6/5/201811BY311/511 Molecular GeneticsLecture 2Eukaryotic Gene Structure and its Upstream Regulatory GeneticElementsLewin’s XII – Chapter 18Prokaryotic transcription and translation occur simultaneously in the cytoplasm,and regulation occurs at the transcriptional level. Eukaryotic gene expression isregulated during transcription and RNA processing, which take place in thenucleus, and during protein translation, which takes place in the cytoplasm.Further regulation may occur through post-translational modifications of proteins.Difference between prokaryotic and eukaryotic gene regulationSource: Boundless. “Prokaryotic versus Eukaryotic Gene Expression.”Boundless Biology.-versus-eukaryotic-gene-expression-453-11678/Bacteria: Transcription and Translation – Coupled –Events occur in a single compartmentEukaryotic: Transcription and Translation –Truncated – Events occur in different compartments().5’-AUGACG GAUCAGC CGCA AGCG GA AU UGGC– 3’OH3’5’3’5’GenomeChromatinHistone+ DNADNAGene StructureTranscription of a geneCoding DNA Strand/Non-template DNAStrandNon-codingDNAstrand/Template DNA StrandRNAPolymerasemRNADirection of TranscriptionGenome, Genes, DNA, Transcription – An overviewLewin’s Genes XII - 2018.34Eukaryotic gene structure: General Considerations1. Unlike prokaryotes, eukaryotic cells possess anucleusand a nuclear membrane.2. The chromosome is located in the nucleus thereforethetranscription occurs in the nucleus.3. Transcription is conducted bya DNA-dependent RNApolymerase IIonprotein-coding genesresulting intoan mRNA.RNA pol I = rRNARNA pol II = mRNARNA pol III = tRNA; 5S rRNA
6/5/2018218.2Eukaryotic RNA PolymerasesConsist of Many Subunits4.RNA polymerase I synthesizes rRNA in the nucleolus.5.RNA polymerase II synthesizes mRNA in thenucleoplasm.6.heterogeneous nuclear RNA (hnRNA) –RNA thatcomprises transcripts of nuclear genes made primarily byRNA polymerase II; it has a wide size distribution andvariable stability.7.RNA polymerase III synthesizes small RNAs (tRNA; 5SrRNA) in the nucleoplasm.Lewin’s Genes XII - 20186Eukaryotic gene structure: General Considerations8.The mRNA when just synthesized is unprocessed,consists of alternating introns and exons and referredas“heterogeneous nuclear RNA” or hnRNA.9.ThehnRNA is processed by the RNA polymerase IIenzyme and other proteinsin3 consecutive stepsduring synthesis:(i)5’-CAP structure(ii) splicing of introns, and(iii) 3’-poly(A) tail, respectively.