Topic 6: Chemical Signals

What are the two main types of signals in cell signaling?

Electrical signals in the nervous system and chemical signals (hormones, paracrines, autocrines, pheromones) in the endocrine system.

What is the role of second messengers in cell signaling?

They amplify and transmit signals within cells, regulating cellular function and homeostasis.

What initiates the Phospholipase C pathway?

Specific G proteins activate Phospholipase C (PLC), which cleaves phosphoinositol bisphosphate (PIP2) from the cell membrane.

What are the two second messengers produced by the Phospholipase C pathway?

Inositol triphosphate (IP3) and Diacylglycerol (DAG).

How does Inositol triphosphate (IP3) function in the cell?

It acts on the smooth endoplasmic reticulum to open calcium channels, releasing calcium ions into the cytoplasm.

What is the role of Diacylglycerol (DAG) in cell signaling?

It activates protein kinase C (PKC), which phosphorylates various proteins, including calcium channels.

What is calcium's role as a second messenger?

Calcium (Ca²⁺) affects the electrical charge inside the cell and is critical for contraction and neurotransmitter secretion.

What does calmodulin do in the signaling pathway?

Calmodulin binds to calcium and activates calmodulin-dependent protein kinase, which phosphorylates proteins for various cellular effects.

What is the function of cAMP-dependent protein kinase?

It is activated by cyclic AMP (cAMP) generated from ATP by adenylate cyclase, playing a role in signal transduction.

What are the key differences between the Nervous System (NS) and Endocrine System (ES)?

NS uses electrical signals, is fast, and has high specificity; ES uses chemical signals, is slow, and has low specificity.

What is the primary function of the Nervous System?

To regulate overall activity and respond to sudden stimuli, such as reflexes and sensory input.

What is the primary function of the Endocrine System?

To regulate slower processes like digestion, growth, and stress responses.

What is the significance of homeostatic reflex arcs in NS and ES?

Both systems act as integrating centers, receiving sensory input and sending signals to effectors.

What are the common principles of signal transduction shared by NS and ES?

Both require a stimulus, involve electrical signals, and utilize specific receptors for chemical signals.

What is the difference in the gap between control cells and target cells in NS and ES?

NS has a tiny gap (synaptic cleft), while ES has a large gap (entire bloodstream).

What type of signal does the Nervous System secrete?

Neurotransmitters across the synaptic cleft.

What type of signal does the Endocrine System secrete?

Hormones into the bloodstream.

How does the specificity of the Endocrine System work?

Only cells with the correct receptor will respond to hormones, despite their widespread distribution.

What are the types of chemical signaling in the body?

Neural, paracrine, autocrine, endocrine, neurohormonal, and pheromonal signaling.

What is paracrine signaling?

Cell secretes chemicals into interstitial fluid to affect nearby neighboring cells.

What is autocrine signaling?

Cell secretes a chemical that acts back on its own receptors, providing self-control.

What are neurohormones?

Chemicals secreted by neurons into the bloodstream, acting like hormones.

What is the 'Prison/Dorm Effect' in human pheromones?

Synchronization of menstrual cycles in females living in close proximity.

What is the significance of pheromonal signaling in humans?

It involves chemical signals released to affect other individuals, such as in parental bonding and mate attraction.

What are shared chemical signals in the body?

Chemicals used by both endocrine and nervous systems, such as adrenaline (hormone) and epinephrine (neurotransmitter), which affect target organs like the heart.

What is a first messenger in signal transduction?

Chemicals released from regulatory cells that travel to target cells, examples include neurotransmitters, hormones, paracrines, autocrines, and pheromones.

What is a second messenger?

Intracellular molecules that relay and amplify signals from first messengers, working inside cells to continue the signal pathway.

Describe the function of gated ion channels in signal transduction.

A receptor protein complex that opens or closes in response to a first messenger, allowing ions to flow through and change the membrane potential.

What is the cAMP/Protein Kinase (PK) pathway?

A pathway where a first messenger activates G proteins, which interact with adenylate cyclase to convert ATP to cyclic AMP (cAMP), leading to protein phosphorylation and cellular responses.

How does signal amplification occur in the cAMP pathway?

One first messenger molecule can lead to the production of many cAMP molecules, each activating multiple protein kinases, resulting in a massive cellular response.

What role do Gs and Gi G-proteins play in the cAMP pathway?

Gs stimulates adenylate cyclase while Gi inhibits it, allowing for fine control of the pathway's activity.

What is the IP3 and DAG pathway?

A pathway involving Phospholipase C that cleaves PIP2 into IP3 and DAG, where IP3 releases Ca²⁺ from the endoplasmic reticulum and DAG activates protein kinase C (PKC).

Explain the Calcium & Calmodulin pathway.

Cytoplasmic Ca²⁺ binds to calmodulin, activating it, which then activates calmodulin-dependent protein kinase, leading to protein phosphorylation.

What is the role of Nitric Oxide (NO) in signal transduction?

NO is a gas that diffuses across cell membranes, activating guanylate cyclase to produce cyclic GMP (cGMP), which causes smooth muscle relaxation.

How does Viagra relate to the Nitric Oxide pathway?

Viagra promotes smooth muscle relaxation in penile blood vessels by enhancing the effects of NO and cGMP, originally developed for heart-related conditions.

What are receptor-linked kinases?

Receptors with intrinsic enzyme activity (like tyrosine kinase) that phosphorylate proteins upon activation by a first messenger.

What is the function of Janus Kinase (JAK) in signaling?

JAK is a kinase that is activated by receptor activation and phosphorylates proteins to elicit a cellular response.

Describe the Eicosanoids pathway.

Involves Phospholipase A cleaving phospholipids to produce arachidonic acid, which can enter pathways leading to prostaglandins or leukotrienes.

What are the roles of prostaglandins and leukotrienes?

Prostaglandins are associated with inflammation and blood vessel changes, while leukotrienes typically reduce inflammation.

How does aspirin affect the Eicosanoids pathway?

Aspirin inhibits the cyclooxygenase pathway, reducing the production of prostaglandins involved in inflammation.

What is the gene expression pathway for steroid and thyroid hormones?

These hormones diffuse across cell membranes, bind to intracellular receptors, and act as transcription factors to regulate gene expression.

What is the timing and duration of effects from steroid hormones?

They have delayed effects due to the time required for gene transcription and protein synthesis, but their effects last longer as newly synthesized proteins persist.

How do rescue inhalers differ from maintenance inhalers in asthma treatment?

Rescue inhalers provide immediate relief through second messenger activation, while maintenance inhalers work on gene expression for long-term control.