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Transcription in Eukaryotes

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1. a. What unit is considered to compose the first order of chromatin folding in eukaryotes?
b. Define the terms "heterochromatin" and "euchromatin."
c. Why is transcription control necessary in eukaryotes?
2. a. List the three types of RNA polymerase enzyme, and for each, give the RNA molecule type it produces.
b. What are the three components of a preinitiation complex?
c. Describe the promoter sequence recognized by RNA polymerase II. Why might it be more complex than the other two promoters?
3. Take any RNA polymerase and describe the sequence of events of transcription of a specific DNA sequence. Include the assembly of the preiniation complex through elongation to termination.
4. a. Describe two post-transcriptional mechanisms.
b. What is the purpose of such mechanisms?
c. What is R-looping?
5. Consider the whole process of transcription in both eukaryotes and prokaryotes. Compare and contrast the two mechanisms in detail.

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1. a. What unit is considered to compose the first order of chromatin folding in eukaryotes? The first order of chromatin folding in eukaryotes is called the "nucleosome." The nucleosome core particle consists of approximately 147 base pairs of DNA wrapped almost twice (1.65 superhelical turns) around a histone octamer consisting of 2 copies each of the core histones H2A, H2B, H3 and H4.
http://www.accessexcellence.org/RC/VL/GG/nucleosome.php
b. Define the terms "heterochromatin" and "euchromatin." Heterochromatin is chromosomal material that is darkly staining and tightly coiled throughout the cell cycle and that is, for the most part, genetically inactive. Euchromatin is a lightly packed form of chromatin encoding for many genes and is often being actively transcribed. Euchromatin is found in both eukaryotes and prokaryotes.
c. Why is transcription control necessary in eukaryotes? Transcription control is necessary in eukaryotes because this process is used to copy specific genes for specific functions. Transcription for these organisms requires some energy, and this is energy cells do not want to waste. It is important that transcription is completed correctly, producing mRNA products that are functional and not mutated. If an mRNA product is mutated, it is degraded and essentially "wasted." A mutated mRNA could be translated, creating a mutated protein. Stopping mutation is important in eukaryotes, which are mostly multi-celled organisms. Prokaryotes, or single-celled organisms, do not need to put as much effort into controlling transcription. Eukaryotes have multiple control check-points for the transcription process.
2. a. List the three types of RNA polymerase enzyme, and for each, give the RNA molecule type it produces. Eukaryotes have three RNA polymerase enzymes, named RNA polymerase I, RNA polymerase II, and RNA polymerase III. RNA polymerase I makes pre-rRNA, which will eventually mature into the 28S, 18S, and 5.8S rRNA subunits that make up a ribosome. RNA polymerase II makes mRNA precursors, as well as microRNSa and snRNAs. RNA polymerase III makes ...

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The expert examines transcription in eukaryotes.

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