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Review Question - QID 218807

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QID 218807 (Type "218807" in App Search)
A scientist is studying the behavior of a novel hormone receptor in humans. The hormone is found to circulate systemically in the bloodstream and results in pleomorphic effects in different organ systems. She isolates cells that express the hormone receptor and uses differential centrifugation techniques in order to fractionate the membranes present in the cell. She finds that the hormone receptor is expressed in both the cytosolic and nuclear fractions of the homogenate but is not present on the plasma membrane or low-density membrane fractions of the homogenate. She uses formaldehyde to crosslink the receptor in the nuclear fraction of the homogenate and found that the receptor is bound to DNA. Which of the following hormones would most likely bind to the receptor described in this case?

Cortisol

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Glucagon

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Insulin

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Nitric oxide

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Prolactin

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This receptor that exists in the cytoplasm and is bound to DNA in the nucleus can be a steroid hormone receptor, a lipophilic vitamin receptor, or a lipophilic hormone receptor. Cortisol and other glucocorticoids are examples of hormones that use a steroid receptor.

DNA binding proteins are specialized to have a segment that binds to specific sequences of nucleic acid through complementary hydrogen bonding interactions. These proteins also have an active domain that has diverse functions depending on the type of DNA-binding protein being identified. Examples include transcription factors, steroid receptors, thyroid hormone receptors, and fat-soluble vitamin receptors. Of note, all DNA binding proteins must have a mechanism for being imported into the nucleus where they can interact with substrate sequences. Hybrid proteins with a DNA binding domain of one protein and a modified active domain are often used in research to modulate transcriptional activity.

Etzion-Fuchs et al. created a method of predicting which protein domains would bind to DNA. They found that this technique allows for predictions of where proteins bind for 95% of ligand-binding proteins. They recommend using this tool in order to better understand human protein binding effects.

Incorrect Answers:
Answer 2: Glucagon uses a G-protein coupled receptor pathway. These receptors are located on the plasma membrane and activate cytosolic second messengers such as cyclic adenosine monophosphate in order to achieve target effects.

Answer 3: Insulin uses a tyrosine kinase receptor pathway. These receptors are located on the cell surface and transphosphorylate adjacent insulin receptors in order to provide a binding domain for downstream signaling second messengers.

Answer 4: Nitric oxide diffuses into the cytosol through the plasma membrane and activates guanylyl cyclase activity. These receptors remain within the cytosol and produce cyclic guanine monophosphate in order to achieve target effects.

Answer 5: Prolactin uses a Janus kinase and signal transducer and activator of transcription (JAK/STAT) signaling pathway. These receptors are located on the plasma membrane and cause the phosphorylation of STAT proteins that subsequently diffuse into the nucleus.

Bullet Summary:
DNA binding proteins include transcription factors, steroid receptors, thyroid hormone receptors, and fat-soluble vitamin receptors.

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