Chapter 19 Organization and Control of Eukaryotic Genomes …Or How To Fit All of the Junk In the Trunk

Eukaryotic Chromatin Structure Order of Chromatin Structure Order of Chromatin Structure DNA double helix DNA double helix Nucleosomes Nucleosomes 30-nm chromatin fiber 30-nm chromatin fiber Looped domains Looped domains Folding of looped domains Folding of looped domains

Details, Details, Details Nucleosomes are made up of four Histones. H2A, H2B, H3, H4 Nucleosomes are made up of four Histones. H2A, H2B, H3, H4 Histones are mostly postitivly charged amino acids. Histones are mostly postitivly charged amino acids. DNA (negitivly charged is attracted to Histones) DNA (negitivly charged is attracted to Histones) DNA is wrapped around the Nucleosomes twice. An extra Histone (H1) Binds to the DNA just after the Nucleosome. DNA is wrapped around the Nucleosomes twice. An extra Histone (H1) Binds to the DNA just after the Nucleosome.

Figure 3-D-2. Each nucleosome consists of 146 bp DNA and 8 histones: two copies for each of H2A, H2B, H3 and H4. The DNA is wrapped around the histone core, making nearly two turns per nucleosome. Figure 3-D-2. Each nucleosome consists of 146 bp DNA and 8 histones: two copies for each of H2A, H2B, H3 and H4. The DNA is wrapped around the histone core, making nearly two turns per nucleosome.

Even More Details! 30-nm Chromatin fiber—Coils of the Fiber with the Nucleosome that forms folds that are 30 nm in size 30-nm Chromatin fiber—Coils of the Fiber with the Nucleosome that forms folds that are 30 nm in size Looped domains—30nm fiber folds and attaches on to nonhistone protein scafold. Looped domains—30nm fiber folds and attaches on to nonhistone protein scafold. When Chromatin is condensed into chromosomes the looped domains coil and form a tightly packed Chromosome. When Chromatin is condensed into chromosomes the looped domains coil and form a tightly packed Chromosome.

Genome Organization at the DNA Level Repetitive DNA (non-coding) Repetitive DNA (non-coding) Accounts for aprox 97% of human DNA Accounts for aprox 97% of human DNA Tandemly Repetitive DNA—Short sequences repeted in a series. Tandemly Repetitive DNA—Short sequences repeted in a series. Can cause Genetic disorders. Can cause Genetic disorders. Typically found in centromeres and telomeres so it is thought to be used for structure. Typically found in centromeres and telomeres so it is thought to be used for structure. Interspersed Repetitive DNA—Copies of similar sequences but not repetitive. Interspersed Repetitive DNA—Copies of similar sequences but not repetitive.

Gene Change in Somatic Cells Gene Amplification—Selective replication of specific genes. Gene Amplification—Selective replication of specific genes. Example in egg cells increasing the amount of rRNA will increase the number of ribosomes which increases the protein output of the cell when it is fertilized. Example in egg cells increasing the amount of rRNA will increase the number of ribosomes which increases the protein output of the cell when it is fertilized. Transposons and Retrotransposons— DNA that can move from one location to another. RT utilizes RNA and reverse transcriptase to move. Transposons and Retrotransposons— DNA that can move from one location to another. RT utilizes RNA and reverse transcriptase to move.

Gene Expression Specialized Cells and tissues are selective in the genes they express. Genes turned on and off in response to signals. Specialized Cells and tissues are selective in the genes they express. Genes turned on and off in response to signals. Pg 363 to see general overview of gene expression. Pg 363 to see general overview of gene expression.

Chromatin Modifications Chromatin Modifications affect the gene availability for transcription Chromatin Modifications affect the gene availability for transcription DNA Methylation—Attachment of methyl groups (CH3) to DNA bases after DNA synthesis. DNA Methylation—Attachment of methyl groups (CH3) to DNA bases after DNA synthesis. Inactive DNA is usually highly methylated when compared to highly active transcription regions of DNA. Inactive DNA is usually highly methylated when compared to highly active transcription regions of DNA.

More Modifications Histone Acetylation—attachement of Acetyl groups (COCH3) to amino acids of histone groups. Deacetylation is the removal of acetyl groups from histones. Histone Acetylation—attachement of Acetyl groups (COCH3) to amino acids of histone groups. Deacetylation is the removal of acetyl groups from histones. Histones that have been acelylated have a looser bond with DNA and transcription proteins have easier access to DNA. Histones that have been acelylated have a looser bond with DNA and transcription proteins have easier access to DNA.

Left for you Control elements and transcription factors pg Control elements and transcription factors pg Biology of Cancer pg Biology of Cancer pg