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How cells communicate through chemical signals and receptors
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How cells communicate and respond to their environment
Three stages:
Receptors: Proteins that bind signal molecules (ligands)
Types:
Transduction: Converting signal into cellular response
Key mechanisms:
Small molecules that relay signals inside cell:
cAMP (cyclic AMP):
Ca²⁺ (calcium ions):
IP₃ and DAG:
Cellular responses:
Termination mechanisms:
Feedback mechanisms:
Describe the three stages of cell signaling: (a) reception, (b) transduction, and (c) response. Use the epinephrine (adrenaline) signaling pathway as a specific example, explaining signal amplification.
Cell Signaling - Three Stages:
(a) Reception:
Definition: Signal molecule binds to receptor protein
Epinephrine example:
Specificity:
(b) Transduction:
Definition: Signal converted to form that brings about cellular response
Epinephrine pathway (simplified):
Step 1: Epinephrine binds → receptor changes shape
Step 2: Activated receptor activates G protein
Step 3: G protein activates adenylyl cyclase (enzyme in membrane)
Step 4: Adenylyl cyclase converts ATP → cAMP (second messenger)
Step 5: cAMP activates protein kinase A (PKA)
Step 6: PKA activates phosphorylase kinase
Step 7: Phosphorylase kinase activates glycogen phosphorylase
(c) Response:
Definition: Transduced signal triggers specific cellular response
Epinephrine response:
Final enzyme: Glycogen phosphorylase
Cellular response:
Signal Amplification:
Cascade effect - each step amplifies signal:
1 epinephrine molecule
↓
~100 G proteins activated
↓
~1,000 adenylyl cyclase molecules activated
↓
~10,000 cAMP molecules produced
↓
~10,000 PKA activated
↓
~100,000 phosphorylase kinase activated
↓
~1,000,000 glycogen phosphorylase activated
↓
~100,000,000 glucose molecules released!
Amplification factor: ~10⁸-fold (100 million)!
Termination:
Why amplification matters:
Other examples:
| Section | Format | Questions | Time | Weight | Calculator |
|---|---|---|---|---|---|
| Multiple Choice | MCQ | 60 | 90 min | 50% | 🚫 |
| Free Response (Long) | FRQ | 2 | 50 min | 30% | 🚫 |
| Free Response (Short) | FRQ | 4 | 40 min | 20% | 🚫 |
Avoid these 3 frequent errors
See how this math is used in the real world