Presentation on theme: "19.1 1. Describe the structure of a nucleosome, the basic unit of DNA packaging in eukaryotic cells."— Presentation transcript:
1 19.11.Describe the structure of a nucleosome, the basic unit of DNA packaging in eukaryotic cells.
2 19.11.Eight histone proteins (2 each of 4 different kinds)DNA wound around themLinker DNA between histones
3 19.12.What chemical properties of histones and DNA enable these molecules to bind tightly together?
4 19.12.Histones contain many basic amino acids with + chargesPhosphate groups in DNA’s backbone are negatively charged
5 19.13.In general, how does dense packing of DNA in chromosomes prevent gene expression?
6 19.13.RNA polymerase cannot physically get at the DNA
7 19.21.In general, what is the effect of histone acetylation and DNA methylation on gene expression?
8 19.21.Histone acetylation usually flags genes for expressionDNA methylation usually flags them for not being expressed
9 19.22.Compare the roles of general and specific transcription factors in regulating gene expression.
10 General transcription factors 19.22.General transcription factorsAssemble transcription initiation complex for promoters of all genesSpecific transcription factorsBind to control elements for just one gene and either activate or repress it
11 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?
12 19.23.All three genes have very similar sequences in the control elements of their enhancersThat way, the same specific transcription factors can bind to all three
13 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?
14 19.24.Degradation of mRNARegulation of translationActivation of proteinDegradation of protein
15 19.31.Compare the usual functions of proteins encoded by proto-oncogenes with those encoded by tumor-suppressor genes.
16 19.31.Product of proto-oncogene stimulates cell divisionProduct of tumor-suppressor gene inhibits cell division
17 19.32.Explain how the types of mutations that lead to cancer are different for a proto-oncogene and a tumor-suppressor gene.
18 19.32.Mutation of proto-oncogene makes overactive proteinProduct of tumor-suppressor makes inactive protein
19 19.33.Under what circumstances do we consider cancer to have a hereditary component?
20 19.33.OncogenesMutant alleles of tumor-supressor genes
21 19.41.Discuss the characteristics that make mammalian genomes larger than prokaryotic genomes.
22 19.41.5x – 15x more genes10,000x more non-coding DNAIntrons make genes 27% longer on average
23 19.42.How do introns, transposable elements, and simple sequence DNA differ in their distribution in the genome?
24 19.4 2. Introns are within coding regions of genes Transposable elements are scattered throughoutSimple sequence DNA is mostly at telomeres and centromeres
25 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?
26 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 developmentrRNAMany indentical genes in tandemLots of genes means lots of rRNA can be made
27 19.51.Describe three examples of errors in cellular processes that lead to DNA duplications.
28 19.51.Faulty cytokinesis can make two entire copies of genomeErrors in crossing overBackward slippage during DNA replication copies some of it twice
29 19.52.What processes are thought to have led to the evolution of the globin gene families?
30 19.52.Gene duplicationDivergence by mutationMovement of genes to different chromosomes
31 Look at the portions of the fibronectin and EGF genes shown in the figure below. How might they have arisen?
33 19.54.What are three ways transposable elements are thought to contribute to the evolution of the genome?
34 Scattered homologous transposons allow recombination between chromosomesTransposons in regulatory areas change expression of genesTransposons carry genes to new places in genomeTransposons carry exons , making new functional domains in existing genes