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19.11.Describe the structure of a nucleosome, the basic unit of DNA packaging in eukaryotic cells.
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19.11.•Eight histone proteins (2 each of 4 different kinds)•DNA wound around them•Linker DNA between histones
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19.12.What chemical properties of histones and DNA enable these molecules to bind tightly together?
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19.12.•Histones contain many basic amino acids with + charges•Phosphate groups in DNA’s backbone are negatively charged
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19.13.In general, how does dense packing of DNA in chromosomes prevent gene expression?
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19.13.RNA polymerase cannot physically get at the DNA
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19.21.In general, what is the effect of histone acetylation and DNA methylation on gene expression?
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19.21.•Histone acetylation usually flags genes for expression•DNA methylation usually flags them for not being expressed
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19.22.Compare the roles of general and specific transcription factors in regulating gene expression.
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19.22.General transcription factorsAssemble transcription initiation complex for promoters of all genes
Specific transcription factorsBind to control elements for just one gene and either activate or repress it
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19.23.If you compared the nucleotide sequences of the distal control elements in the enhancers of three coordinately regulated genes, what would you expect to find? Why?
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19.23.•All three genes have very similar sequences in the control elements of their enhancers•That way, the same specific transcription factors can bind to all three
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19.24.Once mRNA encoding a particular protein reaches the cytoplasm, what are four mechanisms that can regulate the amount of the active protein in the cell?
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19.24.
1.Degradation of mRNA2.Regulation of translation3.Activation of protein4.Degradation of protein
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19.31.Compare the usual functions of proteins encoded by proto-oncogenes with those encoded by tumor-suppressor genes.
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19.31.•Product of proto-oncogene stimulates cell division•Product of tumor-suppressor gene inhibits cell division
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19.32.Explain how the types of mutations that lead to cancer are different for a proto-oncogene and a tumor-suppressor gene.
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19.32.•Mutation of proto-oncogene makes overactive protein•Product of tumor-suppressor makes inactive protein
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19.33.Under what circumstances do we consider cancer to have a hereditary component?
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19.33.•Oncogenes•Mutant alleles of tumor-supressor genes
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19.41.Discuss the characteristics that make mammalian genomes larger than prokaryotic genomes.
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19.41.•5x – 15x more genes•10,000x more non-coding DNA•Introns make genes 27% longer on average
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19.42.How do introns, transposable elements, and simple sequence DNA differ in their distribution in the genome?
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•Introns are within coding regions of genes•Transposable elements are scattered throughout•Simple sequence DNA is mostly at telomeres and centromeres
19.42.
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19.43.Discuss the differences in the organization of the rRNA gene family and the globin gene families. How do these gene families benefit the organism?
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19.43.
rRNA•Many indentical genes in tandem•Lots of genes means lots of rRNA can be made
Globin•Many non-identical genes near each other•Different genes means different kinds of globin can be made at different stages of development
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19.51.Describe three examples of errors in cellular processes that lead to DNA duplications.
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19.51.1.Faulty cytokinesis can make two entire copies of genome2.Errors in crossing over 3.Backward slippage during DNA replication copies some of it twice
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19.52.What processes are thought to have led to the evolution of the globin gene families?
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19.52.•Gene duplication•Divergence by mutation•Movement of genes to different chromosomes
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19.5 3.Look at the portions of the fibronectin and EGF genes shown in the figure below. How might they have arisen?
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19.53.Errors in crossing over
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19.54.What are three ways transposable elements are thought to contribute to the evolution of the genome?
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19.5 4.•Scattered homologous transposons allow recombination between chromosomes•Transposons in regulatory areas change expression of genes•Transposons carry genes to new places in genome•Transposons carry exons , making new functional domains in existing genes