* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Download Lecture#7 - Eukaryote gene structure and regulation.
Pathogenomics wikipedia , lookup
Cancer epigenetics wikipedia , lookup
RNA interference wikipedia , lookup
Metagenomics wikipedia , lookup
Transposable element wikipedia , lookup
Epigenetics of diabetes Type 2 wikipedia , lookup
Gene desert wikipedia , lookup
History of RNA biology wikipedia , lookup
Vectors in gene therapy wikipedia , lookup
Human genome wikipedia , lookup
X-inactivation wikipedia , lookup
Gene expression programming wikipedia , lookup
Epigenetics of neurodegenerative diseases wikipedia , lookup
Epigenetics in learning and memory wikipedia , lookup
History of genetic engineering wikipedia , lookup
Genomic imprinting wikipedia , lookup
Polyadenylation wikipedia , lookup
Transcription factor wikipedia , lookup
Biology and consumer behaviour wikipedia , lookup
Genome evolution wikipedia , lookup
Point mutation wikipedia , lookup
Genome (book) wikipedia , lookup
Microevolution wikipedia , lookup
Minimal genome wikipedia , lookup
Polycomb Group Proteins and Cancer wikipedia , lookup
Short interspersed nuclear elements (SINEs) wikipedia , lookup
Non-coding RNA wikipedia , lookup
Designer baby wikipedia , lookup
Site-specific recombinase technology wikipedia , lookup
Ridge (biology) wikipedia , lookup
Nutriepigenomics wikipedia , lookup
Helitron (biology) wikipedia , lookup
Non-coding DNA wikipedia , lookup
Messenger RNA wikipedia , lookup
Long non-coding RNA wikipedia , lookup
Gene expression profiling wikipedia , lookup
Therapeutic gene modulation wikipedia , lookup
Epitranscriptome wikipedia , lookup
Artificial gene synthesis wikipedia , lookup
5/6/17 BIOLOGY 207 - Dr. Locke Lecture#7 - Eukaryote gene structure and regulation. Required readings and problems: Reading: Open Genetics, Chapter 12 Problems: Chapter 12 Optional Griffiths (2008) 9th Ed. Readings: pp 33-36, 385-402; 300-312 Problems: 9th Ed. Ch. 8: 2,3,6,8,12-14,18 Ch 11: 1,2,5,16 Campbell (2008) 9th Ed. Readings: Concept 17.1-3, 18.2 Concepts: How are eukaryote genes organized & regulated? 1. Higher Eukaryote genes are generally larger and more complex than those of Prokaryotes. 2. Their transcripts are processed in the nucleus before being exported to the cytoplasm, where they are translated. 3. Proteins interact with various DNA sequences to regulate gene expression. 4. Eukaryotic genes are regulated at the promoter, by enhancers/silencers, and by chromatin structure, too. Biol207 Dr. Locke section Lecture#7 Fall'11 page 1 5/6/17 The eukaryote genome contains various different types of sequences Types of sequences 1) Single copy genes - includes most protein coding genes 2) Multiple copy genes - e.g. rRNA, tRNA, some protein coding genes. 3) Repeated sequences. 3a Short centromeric - tandem array - clustered 3b SINES Short INterspersed ElementS (Alu element – lab #9) 3c LINES Long INterspersed ElementS 3d VNTR Variable Number Tandem Repeats Higher Eukaryotes have an excess of DNA - more than needed to code for protein encoding genes. - rest -> ???? - C-value paradox Junk DNA? -----------------------------------------O------------------------------------- Biol207 Dr. Locke section Lecture#7 Fall'11 page 2 5/6/17 Transcripts in Eukaryotes: Monocistronic and modified Steps in the processing of Eukaryote mRNA a. Transcript produced by RNA polymerase II (for mRNA) b. Addition of 7-methyl guanosine cap to 5' end c. Transcription past poly(A) site d. Endonuclease cleavage after AAUAAA signal sequence. e. Addition of poly(A) tail as series of 150-200 A by poly(A) polymerase f. Complete primary mRNA - not yet "mature" Introns and exons: Primary transcripts are shortened by removal of intervening sequences (introns) before transport to the cytoplasm. Fig Biol207 Dr. Locke section Lecture#7 Fall'11 page 3 5/6/17 Example: the ovalbumin gene/mRNA in chickens. 1- Primary transcript of ~7,700 bp has 5' cap and 3' poly A added, 2- The 7 introns (A-G) spliced out in a series of steps to produce a mature mRNA of 1872 nucleotides. 3- Regions L and 1-7 are called exons (vs. introns) and are joined together to form the mature mRNA. The biochemistry of intron splicing is well understood and involves the lariat model. For some genes (most) the processed mature mRNA is the same product each time. Biol207 Dr. Locke section Lecture#7 Fall'11 page 4 5/6/17 Alternative Splicing Some genes have primary transcripts that are processed to produce more than one type of mature mRNA - > more than one type of protein product The same primary transcript can be processed to yield different mRNAs, which encode different proteins. (Another means of gene regulation - post-transcriptional level) Example: Fig Rat -tropomyosin gene Note: 1- Tissue specific differences in expression 2- Alternate 5’ (transcription initiation sites) 3- Alternate 3’ ends ( poly A sites) 4- What does intron/exon mean? 5- Different genes have different levels of alternate splicing Biol207 Dr. Locke section Lecture#7 Fall'11 page 5 5/6/17 Eukaryote Regulation of Transcription In prokaryote genes: - positive and negative regulators that involve trans-acting factors (e.g. I gene-->lac operon) that act on cis-dominant regulatory sequences (e.g. operators or initiators, or binding sites in the promoter). In eukaryote genes: - also have trans-acting factors and cis-acting regulatory sequences Proximal cis-acting elements - The Promoter Region Fig beta-globin promoter Mutations have been used to define the essential promoter sequences. Many nucleotides can be changed with no effect on transcription. DNA sequences in the promoter region of the gene: |-----> mRNA - - - - GGGCGG- - - - - CCAAT - - - - - - - TATA - - - - - - - - - - - - - - - 110 -40 - 30 1 Three sequences are frequently found immediately upstream from the mRNA transcription start site. "TATA box" sequence serves to guide the RNA polymerase to begin transcription about 30 bp downstream at the start site. Biol207 Dr. Locke section Lecture#7 Fall'11 page 6 5/6/17 Distal elements - Enhancer sequences /silencers Enhancers (upstream activating sequences - UAS in yeast) are cis-acting sequences that can increase rates of transcription from an adjacent promoter on the same molecule (or chromosome). They can act at distances of many Kbp - upstream or downstream from the promoter that they affect several Kb |----> mRNA - - - - - - Enhancer - - - - - - - - - Promoter - - - - - - Example: Yeast Gal4 activation Fig Gal4- dimer - separate DNA binding and activation domains Binds to an enhancer to positively influence the adjacent genes promoter and increases transcription. Transcriptional activator proteins recuit the transcriptional machinery. Fig Bring RNA Pol II & other proteins to promoter to increase transcription. Enhancers, promoters and transacting factors, together, regulate transcription. Biol207 Dr. Locke section Lecture#7 Fall'11 page 7 5/6/17 Chromatin regulates gene expression Euchromatin - loosely packaged, accessible by transcription enzymes - gene expression is possible (but not obligatory) Heterochromatin - tightly packaged, inaccessible by transcription enzymes - gene expression is not possible (not permitted) Chromosome specific heterochromatinization. Human X-chromosome MALE : Y/X one X 1 copy of genes FEMALE: X/X two X 2 copies of genes -> need to compensate -> dosage compensation - 1 copy worth by X-chromosome inactivation (random) - X-chromosome wide repression - no genes expressed (almost none) - chromatin specific to that X is responsible. Biol207 Dr. Locke section Lecture#7 Fall'11 page 8 5/6/17 Inactivated chromatin structure of the X-chromosome is inherited in the daughter cells (epigenetics) Fig Both XM and XP are present in each female cell but one is inactivated during early development This random event becomes an inherited property of that chromosome, and all its daughter chromosomes are inactivated, too, even the cell is put into in vitro culture. Biol207 Dr. Locke section Lecture#7 Fall'11 page 9