What is the role of cis-acting and trans-acting factors in transcription? Explain how these factors play a role in the lac operon, and discuss how complementation can be used to identify where the mutations have occurred (structural genes versus
regulatory regions). Which type of mutations can be complemented by a second gene with normal function? Are IS and OC mutants cis- or trans-acting?
If a factor is trans-acting, genes that are not physically adjacent can be regulated together and are mediated by genes that encode regulatory proteins. The lac repressor is an example of a trans-acting element because mutations can be complemented by a second gene with normal function.
If a factor is cis-acting, the DNA sequence must be adjacent to the genes it regulates. The lac operator is an example of a cis-acting element because mutations cannot be complemented by a second normal element.
Trans-acting factors (and complementation) indicate mutations in structural genes, whereas
cis-acting factors indicate regulatory sequences have been mutated.
IS is a trans-acting mutation because the mutation disrupts ligand binding of the repressor to the operator on both copies of the DNA. OC is a cis-acting mutation because only one molecule of DNA is unable to be repressed due to the mutation. The operon is constitutively active on the molecule of DNA that contains the OC allele, but the other copy of the gene is intact and functions properly when the repressor is present.
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A. habitat loss B. overexploitation C. introduced species D. pollution E. climate change Clarify Question · What is the key concept addressed by the question? · What type of thinking is required? Gather Content · What do you already know about causes of extinction? 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?
Vertebrate locomotion results from the contraction of muscles anchored to what other tissue?
A. bone B. an exoskeleton C. each other D. nerves E. the plasma membrane
Discrete packets of kinetic energy in light are called
A. lasers. B. grana. C. photons. D. protons. E. electrons.
Human males produce
A. sperm; half contain an X chromosome; half contain a Y chromosome. B. sperm with neither an X nor a Y; gametes do not contain sex chromosomes. C. gametes; all contain a Y chromosome. D. gametes; all contain both an X chromosome and a Y chromosome. E. sperm; all contain an X chromosome.