3.4.5Inquiry Process
Epinephrine Receptors — IB Biology HL Revision Notes & Topical Questions
5 min read 5 parts Lesson 130 of 160
Curriculum Equation Key قوانين الرقم الهيدروجيني والاتزان الأيوني - pH & Acid-Base Equilibrium FormulasFast Exam Solution
pH = -log[H⁺] | pOH = -log[OH⁻] | pH + pOH = 14 | [H⁺][OH⁻] = 10⁻¹⁴
Word Equation & Conditions: الرقم الهيدروجيني = -لوغاريتم تركيز أيون الهيدروجين | pH + pOH = 14
Location & Specifications: الاتزان الأيوني، كيمياء 3 ثانوي، التحصيلي، و AP Chemistry.
Part 1 of 5Epinephrine and Its Receptor
Epinephrine
- Epinephrine Also called adrenaline, this hydrophilic hormone is released from the adrenal glands in stress and prepares the body for vigorous activity.
Receptor type
- Receptor type Its receptor is a G-protein-linked transmembrane protein, so the hormone binds outside the cell and never enters.
Target cells
- Target cells Cells in the liver, heart and skeletal muscle carry epinephrine receptors, but each tissue responds in its own way.
Speed
- Speed Because existing enzymes are activated rather than new proteins made, the body responds within seconds of the hormone arriving.
Part 2 of 5The Signalling Pathway
1
Epinephrine binds the receptor, which changes shape on the inner side of the membrane.
2
The receptor activates a G protein, which exchanges GDP for GTP and then switches on adenylyl cyclase.
3
Adenylyl cyclase converts ATP into cyclic AMP, the second messenger, which spreads through the cytoplasm.
4
Cyclic AMP activates protein kinase A, which phosphorylates and so activates further enzymes in a cascade.
5
In a liver cell the cascade activates glycogen phosphorylase, breaking glycogen down so glucose can be released into the blood.
Part 3 of 5Effects and Amplification
Effects and Amplification
Liver
- Liver Glycogen breakdown raises blood glucose, supplying fuel to muscles that must work hard in a stress response.
Heart
- Heart Cells contract faster and more strongly, so cardiac output rises and blood reaches the muscles more quickly.
Amplification
- Amplification One hormone molecule leads to many cyclic AMP molecules, each activating enzymes that act on many substrates,
- so the response is greatly magnified.
Termination
- Termination The effect ends when epinephrine is removed and cyclic AMP is broken down, halting the cascade.
| Step | Molecule involved | Result |
|---|---|---|
| 1 | Epinephrine and receptor | Receptor changes shape |
| 2 | G protein | Activates adenylyl cyclase |
| 3 | Cyclic AMP | Second messenger produced |
| 4 | Protein kinase A | Enzyme cascade starts |
Part 4 of 5Worked Example
Question
- Suppose each receptor-activated adenylyl cyclase makes 100 cyclic AMP molecules, and each cyclic AMP activates one protein kinase which activates 10 enzyme molecules.
- How many enzyme molecules are activated per active adenylyl cyclase?
- One adenylyl cyclase makes 100 cyclic AMP molecules.
- 100 cyclic AMP activate 100 protein kinases (one each).
- Each kinase activates 10 enzymes, so 100 × 10 = 1000.
Answer About 1000 enzyme molecules per active adenylyl cyclase, showing how the cascade amplifies the signal.
Part 5 of 5Exam Checklist & Tips
3.4.5 – Key Points for the Exam
- Epinephrine A hydrophilic hormone from the adrenal gland that prepares the body for action.
- Cyclic AMP A second messenger made from ATP by adenylyl cyclase inside the cell.
- Protein kinase An enzyme that adds phosphate groups to other proteins, changing their activity.
- Glycogen phosphorylase Liver enzyme activated in the cascade that breaks glycogen down to glucose phosphate.
Common Mistakes
- Saying epinephrine enters the cell; it binds a surface receptor.
- Writing that cyclic AMP is the first messenger; it is the second messenger.
- Forgetting amplificationa few hormone molecules produce a large response.
- Mixing glycogen breakdown with glycogen synthesis, which insulin promotes.
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