Some operons have both a positive and negative control mechanism built into the DNA sequence of the operon. That means both an activator protein and a repressor protein are present simultaneously. Consider a system that has both positive and repressible negative controls. a. Describe the four combinations of active or inactive regulatory proteins that could be present at any time in the cell.

(select all the correct choose each statement that is scientific. - the opinions of randomly selected participants in a survey prove the idea that global temperatures are not increasing on earth. - the universe's average temperature and rate of expansion support the idea that it began as one super-dense and hot mass 13.8 billion years ago. - ocean tides are caused by the uneven gravitational pulls of the moon and sun on different parts of earth. - human life is more valuable than other forms of life on earth because humans are more intelligent than other organisms.