Given that the enzymes that catalyze nitrogen fixation are inhibited by oxygen, what are two ʺstrategiesʺ that nitrogen-fixing prokaryotes might use to protect these enzymes from oxygen?

1.  couple them with photosystem II (the photosystem that splits water molecules)

2.  package them in membranes that are impermeable to all gases

3.  be obligate anaerobes

4.  be strict aerobes

5.  package these enzymes in specialized cells or compartments that inhibit oxygen entry

#Question id: 4311

#Unit 3. Fundamental Processes

At the beginning of this century, there was a general announcement regarding the sequencing of the human genome and the genomes of many other multicellular eukaryotes. Many people were surprised that the number of protein-coding sequences was much smaller than they had expected. Which of the following types of DNA make up the rest of the human genome?

#Question id: 4312

#Unit 3. Fundamental Processes

Among the newly discovered small noncoding RNAs, one type helps to reestablish ethylation patterns during gamete formation and blocks expression of some transposons. Which of the following types of RNA is responsible for this function?

#Question id: 4313

#Unit 3. Fundamental Processes

Which of the following statements best describes the characteristics of siRNA?

#Question id: 4314

#Unit 3. Fundamental Processes

A researcher introduces double-stranded RNA into a culture of mammalian cells and can identify its location or that of its smaller subsections experimentally, using a fluorescent probe. Some time later, she finds that the introduced strand separates into single-stranded RNAs, one of which is degraded. What does this enable the remaining strand to do?

#Question id: 4315

#Unit 3. Fundamental Processes

A researcher introduces double-stranded RNA into a culture of mammalian cells and can identify its location or that of its smaller subsections experimentally, using a fluorescent probe. When she finds that the introduced strand separates into single-stranded RNAs, what other evidence of this single-stranded RNA piece's activity would she find?

#Question id: 4316

#Unit 3. Fundamental Processes

Which of the following processes do normal proto-oncogenes typically exhibit?