Professor Marcus is studying gene expression in the liver cells of a mouse. She observes that when a steroid hormone enters the liver cells, the cells begin producing a wide variety of new proteins. Which of the following statements is the MOST USEFUL to include in an explanation of this observation? A. The steroid hormone contains several genes. B. A transcription factor activates a single gene that produces several proteins. C. A transcription factor activates many genes at the same time. D. The steroid hormone mimics the function of several mRNA molecules.

Choose the incorrect statement (a) the motor end plate membrane is only capable of generating graded potentials, but it is contiguous with the skeletal muscle sarcolemma, which can generate action potentials. (b) propagation of an action potential through the t-tubules into the sarcoplasmic reticulum triggers the release of ca++ into the cytoplasm of a skeletal muscle fiber. (c) the generation of suprathreshold endplate potentials in multiple muscle fibers could be due to the increased frequency of action potential generation at the axon hillock of a single motor neuron. (d) a greater amount of ach would be found in the presynaptic vesicles of a motor unit that fired several action potentials after exposure to botulinum toxin, than in a motor unit that fired several action potentials after exposure to the venom of the krait snake (which contains α-bungarotoxin).