Cellular Communication

• Cellular Communication involves a 60-question multiple-choice test

Cell Signal Transduction

• Reception is the first step
• Desensitization is a characteristic
• A ligand is a molecule that binds to a receptor
• Endocrine signals target distant cells via the bloodstream

Cell Signaling Receptors

• Cell signaling receptors can be located on the cell surface and intracellularly
• Intracellular receptors are NOT a type of cell-surface receptor
• Ionotropic receptors are ligand-gated ion channels, this is a key difference between ionotropic and metabotropic receptors

Second Messengers

• cAMP is a second messenger
• Second messengers are primarily hydrophobic, hydrophilic and gases
• Second messengers spread the signal to other parts of the cell

GPCRs

• G-protein coupled receptors (GPCRs) have a general structure of seven transmembrane helical segments
• Approximately 35% of marketed drugs target GPCRs
• GTP exchanges with GDP to activate the G protein in G protein activation
• The GTPase enzyme hydrolyzes GTP to GDP
• The cAMP pathway is a GPCR-mediated pathway

cAMP

• Adenylyl cyclase synthesizes cAMP
• cAMP activates protein kinase A

Enzymes

• Protein kinase, an intracellular enzyme, is activated by second messengers and can phosphorylate other proteins
• Phosphorylation is the process of adding a phosphate group to a protein

Hormone/Enzyme Cascade

• A hormone/enzyme cascade amplifies the signal

Signal Termination

• GTP hydrolysis is an example of signal termination
• GTPase-activator proteins (GAPs) speed up GTP hydrolysis, they inhibit G proteins
• Signal desensitization is a decrease in cellular response to a signal
• Signal desensitization can be reversed only in certain cell types

CREBs

• CREBs are transcription factors
• Protein kinase A activates CREBs
• CREBs regulate gene expression

GPCR Phosphatidylinositol PIP2 Pathway

• DAG is involved in the GPCR phosphatidylinositol PIP2 pathway

Calcium

• Calcium acts as a second messenger in cell signaling
• Cells maintain low intracellular Ca2+ concentrations by using Ca2+ pumps
• Calmodulin is the protein that binds to calcium to mediate its intracellular effects
• Calmodulin regulates calcium-dependent enzymes

Receptor Protein Kinases

• Receptor protein kinases differ from GPCRs in that they have intrinsic kinase activity

Gated Ion Channels

• Gated ion channels are membrane proteins that open to allow ions to pass
• Gated ion channels are found on the plasma membrane
• Ligand binding activates gated ion channels

Receptor-Mediated Endocytosis

• Receptor-mediated endocytosis is relevant for internalizing receptors and their bound ligands

Intracellular Receptors

• Intracellular receptors bind to hydrophobic ligands
• Activation of intracellular receptors triggers alterations in gene expression

Kinases

• Kinases are enzymes that catalyze phosphorylation of proteins

Receptor Tyrosine Kinases RTKs

• Receptor tyrosine kinases (RTKs) are activated by autophosphorylation
• Insulin is an example of a ligand for Receptor Tyrosine Kinase

Ionotropic Receptors

• Ionotropic receptors are also known as ligand-gated ion channels
• Sodium (Na+), Potassium (K+) and Chloride (Cl-) are commonly associated with ionotropic receptors

Lipophilic Ligands

• Steroid hormones are an example of a lipophilic ligand that binds to intracellular receptors

Cellular Response

• Ligand-gated ion channels leads to the fastest cellular response

Clathrin

• Clathrin is essential for receptor mediated endocytosis

cAMP Pathway

• In the cAMP pathway, G protein activates adenylyl cyclase

Intracellular Signaling

• Diacylglycerol (DAG) is a hydrophobic second messenger
• Inositol trisphosphate (IP3) primarily functions to release calcium from intracellular stores

Signal Molecule Desensitization

• Receptor upregulation is NOT a mechanism by which target cells can become desensitized to a signal molecule

Beta-Adrenergic Receptors

• Beta-adrenergic receptors are examples of G protein-coupled receptors

Enzymes

• The alpha subunit of a G protein activates adenylyl cyclase in the cAMP pathway
• cAMP activates Protein kinase A
• The second messenger diacylglycerol (DAG) activates protein kinase C

G Proteins

• G proteins are heterotrimeric proteins consisting of α, β, and γ subunits

GPCR Pathway Termination

• Termination of the GPCR pathway can involve intrinsic GTPase activity of the G protein

Beta-Blocker Drugs

• Beta-blocker drugs are used to treat Tachyarrhythmias/high blood pressure

Agonists

• Agonists are molecules that bind to a receptor and mimic the effects of its natural ligand