REGULASI EKSPRESI GENAndriani Dept. Biokimia dan Biologi Molekuler FK UNTAN EKSPRESI GEN - Dari keseluruhan genom, ekspresi sebuah gen berlangsung pada suatu waktu saat diperlukan - Keseimbangan jumlah protein dalam sel diatur oleh mekanisme : 1. Transkripsi 2. Posttranscriptional modification of mRNA 3. Messenger RNA degradation 4. Protein synthesis (translation) 5. Posttranslational modification of proteins 6. Protein targeting and transport 7. Protein degradation EKSPRESI GEN • Housekeeping gene : jumlah konstan dalam sel • Regulated gene expression : jumlah bisa meningkat dan menurun tergantung sinyal INDUKSI (Positive Regulation)→ proses peningkatan ekspresi REPRESI (Negative Regulation) → penurunan ekspresi Dobel negative ~ INDUKSI DOGMA SENTRAL DNA RNA Protein REGULASI GEN PADA PROKARIOTA • Model mempelajari regulasi ekspresi pada E. Coli • Bakteri mensintesis enzim berdasarkan nutrisi pada lingkungannya • Selain glukosa dan laktosa, juga memerlukan aa triptofan • Ketika E. Coli berada pada medium triptofan, akan diabsorbsi • Jika triptofan (-) , sintesis • OPERON : - Situs promotor : tempat melekatnya RNA polymerase dan awal transkripsi - Daerah terbentuknya repressor • Operator berada pada DNA diantara promotor dan gen struktural yang akan di transkripsi OPERON TRIPTOFAN • Aa triptofan dikode 5 gen struktural • RNA polimerase terikat pada promotor (pada permulaan gen pertama) • Mekanisme on-off OPERON LAC • Selain aa, E. Coli mencerna gula laktosa pada lingkungan (jacques Monod dan Francois Jacob) • E. Coli mengekspresikan beta galaktosidase untuk mencerna laktosa Lac Z gene • Pengaturan ekspresi Beta galaktosidase dilakukan oleh protein regulator : repressor • Represor terikat pada gen Lac Z pada daerah antara promotor dan start kodon gen struktural : operator • • Dalam keadaan normal (tanpa laktosa) repressor menduduki operator : OFF • Dalam keadaan laktosa (+), repressor mengikat laktosa, : ON REGULASI EKSPRESI GEN PADA EUKARIOTA prokaryotes Respond Short term Immediate environtment (external) Survival of individual cell Regulate Long term Homeostasis(internal) Needs of whole organism Eukaryotes Regulation in eukaryote can be regulated at four distinct levels. INTRONS AND EXONS • Eukaryotic DNA differs from prokaryotic DNA it that the coding sequences along the gene are interspersed with noncoding sequences • The coding sequences are called – EXONS • The non coding sequences are called – INTRONS INTRONS AND EXONS • After the initial transcript is produced the introns are spliced out to form the completed message ready for translation • Introns can be very large and numerous, so some genes are much bigger than the final processed mRNA INTRONS AND EXONS • Muscular dystrophy • DMD gene is about 2.5 million base pairs long • Has more than 70 introns • The final mRNA is only about 17,000 base pairs long RNA Splicing • Provides a point where the expression of a gene can be controlled • Exons can be spliced together in different ways • This allows a variety of different polypeptides to be assembled from the same gene • Alternate splicing is common in insects and vertebrates, where 2 or 3 different proteins are produced from one gene MODIFIKASI KROMATIN - Modifikasi melalui aa yang terdapat pada protein histon - Metilasi DNA : pada GC Rich sequence ASETILASI PROTEIN HISTON Cis-acting element cis-acting element structural gene GCGC CAAT TATA exon intron exon start TATA box (Hogness box) enhancer GC box CAAT box DNA BENDING PROTEIN • • • • Zinc fingers B- zip protein Helix turn helix Helix loop helix MODIFIKASI POST TRANSKRIPSI