14- DM Oral Biochemistry-SPBU- Lecture 14.pdf

1 Gene Expression The multistep process Functional gene product protein RNA 2 Levels of Gene Expression Level1 Level 2  Constitutive Vs Regulated Genes Constitutive...

1 Gene Expression The multistep process Functional gene product protein RNA 2 Levels of Gene Expression Level1 Level 2  Constitutive Vs Regulated Genes Constitutive Regulated genes (housekeeping genes) They are continually expressed They are expressed only under (not regulated) certain conditions Regulation of gene expression in prokaryotes In prokaryotes genes organized in a group called operons Promotor Operons Structural genes code operator for proteins needed  is a DNA segment that allows promotor a gene to be transcribed. is a part of DNA that turns a operator gene “on” or ”off.” Regulation of gene expression in Eukaryotes I- Pre-transcriptional Regulation of gene II- Transcriptional expression Regulation of gene expression (Epigenetic mechanisms) III- Post-transcriptional Regulation of gene expression II- Transcriptional Regulation of gene expression 8 II-Transcriptional regulation of gene expression Regulatory Regulatory proteins are sequences on called DNA are called trans-acting cis-acting elements elements e.g. (Transcription (Enhancers & factors) Silencers)  DNA Enhancer Special DNA sequences that increase the rate of initiation of transcription of a specific gene Enhancer TATA CAAT Core promoter 10 III- Post-transcriptional Regulation of gene expression  Posttranscriptional Modifications in eukaryotes All three types of RNAs are synthesized in precursor forms in eukaryotes. These precursors are converted to functional mature RNA molecules by post-transcriptional modifications. In Eukaryotes messenger RNA Post-transcriptional modifications 1-Capping at 5’end 2- Splicing (Removal of introns & splicing of exons) 3-Addition of poly (A) tail at 3’ end. Newly synthesized mRNA combines with a protein to form mRNA-protein complex, which comes out through nuclear pore.  1-Capping at 5′ end Methyl-guanosine cap is added at the 5' end  2. Addition of a poly-A tail Poly (A) polymerase (PAP) is responsible for the addition of poly(A) tail at the 3`end of pre-mRNA.  3- Splicing (Removal of introns & splicing of exons) Introns Exons Parts of hnRNA do not contain Parts of hnRNA any genetic which carry information. genetic These unwanted information that or intervening will be translated sequences into protein Primary mRNA Exons Introns Exons Introns Exons Introns Exons Introns Exons Exons Exons Exons Protooncogenes and oncogenes protooncogene Oncogene Gene whose protein product Altered normally play role protooncogene in regulating normal cell cycle Involved in signal Protein capable of transduction and producing cancer Normal cell growth Protooncogenes and oncogenes Mutation Over expression Protooncogene Genetic damage Oncogene Difference is related to activity or amount of protein product of the gene  Activity 1 (Match) Column A Column B 1- In prokaryotes genes organized in a group A- Protooncogenes. called. 2- Genes are expressed only under certain B- Exons. conditions. 3- A part of DNA that turns a gene “on” or ”off.” C- Enhancers 4- Genes whose protein product normally play D- Operator. role in regulating normal cell cycle. 5- Parts of hnRNA which carry genetic E- Regulated genes. information that will be translated into protein. 6- Special DNA sequences that increase the rate F- Operons. of initiation of transcription of a specific gene. Extended Modular Program