The DNA of gene X in humans has been isolated, cloned, and sequenced and is 8000 base pairs in length. From cells that were actively transcribing gene X, a cDNA library was made. In this case, gene X was found to produce from an mRNA that was 4200 bases in length. The most probable explanation of these results is that
A) there was no mRNA in the cells of the mRNA used to make the cDNA library.
B) the DNA encoded introns that were excised during mRNA processing.
C) a mutation resulted in a large loss of this particular gene.
D) reverse transcription of the mRNA isolate was not complete.
E) none of the above
B) the DNA encoded introns that were excised during mRNA processing.
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Fleas
A. may transmit Yersinia pestis. B. may transmit Lyme disease. C. may transmit a toxin. D. have only one host, humans.
Since many childhood diseases such as mumps and measles are rare now within the United States, why is it still important for children to be immunized against them?
A. If we lose herd immunity by removing mandatory vaccination, our population will become susceptible to these illnesses again in a short period of time. B. There is always the likelihood that an individual from another country could import one of these illnesses into the United States, sparking an outbreak of new infections, if we aren't all properly vaccinated. C. By keeping the population vaccinated, we keep incidence rates of these illnesses very low. This helps to protect people that cannot be vaccinated (very young children, pregnant women, immunocompromised individuals, the elderly). D. Many of these diseases are HIGHLY contagious, and commonly through respiratory droplet (airborne) transmission. This makes an outbreak within a susceptible population very possible. Keeping the population resistant through mandatory vaccination prevents this possibility. E. All of the options are correct.
Under which of the following conditions would you expect to find a cell with a predominance of free ribosomes?
a. a cell that is secreting proteins b. a cell that is producing cytoplasmic enzymes c. a cell that is constructing its cell wall or extracellular matrix d. a cell that is digesting food particles e. a cell that is enlarging its vacuole
How do prions, which are misfolded proteins, infect organisms?
a) Prions only arise through spontaneous mutation. They are not transmissible. b) Prions recruit ribosomes to make more copies of the wrong form of the protein. c) Prions enter brain cells and cause normal forms of the protein to refold into the prion form. d) Prions enter brain cells through the lymphatic system and make copies of themselves. e) None of the above.