15 Questions
What is the primary method of hormone communication described in the text?
Interaction with extracellular receptors
How does an activated G protein affect adenylate cyclase?
It stimulates adenylate cyclase activity
Which molecule acts as the second messenger in the described signaling pathway?
cAMP
What happens to a G protein after its GTP is hydrolyzed?
It becomes inactive
What enzyme degrades cyclic AMP in the described pathway?
Phosphodiesterase
Which type of G protein stimulates adenylate cyclase in the pathway?
Gs protein
What enzyme is responsible for splitting the plasma membrane phospholipid PIP2 into DAG and IP3 in the PIP2-Calcium signaling mechanism?
Phospholipase C
Which of the following is NOT considered a second messenger in hormone signaling?
cAMP
In the PIP2-Calcium signaling mechanism, what is the function of the liberated Ca2+ ions?
Bind to calmodulin to activate enzymes
What is the term for the process where a hormone increases receptor number or affinity due to rising physiological levels?
Up-regulation
Which phenomenon refers to the decreased receptor number or affinity due to prolonged exposure to high hormone concentrations?
Down-regulation
In the context of hormone communication with target cells, what is the main function of G protein?
Activate adenylate cyclase
What does cyclic AMP stand for in the context of second messenger method of hormone communication?
Cyclic Adenosine Monophosphate
What is the name given to the U-shaped relationship wherein there are high risks at both extremes of exposure to substances like vitamin A?
Threshold effect
How does the second messenger method of hormone communication proceed following activation of adenylate cyclase?
Increase in cyclic AMP levels
Study Notes
Hormone Signaling
- Hormones bind to extracellular receptors, generating an intracellular molecule that mediates a response
- Second messengers are molecules that transmit signals from hormones within the cell
- There are different types of second messengers, including cyclic AMP (cAMP), cyclic GMP (cGMP), DAG, and IP3
cAMP Signaling Pathway
- When a hormone binds to its receptor, the receptor changes shape and activates a nearby inactive G protein
- The G protein, now active, moves along the plasma membrane and binds to adenylate cyclase
- Adenylate cyclase converts ATP to cyclic AMP (cAMP) with the help of a Gs protein
- cAMP activates protein kinase, an enzyme that adds a phosphate group to various proteins, amplifying the signal
- cAMP is degraded by the enzyme phosphodiesterase
Calcium Signaling Mechanism
- This pathway uses a G protein (Gq) and the enzyme phospholipase C
- Phospholipase C splits PIP2 into DAG and IP3
- DAG activates protein kinase, which triggers a response in the cell
- IP3 releases Ca2+ from intracellular storage sites, which bind to calmodulin
- The Ca2+-calmodulin complex activates enzymes that amplify the cellular response
Insulin Signaling Pathway
- Insulin binds to its receptor, activating its tyrosine kinase activity
- The activated insulin receptor serves as a docking site for intracellular relay proteins
- These proteins initiate a series of phosphorylations, triggering a cellular response
Regulation of Hormone Receptors
- Receptor numbers and affinity can change in response to hormone levels
- Up-regulation: increased receptor number or affinity due to rising hormone levels
- Down-regulation: decreased receptor number or affinity due to prolonged exposure to high hormone levels
Dose-Response Curve
- A graph showing the level of exposure (dose) and risk (increasing or decreasing) of an outcome
- Can be applied to substances other than hormones
- Threshold dose: the dose below which no effects are seen
- U-shaped relationship: high risks at both extremes of exposure
Hormone Communication Methods
- Two primary methods: second messenger and direct gene activation
- Second messenger method: hormone binds to receptor, activating a G protein, which generates a second messenger that triggers a response
- Direct gene activation method: hormone binds to receptor, which activates genes directly, without a second messenger
Test your knowledge on how second messenger hormones bind to extracellular receptors and mediate intracellular responses through G proteins. Learn about the activation process of G proteins and the role of second messengers in cellular signaling.
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