m44,45 - ebnalfady

[ArchivalUser]

44. The consensus sequence 5² TATAAAA 3² found in eukaryotic genes is quite similar to a consensus sequence observed in prokaryotes. It is impor¬tant as the
a. Only site of binding of RNA polymerase III
b. Promoter for all RNA polymerases
c. Termination site for RNA polymerase II
d. Major binding site of RNA polymerase I
e. First site of binding of a transcription factor for RNA polymerase II

45. The so-called caps of RNA molecules
a. Allow tRNA to be processed
b. Occur at the 3² end of tRNA
c. Are composed of poly A
d. Are unique to eukaryotic mRNA
e. Allow correct translation of prokaryotic mRNA

[ArchivalUser]

44e 45d

[ArchivalUser]

e
d

[ArchivalUser]

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44.
The answer is e.
The first event that occurs in mRNA synthesis is the binding of transcription factor TFIID to the TATA box. This consensus sequence portion of virtually all eukaryotic genes coding for mRNA is cen­tered at about .25 and is similar to a 10-sequence promoter box found in prokaryotes. TFIID contains a TATA box“binding protein. The following sequence occurs in the initiation of mRNA synthesis:


1.
TFIID binding to the TATA box

2.
TFIIA binding

3.
TFIIB binding

4.
RNA polymerase II binding

5.
TFIIE binding


When all these elements are bound to DNA, the basal transcription appa­ratus complex is formed and can transcribe DNA slowly. Other factors are required for fast, efficient mRNA synthesis.
45. The answer is d.
The primary transcripts of all eukaryotic mRNAs are capped at the 5. end. Prokaryotic RNAs and eukaryotic tRNA and rRNA are not capped. The cap is composed of 7-methylguanylate attached by a pyrophosphate linkage to the 5. end. This is known as cap 0. One of the adjacent riboses is methylated in cap 1, and both of the adjacent riboses are methylated in cap 2. The cap protects the 5. ends of mRNAs from nucleases and phosphatases and is essential for the recognition of eukaryotic mRNAs in the protein-synthesizing system. When prokaryotic monocistronic mRNAs are artificially capped, translation occurs in a eukaryotic, in vitro translation system.

[ArchivalUser]

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