19.1 1. Describe the structure of a nucleosome, the basic unit of DNA packaging in eukaryotic cells.
19.1 • 1. • Eight histone proteins (2 each of 4 different kinds) • DNA wound around them • Linker DNA between histones
19.1 2. What chemical properties of histones and DNA enable these molecules to bind tightly together?
19.1 • 2. • Histones contain many basic amino acids with + charges • Phosphate groups in DNA’s backbone are negatively charged
19.1 3. In general, how does dense packing of DNA in chromosomes prevent gene expression?
19.1 3. RNA polymerase cannot physically get at the DNA
19.2 1. In general, what is the effect of histone acetylation and DNA methylation on gene expression?
19.2 • 1. • Histone acetylation usually flags genes for expression • DNA methylation usually flags them for not being expressed
19.2 2. Compare the roles of general and specific transcription factors in regulating gene expression.
19.2 2. General transcription factors Assemble transcription initiation complex for promoters of all genes Specific transcription factors Bind to control elements for just one gene and either activate or repress it
19.2 3. 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?
19.2 • 3. • 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
19.2 4. 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?
19.2 4. Degradation of mRNA Regulation of translation Activation of protein Degradation of protein
19.3 1. Compare the usual functions of proteins encoded by proto-oncogenes with those encoded by tumor-suppressor genes.
19.3 • 1. • Product of proto-oncogene stimulates cell division • Product of tumor-suppressor gene inhibits cell division
19.3 2. Explain how the types of mutations that lead to cancer are different for a proto-oncogene and a tumor-suppressor gene.
19.3 • 2. • Mutation of proto-oncogene makes overactive protein • Product of tumor-suppressor makes inactive protein
19.3 3. Under what circumstances do we consider cancer to have a hereditary component?
19.3 3. • Oncogenes • Mutant alleles of tumor-supressor genes
19.4 1. Discuss the characteristics that make mammalian genomes larger than prokaryotic genomes.
19.4 • 1. • 5x – 15x more genes • 10,000x more non-coding DNA • Introns make genes 27% longer on average
19.4 2. How do introns, transposable elements, and simple sequence DNA differ in their distribution in the genome?
19.4 2. • Introns are within coding regions of genes • Transposable elements are scattered throughout • Simple sequence DNA is mostly at telomeres and centromeres
19.4 3. Discuss the differences in the organization of the rRNA gene family and the globin gene families. How do these gene families benefit the organism?
19.4 3. • Globin • Many non-identical genes near each other • Different genes means different kinds of globin can be made at different stages of development • rRNA • Many indentical genes in tandem • Lots of genes means lots of rRNA can be made
19.5 1. Describe three examples of errors in cellular processes that lead to DNA duplications.
19.5 1. Faulty cytokinesis can make two entire copies of genome Errors in crossing over Backward slippage during DNA replication copies some of it twice
19.5 2. What processes are thought to have led to the evolution of the globin gene families?
19.5 2. • Gene duplication • Divergence by mutation • Movement of genes to different chromosomes
19.5 3. Look at the portions of the fibronectin and EGF genes shown in the figure below. How might they have arisen?
19.5 3. Errors in crossing over
19.5 4. What are three ways transposable elements are thought to contribute to the evolution of the genome?
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