What is most likely to happen to an animal's target cells that lack receptors for local regulators?
A) They might compensate by receiving nutrients via a factor. B) They could develop normally in response to neurotransmitters instead. C) They could divide but never reach full size. D) They might not be able to multiply in response to growth factors from nearby cells. E) Hormones would not be able to interact with target cells.
Which of the following is characterized by a cell releasing a signal molecule into the environment, followed by a number of cells in the immediate vicinity responding?
A) hormonal signaling B) autocrine signaling C) paracrine signaling D) endocrine signaling E) synaptic signaling
Of the following, a receptor protein in a membrane that recognizes a chemical signal is most similar to
A) the active site of an allosteric enzyme that binds to a specific substrate. B) tRNA specifying which amino acids are in a polypeptide. C) a metabolic pathway operating within a specific organelle. D) an enzyme having an optimum pH and temperature for activity. E) an antibody in the immune system.
Which of the following is true for the signaling system in an animal cell that lacks the ability to produce GTP?
A) It would not be able to activate and inactivate the G protein on the cytoplasmic side of the plasma membrane. B) It could activate only the epinephrine system. C) It would be able to carry out reception and transduction but would not be able to respond to a signal. D) It would use ATP instead of GTP to activate and inactivate the G protein on the cytoplasmic side of the plasma membrane. E) It would employ a transduction pathway directly from an external messenger.
One of the major categories of receptors in the plasma membrane reacts by forming dimers, adding phosphate groups, and then activating relay proteins. Which type does this?
A) G protein-coupled receptors B) ligand-gated ion channels C) steroid receptors D) receptor tyrosine kinases
Since steroid receptors are located intracellularly, which of the following is true?
A) The receptor molecules are themselves lipids or glycolipids. B) The steroid/receptor complex can cross the nuclear membrane. C) The unbound steroid receptors are quickly recycled by lysosomes. D) The concentration of steroid receptors must be relatively high in most cells. E) The receptor molecules are free to move in and out of most organelles.
Which of the following is the best explanation for the inability of a specific animal cell to reduce the Ca2+ concentration in its cytosol compared with the extracellular fluid?
A) blockage of the synaptic signal B) loss of transcription factors C) insufficient ATP levels in the cytoplasm D) low oxygen concentration around the cell E) low levels of protein kinase in the cell
What explains the increased concentration of Ca++ in the ER?
A) Calcium ions are actively imported from the cytoplasm into the ER. B) Calcium concentration is kept low in the cytoplasm because of its high usage level. C) Calcium cannot enter the plasma membrane through ion channels. D) Calcium levels in the blood or other body fluids are extremely low. E) The Ca ions are recycled from other molecules in the ER.
When a neuron responds to a particular neurotransmitter by opening gated ion channels, the neurotransmitter is serving as which part of the signal pathway?
A) receptor B) relay molecule C) transducer D) signal molecule E) endocrine molecule -
Adenylyl cyclase has the opposite effect of which of the following? A) protein kinase B) protein phosphatase C) phosphodiesterase D) phosphorylase E) GTPase