A gene that codes for a protein was removed from a eukaryotic cell and inserted into a prokaryotic cell. Although the gene was successfully transcribed and translated, it produced a different protein than it produced in the eukaryotic cell. What is the most likely explanation?
A. There are slight differences in the genetic code for prokaryotes and eukaryotes.
B. Unlike eukaryotes, which have three different RNA polymerases, prokaryotes have a single RNA polymerase.
C. Eukaryotic genes often contain introns while prokaryotic genes do not.
D. Eukaryotic transcripts have a 5' cap while prokaryotic transcripts do not.
Clarify Question
· What is the key concept addressed by the question?
· What type of thinking is required?
· What key words does the question contain and what do they mean?
Gather Content
· What do you already know about transcription and translation?
Consider Possibilities
· Consider the different answer options. Which can you rule out?
Choose Answer
· Given what you now know, what information and/or problem solving approach is most likely to produce the correct answer?
Reflect on Process
· Did your problem-solving process lead you to the correct answer? If not, where did the process break down or lead you astray? How can you revise your approach to produce a more desirable result?
C. Eukaryotic genes often contain introns while prokaryotic genes do not.
Clarify Question
· What is the key concept addressed by the question?
o This question addresses transcription and translation.
· What type of thinking is required?
o This question is asking you to analyze the information given, using logic, to dissect the problem and determine the answer.
· What key words does the question contain and what do they mean?
o A eukaryotic cell is from an organism with a nucleus, like a human, fly, plant, or fungus.
o A prokaryotic cell is a single-celled organism such as a bacterium like E. coli.
Gather Content
· What do you already know about transcription and translation?
o There are some key differences in transcription and translation between eukaryotes and prokaryotes.
o One of the main differences is that eukaryotic genes typically have introns, which are spliced out of the pre-mRNA by specialized splicing machinery. Prokaryotes do not have introns or the machinery to splice them out.
Consider Possibilities
· Consider the different answer options. Which can you rule out?
o Could the different RNA polymerases explain the change in the protein? No, that doesn’t make sense.
o Could the 5’ cap explain the change in the protein? No, because that affects stability but not the sequence of the protein itself.
Choose Answer
· Given what you now know, what information and/or problem solving approach is most likely to produce the correct answer?
o The best explanation is that the eukaryotic gene contained introns. In a prokaryote they would not be removed, so the protein would have extra sections of translated sequence.
o For this reason, scientists usually use a cDNA, or complementary DNA copy from a processed mRNA, rather than the DNA gene itself when they clone a eukaryotic gene into bacteria for protein expression.
Reflect on Process
· Did your problem-solving process lead you to the correct answer? If not, where did the process break down or lead you astray? How can you revise your approach to produce a more desirable result? o This question asked why a eukaryotic gene would not produce the same protein in a prokaryote.
o The question required you to analyze the information given, using logic, to dissect the problem and determine the answer.
o Did you recognize that prokaryotes lack the splicing machinery?
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Using a site in Northern California, you repeat Stiling and Drake's experiments in elevated and ambient CO2 chambers, and achieve similar results. However, you notice that for one species of herbivore, the mortality rate from predators and parasitoids is equal in the elevated and ambient chambers, while the mortality rate due to nutritional inadequacy is higher in elevated chambers. The herbivore species in question is native to Asia and has only recently arrived in the United States. What is a likely explanation for your findings?
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