Multiple Choice
The transcription of new messenger RNA is a function of __________.
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16. The Endocrine System
Membrane Bound Receptors and Secondary Messengers
Problem 22
Textbook Question
A researcher observes that stimulation by a particular hormone induces a marked increase in the activity of G proteins in the target plasma membrane. The hormone being studied is probably:
(a) A steroid
(b) A peptide
(c) Testosterone
(d) Estrogen
(e) Aldosterone
Verified step by step guidance1
Step 1: Understand the role of G proteins in cell signaling. G proteins are intracellular proteins that act as molecular switches inside cells, and they are typically activated by cell surface receptors known as G protein-coupled receptors (GPCRs). These receptors respond to extracellular signals like hormones by activating G proteins.
Step 2: Identify which types of hormones commonly use G protein-coupled receptors for their signaling. Peptide hormones often bind to GPCRs on the plasma membrane, leading to activation of G proteins and subsequent intracellular signaling cascades.
Step 3: Recognize that steroid hormones (such as testosterone, estrogen, and aldosterone) generally do not activate G proteins directly. Instead, they typically diffuse through the plasma membrane and bind to intracellular receptors that act as transcription factors to regulate gene expression.
Step 4: Compare the hormone options given: (a) steroid hormones (testosterone, estrogen, aldosterone) versus (b) peptide hormones. Since the question states that the hormone induces increased G protein activity at the plasma membrane, the hormone is more likely to be a peptide hormone.
Step 5: Conclude that the hormone stimulating G protein activity is probably a peptide hormone, as peptide hormones commonly use GPCRs and G proteins for signal transduction.
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Key Concepts
Here are the essential concepts you must grasp in order to answer the question correctly.
G Protein-Coupled Receptors (GPCRs)
GPCRs are membrane receptors that activate G proteins upon binding to specific ligands like hormones. This activation triggers intracellular signaling cascades. Hormones that act through GPCRs typically include peptides and some amines, leading to rapid cellular responses.
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G Protein-Coupled Receptors
Steroid Hormone Signaling
Steroid hormones, such as testosterone, estrogen, and aldosterone, usually pass through the plasma membrane and bind to intracellular receptors. Their signaling does not typically involve G proteins but rather direct regulation of gene transcription in the nucleus.
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5:13Actions of Steroid Hormones
Hormone Types and Their Mechanisms
Hormones are classified by their chemical nature: peptides (water-soluble) often bind to surface receptors activating G proteins, while steroids (lipid-soluble) enter cells to modulate gene expression. Understanding these differences helps identify which hormone likely activates G proteins.
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