Survey
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Download Gene Regulation results in differential Gene Expression, leading to
Transcript
GENE REGULATION RESULTS IN DIFFERENTIAL GENE EXPRESSION, LEADING TO CELL SPECIALIZATION Eukaryotic DNA Epigenetics – Ghost in Your Genes Watch to see how your environment and your choices influence inheritance… http://www.youtube.com/watch?v=CiAyLPeCTMU& feature=share&list=PLA2E1F3FFBFAE1CB6 Differential Gene Expression Nucleosome Packing: DNA wraps around histone proteins to form a structure called a nucleosome. Nucleosomes help pack DNA into eukaryotic chromosomes. When acetyl groups attach to the histone proteins the DNA in chromosomes loosens to allow for transcription. The addition of methyl groups to histone proteins can cause DNA to condense thus preventing transcription. In Genomic Imprinting, methylation regulates expression of either the maternal or paternal alleles of certain genes at the start of development. Fig. 18-8-3 Organization of Typical Eukaryotic Genes Enhancer (distal control elements) Poly-A signal sequence Proximal control elements Termination region Exon Intron Exon Intron Exon DNA Upstream Promoter Primary RNA 5 transcript Downstream Transcription Exon Intron Exon Intron Exon RNA processing Cleaved 3 end of primary transcript Poly-A signal Intron RNA Coding segment mRNA 3 5 Cap 5 UTR Start codon Stop codon 3 UTR Poly-A tail The Roles of Transcription Factors Regulatory Proteins, repressors and activators, operate similarly to those in prokaryotes, influencing how readily RNA polymerase will attach to a promoter region. In many cases, numerous activators are acting in concert to influence transcription. Fig. 18-9-3 Promoter Activators DNA Enhancer Distal control element Gene TATA box General transcription factors DNA-bending protein Group of mediator proteins RNA polymerase II RNA polymerase II Transcription initiation complex RNA synthesis Coordinately controlled eukaryotic genes A particular combination of control elements can activate transcription only when the appropriate activator proteins are present. All cells of an organism have all chromosomes/genes but certain genes are only active in certain cells. The transcription factors present in the cell determine which genes will be active and which won’t (but they are both still present) Fig. 18-10 Enhancer Control elements Promoter Albumin gene Crystallin gene LIVER CELL NUCLEUS LENS CELL NUCLEUS Available activators Available activators Albumin gene not expressed Albumin gene expressed Crystallin gene not expressed (a) Liver cell Crystallin gene expressed (b) Lens cell Post Transcriptional Regulation Alternate Gene Splicing - different mRNA molecules are produced from the same primary transcript, depending on which RNA segments are treated as exons and which as introns Fig. 18-11 Exons DNA Troponin T gene Primary RNA transcript RNA splicing mRNA or Noncoding RNAs role in gene expression RNA Interference, noncoding RNAs play multiple roles in controlling gene expression. MicroRNAs (miRNAs) and Small inserting RNAs (siRNAs) are small single-stranded RNA molecules that can bind to mRNA. These can degrade mRNA or block its translation. The difference between the two is that they form from different RNA precursors. Fig. 18-13 Hairpin miRNA Hydrogen bond Dicer miRNA 5 3 (a) Primary miRNA transcript mRNA degraded miRNAprotein complex Translation blocked (b) Generation and function of miRNAs
