Which of the following statements about nucleosomes is true?
(a) Nucleosomes activate transcription when bound to the promoter.
(b) Although RNA polymerase can access DNA packed within nucleosomes, the general transcription factors and transcriptional regulators cannot.
(c) Histone acetyltransferases affect transcription by both altering chromatin structure to allow accessibility to the DNA and by adding acetyl groups to histones that can bind proteins that promote transcription.
(d) Histone deacetylases remove lysines from histone tails.
Choice (c) is correct. The binding of nucleosomes to the promoter inhibits transcription [choice (a)] by blocking RNA polymerase, the general transcription factors, and transcriptional regulators from accessing the DNA [choice (b)]. Histone deacetylases remove acetyl groups that are attached to lysines in the tail of histone proteins [choice (d)].
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Spontaneous generation _____
A) was demonstrated to occur under normal laboratory conditions by Pasteur B) apparently occurred at least onceâ€"when life on Earth began C) occurs every time a new species evolves from a preexisting species D) addresses the formation of new cells from existing cells
M-phase is regulated by M-phase cyclin-dependent kinase (CDK) and cyclin B1
a. true b. false
You notice mayfly larvae trying to emerge from a stream being slowed down when they reach the surface. Why might this be?
A) Because of the surface tension of the water. B) Because of the colder temperature at surface. C) Because of less oxygen at the surface. D) Because of higher flows at surface.
Which of the following best describes the sex chromosomes?
a. They are non-homologous. b. They are completely homologous. c. They are heterozygous. d. They are partially homologous, but also have unique regions.