Test Ch16 Flashcards
Signal Transduction
Cell receives signal from environment, which must be
transmitted into cell for response.
In order to react to a signal a cell must be able to:
- Recognize the signal = have a specific receptor
- Transfer the signal across the membrane
- Transmit the signal to specific intracellular molecules to
trigger response
- Turn off the signal
Signaling
Four ways cells signal
- endocrine
- Paracrine
- Neuronal
- Contact-dependent
- endocrine signaling
- Paracrine signaling
- Neuronal Signaling
- Contact Dependent Signaling (Juxtacrine)
Cellular responses to signals (fast and slow)
Fast Response (Seconds to Minutes):
This occurs when the signal leads to an altered protein function.
Existing proteins in the cell are modified, leading to immediate effects without the need for new protein synthesis.
Example: Activation of enzymes in a signaling pathway.
Slow Response (Minutes to Hours):
This involves changes in gene expression, requiring transcription (DNA to RNA) and translation (RNA to protein).
The signal triggers new protein synthesis, which takes longer to produce an effect.
Example: Hormones that regulate gene expression, like steroid hormones.
Key takeaway: Both fast and slow responses ultimately alter cellular machinery and behavior.
How different cells respond to the same signal
The slide illustrates how the same signal (acetylcholine, a neurotransmitter) can produce different effects depending on the receptor and target cell:
Heart pacemaker cell (Muscarinic Ach receptor) → Decreased heart rate
Salivary gland cell (Muscarinic Ach receptor) → Secretion of saliva
Skeletal muscle cell (Nicotinic Ach receptor) → Contraction
Why does the response differ?
Different cell types have different receptors for acetylcholine.
Muscarinic receptors (heart & salivary gland) work via G-protein coupled pathways, leading to inhibition or secretion.
Nicotinic receptors (skeletal muscle) are ligand-gated ion channels, causing muscle contraction.
Key takeaway: The same signaling molecule can trigger different cellular responses depending on the receptor type and cell function.
Cytoplasmic vs. cell surface receptors
Intracellular receptor: Steroid hormones
Steroid hormones, like cortisol, bind to intracellular receptors (inside the cell) instead of surface receptors, leading to slow but long-lasting effects by altering gene expression.
Key Takeaways:
Steroid hormones are hydrophobic, allowing them to pass through the plasma membrane.
They bind to intracellular receptors, which then act as transcription factors in the nucleus.
This process leads to gene transcription (RNA synthesis), resulting in slow but sustained cellular changes.
Intracellular receptor: Nitric oxide
The slide explains how nitric oxide (NO) is produced by endothelial cells in response to acetylcholine. NO rapidly diffuses across membranes and binds to guanylyl cyclase in smooth muscle cells, leading to the production of cyclic GMP (cGMP). This triggers smooth muscle relaxation, which helps blood vessels dilate, improving blood flow. The slide also notes that NO acts in a paracrine manner (affecting nearby cells) and is used in heart medications like Viagra.
Location of Receptors
Small, hydrophobic molecules that diffuse freely through membrane
have intracellular receptors ex:
Steroids (cholesterol derivatives)
Dissolved gas
Large, charged, polar molecules require cell surface receptors
3 classes of cell surface receptors
- Ion-channel-coupled receptors
- G-protein-coupled receptors
- Enzyme-coupled receptors
Ion-channel-coupled receptors
All other cell surface receptors cause signaling cascade
G-protein-coupled receptors (GPCRs) – These receptors activate G proteins, which then activate enzymes that trigger intracellular signaling.
Enzyme-coupled receptors – These receptors become active when signal molecules bind, leading to enzyme activation inside the cell.
The handwritten note emphasizes that a signaling cascade is a series of molecules that interpret and pass on signals throughout the cell, leading to cellular responses.
G-protein coupled receptors (GPCR) are largest family of cell surface receptors
Primary Transduction – A signal molecule binds to a receptor on the plasma membrane.
Relay – The signal is passed along through intracellular molecules.
Transduce and Amplify – The signal is amplified, meaning one signal can lead to multiple responses.
Integrate, Feedback, and Distribute – The signal is processed, regulated, and spread to different cellular targets, leading to changes in metabolism, movement, or gene expression.
The handwritten note highlights that one signal can trigger many responses and that each step of the cascade must have an “off” mechanism to stop signaling when needed.
These slides emphasize how extracellular signals cause intracellular changes through a regulated chain reaction.
