chapter 11 mastering

Dark G bands that appear along chromosomes contain: heterochromatic regions. telomeres. euchromatic regions. centromeres.

heterochromatic regions

Where are you most likely to find histone protein ? in nucleosomes close to nucleosomes

in nucleosomes

Identify the ways in which telomeres and centromeres are similar. Telomeres and centromeres are primarily composed of facultative heterochromatin. are packaged into heterochromatin. rarely have expressed genes. serve the same functions.

- are packaged into heterochromatin. - rarely have expressed genes.

heterochromatin has

- few expressed genes - condensed chromatin

Euchormatin has

- less chromatin condensation - many expressed genes

Genomic DNA from the nematode worm Caenorhabditis elegans is organized by nucleosomes in the manner typical of eukaryotic genomes, with 145 bp encircling each nucleosome and approximately 55 bp in linker DNA. When C. elegans chromatin is carefully isolated, stripped of nonhistone proteins, and placed in an appropriate buffer, the chromatin decondenses to the 10-nm fiber structure. Suppose researchers mix a sample of 10-nm-fiber chromatin with a large amount of the enzyme DNase I that randomly cleaves DNA in regions that are not protected by bound protein. Next, they remove the nucleosomes, separate the DNA fragments by gel electrophoresis, and stain the fragments by ethidium bromide. 1 2 3 4

1

If the number of nucleosomes given in answer to part a of the Genetic Analysis is for the nucleus of a cell in , how many nucleosomes do you expect in the nucleus after completion of phase?

1.0×10^6

Genomic DNA from the nematode worm Caenorhabditis elegans is organized by nucleosomes in the manner typical of eukaryotic genomes, with 145 bp encircling each nucleosome and approximately 55 bp in linker DNA. When C. elegans chromatin is carefully isolated, stripped of nonhistone proteins, and placed in an appropriate buffer, the chromatin decondenses to the 10-nm fiber structure. Suppose researchers mix a sample of 10-nm-fiber chromatin with a large amount of the enzyme DNase I that randomly cleaves DNA in regions that are not protected by bound protein. Next, they remove the nucleosomes, separate the DNA fragments by gel electrophoresis, and stain the fragments by ethidium bromide. What size DNA fragment do you expect to see in the stained electrophoresis gel assuming all unprotected DNA was cleaved?

145

The bison genome contains base pairs. The length of linker DNA in mammals is 50 base pairs. Approximately how many nucleosomes are required to organize the 10-nm-fiber structure of the genome?

2.4×10^7 nucleosomes

Referring to the image, there appears to be a span of 13 "beads" present. Ignoring the DNA before the first bead and after the 13th bead, how much DNA is present in the photo?

2546 base pairs

Along a 6000-bp segment of DNA, approximately how many molecules of each kind of histone protein do you expect to find? H1, H2A, H2B, H3, H4 =

30, 60, 60, 60, 60

Under normal cellular conditions, what is the diameter of the chromatin as it forms the solenoid structure? 100 nm 30 nm 3 nm 34 nm 10 nm

30nm

How many total polypeptide chains would be present in a single nucleosome core particle?

8

What is the relative difference you expect between the levels of chromosome condensation in interphase and in metaphase? Interphase chromosomes will be less condensed than metaphase chromosomes. Interphase chromosomes will be more condensed than metaphase chromosomes. Interphase chromosomes will be as condensed as metaphase chromosomes

Interphase chromosomes will be less condensed than metaphase chromosomes

Are all of the additional nucleosomes that are present after completion of phase composed of newly synthesized histone proteins? Yes no

No

rt A A survey of organisms living deep in the ocean reveals two new species whose DNA is isolated for analysis. DNA samples from both species are treated to remove nonhistone proteins. Each DNA sample is then treated with micrococcal nuclease that cuts DNA not protected by proteins but is unable to cut DNA bound by histone proteins. Following micrococcal nuclease treatment, DNA samples are subjected to gel electrophoresis, and the gels are stained with ethidium bromide to stain all DNA bands in the gel. The ethidium bromide staining patterns of DNA from each species are shown in the figure. The number of base pairs (bp) in small DNA fragments is shown at the left of the gel. Choose the correct interpretation of the gel results in terms of the spacing of nucleosomes in the chromatin of each species. The nucleosome spacing in species A is 400 bp, whereas the spacing in species B is 800 bp. The nucleosome spacing in species A is 600 bp, whereas the spacing in species B is 400 bp. The nucleosome spacing in species A is 200 bp, whereas the spacing in species B is 400 bp. The nucleosome spacing in species A and B is 800 bp

The nucleosome spacing in species A is 200 bp, whereas the spacing in species B is 400 bp.

Chromatin structure is dynamic. In regions of highly condensed chromatin, such as the centromere, the boundary between heterochromatin and euchromatin is variable. Genes that are near this boundary region can be influenced by either type of chromatin in what is referred to as position effects. Recall the early Drosophila melanogaster experiments by Hermann Muller where the repositioning of the w + allele (normal activity of the w + allele produces red eye pigment) by translocation or inversion near this boundary of chromatin produced intermittent w + activity. In the heterozygous state (w +/w), a variegated eye is produced, with white and red patches. When heterochromatin spreading encompasses the new location of w + allele, the gene is not transcribed, producing white eye patches. Since the genotype is heterozygous, half of the cells will receive the w + allele producing red eye patches, while the other half will receive the w allele producing white patches. When heterochromatin spreading does not reach the new location of the w + allele, the gene will be transcribed, producing red eye patches. Even though eye color phenotypic variegation exists within the eye, all cells have the same genotype. When heterochromatin spreading encompasses the new location of w + allele, the gene is transcribed, producing white eye patches

When heterochromatin spreading encompasses the new location of w + allele, the gene is not transcribed, producing white eye patches. When heterochromatin spreading does not reach the new location of the w + allele, the gene will be transcribed, producing red eye patches. Even though eye color phenotypic variegation exists within the eye, all cells have the same genotype.

Mammals with multiple X chromosomes undergo random X-inactivation in each nucleus early in gestational development. This results in only one X chromosome being active in each cell, no matter how many X chromosomes are present. Which sex chromosome genotype(s) would you expect to express Xist RNA? XX XXXX XY XXXY

XX, XXXX, XXXY

Mammals with multiple X chromosomes undergo random X-inactivation in each nucleus early in gestational development. This results in only one X chromosome being active in each cell, no matter how many X chromosomes are present. Which noncoding RNA coats the inactive X-chromosome in regions of heterochromatin? tRNA Xist RNA HP-1 RNA 5S rRNA

Xist RNA

which of the following are examples of heterochromatin? repetitive DNA Barr body centromeric DNA telomeric DNA

all

Light G bands that appear along chromosomes contain: heterochromatic regions. telomeres. euchromatic regions. centromeres.

euchromatic regions

Mammals with multiple X chromosomes undergo random X-inactivation in each nucleus early in gestational development. This results in only one X chromosome being active in each cell, no matter how many X chromosomes are present. In general, which of the following would be consistent with an X chromosome bound by Xist RNA? reduced gene expression Xist RNA expression histone acetylation heterochromatic histone methylation decondensed chromatin histone deacetylation

reduced gene expression, Xist RNA expression, heterochromatic, histone methylation, histone deacetylation

what are the two principal mechanisms of bacterial DNA compaction?

supercoiling and folding into loops

Assume that the DNA associated with a nucleosome core particle plus the DNA in the linker adds up to 200 bp. Approximately how many base pairs are found in the linker region?

~54