNA to mature RNA* *[Eukaryotes ]* =\>NO SPECIFIC 'STOP' SIGNAL, only protection -**5' cap** +GTP (guanine triphosphate) -\>protection 5' against degradation -\>added in the opposite position =\> result is strand with 2x 3'-side (**protection against 5' nucleases**) Other purposes 5' cap - recognition mRNA by ribosomes - transport out of nucleus - regulation start of translation **-poly A tail** =\>CPSF, CSTF (proteins)-\> both bind to a specific sequence -\>proteins bind to each other =\> form a loop=\>enzymes introduce a breakage in the loop -\>poly A tail gets added to the breakage in mRNA (50-250 A bases)=\> enzyme polyA polymerase =\>stabilized by polyA binding proteins Function polyA tail - increased stability by protection against ribonucleases (exonuclease activity) - helps in translation **-5' cap binds to polyA tail with proteins** -\>additional protection -\>important for start translation *Why protection against exonuclease activity=\> exonuclease happens faster than transcription=\>when exonuclease and RNA polymerase meet=\>RNA polymerase gets detached from the DNA strand. 3'prime exonuclease activity ?* **-removal introns=\>splicing** Intron=non-translated region -\>cut-out the introns, glue the exons= mature mRNA How?=\> pre-mRNA has 3'-splice junction and 5'-splice junction -\>snRNPs (snurps=small nuclear ribonucleoproteins) =\>bind to splice-junctions , also to branch point on 5' (branch is part of the intron) -\>additional snurps bind to 3' splice junction and 5' branch point =\>combine and form a loop =\> forms a [spliceosome] =\> intron is cut from the exons (loop is called a lariot) and exons can bind back together -\>lariot ( remaining RNA ) =degraded and reused *Alternative splicing* = all introns are removed, exons CAN be removed - other sequences, different mRNA from 1 strand DNA , different type of proteins *[MATURE mRNA -\>leaves nucleus ]* *[Prokaryotes ]* -*RHO-dependent factor* -\> specific RHO enzyme =\>recognizes sequence in RNA =\>binds =\>causes dissociation of holoenzyme -*RHO-independent factor* -\>formation of hairpin loops =\>RNA polymerase falls of the DNA strand (destabilization DNA-RNA hybrid) **6 different levels where regulation of protein production can take place**