Describe the process of mRNA splicing
What will be an ideal response?
First, snRNPs bind with sequences at the junctions of each intron and exon. These snRNPs at the
borders of an intron associate with each other and others form a complex that loops out the intron.
Other snRNPs are also recruited to the complex. The active spliceosome then cuts the beginning of the
intron, and the intron bonds to itself. The spliceosome then cuts the intron at its end and joins together
the exons that were on either side of the intron. The intron is released and later degraded. Meanwhile,
the spliceosome disassembles as the snRNPs are released. When all introns are removed and all exons
joined together the mRNA is finished and ready for translation.
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One strain of rII- phage has a deletion in the rII region, another has a point mutation in the rII region. When E. coli K(?) cells are infected with either rII- phage (not both) no plaques form. When E. coli K(?) cells are infected with both rII- phage simultaneously plaques do form. Why do plaques form when E. coli K(?) cells are infected with both types of rII- phage simultaneously?
A) Recombination between the two phage genomes resulted in a wild-type phage. B) The two phage have mutations in different rII genes and their genomes complement each other. C) A protein made by the deletion phage can repair the DNA of the phage with the point mutation. D) Bacteria can survive infection with one phage, but they cannot survive infection with two phages.
What best describes index fossils?
a. Organisms that existed over a limited period b. Organisms whose age is hard to detect c. Fossils that are used in radioactive dating d. Fossils of the most ancient organisms
Flowering plants appeared in the fossil record in the:a
Cenozoic era. b. Late Cretaceous period. c. Paleozoic era. d. Jurassic and Lower Cretaceous periods. e. Tertiary period.
All protists are _____.
A. eukaryotic B. unicellular C. monophyletic D. symbionts E. mixotrophic