Words to know 2_2025

Overview of Signaling

• Cell Surface Receptors: Proteins on the cell membrane that detect external signals.

• Intracellular Receptors: Receptors located inside the cell that respond to lipophilic molecules.

• Hydrophilic Signal Molecules: Molecules that cannot cross the cell membrane and bind to external receptors.

• Hydrophobic Signal Molecules: Molecules that can cross the cell membrane to bind with intracellular receptors.

Key Concepts in Signaling

• Affinity: The strength of the interaction between a ligand and its receptor.

• Amplification: The process where one signal leads to a greater response within the cell.

• Adaptation: The process by which cells become less responsive to persistent signals.

Types of Molecules

• Steroid Hormones: Include testosterone, estrogen, progesterone, corticosteroids, thyroid hormones, which bind to intracellular receptors.

• Ligand: A molecule that binds to a receptor and elicits a response.

• Second Messengers: Small molecules that propagate a signal within the cell (e.g., cAMP, cGMP).

  • cAMP (cyclic adenosine monophosphate): Acts as a second messenger in many signaling pathways.

  • cGMP (cyclic guanosine monophosphate): Another second messenger often involved in vasodilation.

  • PIP2 (Phosphatidylinositol 4,5-bisphosphate): A precursor for two second messengers: IP3 and diacylglycerol.

  • Diacylglycerol: Acts as a second messenger in the activation of protein kinase C (PKC).

Signaling Pathways

• Effector Proteins: Proteins that enact the response dictated by receptor activation.

• Paracrine Signaling: Communication between neighboring cells.

• Endocrine Signaling: Hormonal signals that travel through the bloodstream to distant sites.

Receptor Types

• Ion-Channel Coupled Receptors: Open to let ions in or out of the cell in response to neurotransmitters (e.g., acetylcholine receptors).

• GPCR (G protein-coupled receptors): Largest family of receptors, activate G proteins upon binding of a ligand.

  • Composed of alpha, beta, and gamma subunits.

• Receptor Tyrosine Kinases (RTKs): Mediate cellular responses to growth factors and hormones.

Feedback Mechanisms

• Positive Feedback: Enhances or accelerates an outcome.

• Negative Feedback: Reduces the output or activity of a system.

• Feedback Loop: System's response feeds back into the system to influence the process.

Classical Signaling Pathways Details

• Testosterone, Estrogen, Progesterone, Corticosteroids, Thyroid Hormones: Involves binding to nuclear receptors, affecting gene expression.

• Inhibitory Proteins: Regulate signaling pathways, can interfere with receptor action.

• G Proteins: Relay signals from receptors to effector proteins; types include Gs (stimulatory) and Gi (inhibitory).

Important Participants in Signaling

• Adenylyl Cyclase and Guanylyl Cyclase: Enzymes that produce cAMP and cGMP, respectively.

• Cholera Toxin: Modifies Gs protein, leading to increased cAMP levels and diarrhea.

• PKA (Protein Kinase A): Activated by cAMP; phosphorylates target proteins.

• CREB (cAMP response element-binding protein): Transcription factor activated by PKA.

Cell Death Mechanisms

• Necrosis: Uncontrolled cell death due to damage.

• Apoptosis: Programmed cell death, involves caspases (e.g., initiator caspases 8 and 9, executioner caspases 3, 6, and 7).

  • Related to pathways: intrinsic (mitochondrial) and extrinsic (death receptor mediated).

Nucleocytoplasmic Transport

• Mechanically Gated Channels: Open in response to mechanical stress.

• Nuclear Pore Complex: Regulates transport between the nucleus and cytoplasm.

• Karyopherin: Mediates transport of proteins containing nuclear localization signals (NLS) into the nucleus.

Chromatin and Genome Organization

• Nuclear Structure: Includes the nuclear membrane, nuclear lamina, and chromatin organization.

• Nucleosome: Fundamental unit of chromatin structure, composed of histone proteins and DNA.

• Euchromatin vs. Heterochromatin: euchromatin is less dense and more transcriptionally active than heterochromatin.