BS120 CHAPTER 19

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Information about BS120 CHAPTER 19
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Published on October 16, 2007

Author: Woodwork

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Chapter 19:  Chapter 19 Eukaryotic Genomes Organization, Regulation, and Evolution Figure 19.1 DNA in a eukaryotic chromosome from a developing salamander egg:  Figure 19.1 DNA in a eukaryotic chromosome from a developing salamander egg Figure 19.2 Levels of chromatin packing:  Figure 19.2 Levels of chromatin packing Mitotic chromosome vs. Interphase chromosome. Interphase chromatin is generally much less condensed Interphase chromosomes have highly condensed areas, heterochromatin, and less compacted areas, euchromatin. Figure 19.3 Stages in gene expression that can be regulated in eukaryotic cells:  Figure 19.3 Stages in gene expression that can be regulated in eukaryotic cells Figure 19.4 A simple model of histone tails and the effect of histone acetylation:  Figure 19.4 A simple model of histone tails and the effect of histone acetylation Methylation and genomic imprinting. Inheritance of traits by mechanisms not directly involving the nucleotide sequence is called epigenetic inheritance. Histones leave the DNA only transiently during DNA replication. They stay with the DNA during transcription. The members of the histone deacetylase (HDAC) family play important roles in various cellular processes, including transcriptional regulation, cell proliferation, differentiation and apoptosis. Inhibitors of histone deacetylases are emerging as an important new class of chemotherapeutic agents. As such, identifying stable and potent chemical HDAC inhibitory compounds is an important focus for translational research. Figure 19.5 A eukaryotic gene and its transcript:  Figure 19.5 A eukaryotic gene and its transcript These modifications seem to facilitate the export of mRNA from the nucleus. They help protect mRNA from hydrolytic enzymes. They help the ribosomes attach to the 5’ end of the mRNA. Figure 19.6 A model for the action of enhancers and transcription activators:  Figure 19.6 A model for the action of enhancers and transcription activators combination of control elements Eukaryotic genes also have repressor proteins Slide8:  The transcription process as depicted by Roger Kornberg (Nobel prize in 2006, Chemistry) RNA-polymerase in white, DNA-helix in blue and the growing RNA-strand in red. Figure 19.7 Cell type–specific transcription:  Figure 19.7 Cell type–specific transcription Cis-regulatory element (a DNA sequence) vs. trans-regulatory element (proteins) cellular differentiation, the divergence in form and function as cells in a multicellular organism specialize. Totipotent stem cells Figure 19.8 Alternative RNA splicing:  Figure 19.8 Alternative RNA splicing Figure 19.9 Regulation of gene expression by microRNAs (miRNAs):  Figure 19.9 Regulation of gene expression by microRNAs (miRNAs) Slide12:  The short RNA fragments are known as small interfering RNA (siRNA) when they derive from exogenous sources and microRNA (miRNA) when they are produced from RNA-coding genes in the cell's own genome. The phenomenon of inhibition of gene expression by RNA molecules is called RNA interference (RNAi). may have originated as a natural defense against infection by RNA viruses. Small single-stranded RNA molecules called microRNAs, or miRNAs, that bind to complementary sequences in mRNA molecules; to break down or inhibit translation. Slide13:  RNA interference. Nobel Prize in 2006 Craig C. Mello, born 1960, University of Massachusetts Medical School, Worcester, MA, USA. Andrew Z. Fire, born 1959, Stanford University School of Medicine, Stanford, CA, USA. Potent and specific genetic interference by double-stranded RNA in Caenorhabditis elegans. Nature. 1998 Feb 19;391(6669):806-11. Slide14:  Figure 1. Phenotypic effect after injection of single-stranded or double-stranded unc-22 RNA into the gonad of C. elegans. The unc-22 gene encodes a myofilament protein. Decrease in unc-22 activity is known to produce severe twitching movements. Injected double-stranded RNA, but not single-stranded RNA, induced the twitching phenotype in the progeny. Figure 19.10 Degradation of a protein by a proteasome:  Figure 19.10 Degradation of a protein by a proteasome Many proteins, like the cyclins in the cell cycle, must be short-lived to function appropriately. Slide16:  Ubiquitin-mediated protein degradation The Nobel Prize in Chemistry 2004 Aaron Ciechanover, Avram Hershko and Irwin Rose Figure 19.11 Genetic changes that can turn proto-oncogenes into oncogenes:  Figure 19.11 Genetic changes that can turn proto-oncogenes into oncogenes Cancer-causing genes, oncogenes, were initially discovered in retroviruses, but close counterparts, proto-oncogenes, have been found in other organisms. The products of proto-oncogenes are proteins that stimulate normal cell growth and division and play essential functions in normal cells. Slide18:  David Baltimore Renato Dulbecco Howard Temin Harold Varmus Michael Bishop Nobel Prize in 1989 Nobel Prize in 1975 the interaction between tumour viruses and the genetic material of the cell discovered reverse transcriptase upset the widely held belief at the time of the "Central Dogma" of molecular biology posited by Nobel laureate Francis Crick the cellular origin of retroviral oncogenes. Viruses, especially retroviruses, play a role in about 15% of human cancer cases worldwide. i.e. papillomavirus (HPV, cervical cancer) Figure 19.12 Signaling pathways that regulate cell division:  Figure 19.12 Signaling pathways that regulate cell division proto-oncogenes are proteins that stimulate normal cell growth and division and play essential functions in normal cells. tumor-suppressor proteins inhibit cell division Figure 19.13 A multistep model for the development of colorectal cancer:  Figure 19.13 A multistep model for the development of colorectal cancer predispositions to cancer that run in some families APC is mutated in about 60% of colorectal cancers. one mutant BRCA1 allele (a tumor suppressor gene) has a 60% probability of developing breast cancer before age 50 Figure 19.14 Types of DNA sequences in the human genome:  Figure 19.14 Types of DNA sequences in the human genome Centromeres and telomeres Figure 19.15 The effect of transposable elements on corn kernel color:  Figure 19.15 The effect of transposable elements on corn kernel color Figure 19.16 Movement of eukaryotic transposable elements:  Figure 19.16 Movement of eukaryotic transposable elements Figure 19.17 Gene families:  Figure 19.17 Gene families higher affinity for oxygen Figure 19.18 Gene duplication due to unequal crossing over:  Figure 19.18 Gene duplication due to unequal crossing over Figure 19.19 Evolution of the human -globin and -globin gene families:  Figure 19.19 Evolution of the human -globin and -globin gene families The necessary function provided by an a-globin protein was fulfilled by one gene, while other copies of the a-globin gene accumulated random mutations. Table 19.1 Percentage of Similarity in Amino Acid Sequence Between Human Globin Proteins:  Table 19.1 Percentage of Similarity in Amino Acid Sequence Between Human Globin Proteins Figure 19.20 Evolution of a new gene by exon shuffling:  Figure 19.20 Evolution of a new gene by exon shuffling Mixing and matching of different exons within or between genes owing to errors in meiotic recombination is called exon shuffling

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