1 A) Blocking transcription by interfering with RNA polymerase binding. B) Stimulation of transcription by facilitating RNA polymerase binding to a promoter. C) Hormonal alteration of gene expression. D) Homeostasis of metabolic reactions. E) Apoptosis of a eukaryotic cell. 2 A) The C-G pair would have more hydrogen bond acceptors on the right than on the left. B) The C-G pair would have a partially positive charge to the left, and two electronegative (partially negative charged) groups to its right. C) It can't happen because purines are all found on one strand, while the other DNA strand is composed of pyrimidines. D) Ionic bonds rather than hydrogen bonds would hold the nucleotides together. E) There would be no difference for either orientation. 3 A) Binding of the lac repressor to the operator of the lac operon. B) Binding of the trp repressor to the operator of the trp operon. C) Binding of the CAP-cAMP complex near the promoter of the lac operon. D) Both a and b are examples of positive regulation. E) None of the above is an example of positive regulation. 4 A) They modify the structure of RNA polymerase, which is free to diffuse in the direction of the gene which will be activated. B) They collect activator proteins which promote transcription, then are able to contact the initiation complex (to which RNA polymerase II is bound), stimulating transcription. C) Enhancers are proteins which stimulate transcription, and can move throughout the nucleoplasm. D) Regions of DNA far distant from an actual gene are catalytic, and can create end-products which activate RNA polymerase II. These end-products accumulate until there is sufficient activation for transcription to occur. 5 A) Transcription factors and RNA polymerase II cannot identify and bind the promoter. B) They promote methylation of certain bases in DNA which causes the gene to "turn off". C) They eliminate denaturation of DNA, which is required to generate template strands for transcription. D) Nucleosomes move the promoter so that it no longer is next to the coding sequence of the gene. E) Transcription factors are absorbed by nucleosomes, rendering them nonfunctional. 6 A) The poly-A tail may be shortened, causing RNA-digesting enzymes to have a harder time binding and destroying the transcript. B) miRNA can bind the mRNA to promote ribosome binding. C) RISC takes up bits of siRNA, forming a complex which identifies specific mRNA molecules to which it can bind. D) Translation factors can bind near the mG-cap. E) All of the above increase translation of an mRNA. 7 A) It is used to restore the carboxyl ends of the constituent amino acids so they can be recycled. B) It becomes available to ubiquitin ligase to mark another protein for destruction. C) The ubiquitin is phosphorylated to restore energy to the proteasome. D) Ubiquitin helps amino acids bind to aminoacyl tRNA synthetase in order to boost cellular levels of the various charged tRNA molecules.
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