Lecture 19 Review

G proteins are like cellular switches that help transmit signals inside cells.

G proteins activate enzymes in the cell membrane, which then produce small messenger molecules.

Two main targets of G protein-coupled receptors (GPCRs) are phospholipase C (PLC) and adenylyl cyclase.

Phospholipase C (PLC) produces certain lipids, while adenylyl cyclase generates cAMP.

cAMP activates Protein Kinase A (PKA), leading to a cascade of cellular responses.

cAMP plays a crucial role in various cellular processes, including increasing heart rate, glycogen breakdown, and fat breakdown.

IP3 acts as a second messenger by releasing Ca2+ from the endoplasmic reticulum, raising the cytosolic Ca2+ level.

Ca2+ acts as a second messenger and plays a role in various biological processes.

A process triggered by sperm-egg contact causing a rise in the egg's intracellular calcium levels. This wave-like increase in calcium is essential for preventing polyspermy and activating the egg for development.

Phospholipase C (PLC) is an enzyme activated by sperm-egg contact. It plays a role in breaking down PIP2 into IP3 and DAG, crucial signaling molecules for calcium release and subsequent egg activation.

IP3, a product of PIP2 breakdown by PLC, binds to receptors on the endoplasmic reticulum (ER) causing the release of calcium into the cytoplasm. This contributes to the overall increase in calcium levels essential for fertilization events.

Diacylglycerol (DAG), another product of PIP2 breakdown, works in conjunction with calcium to activate protein kinase C (PKC). This activation is crucial for triggering downstream signaling pathways involved in egg development.

Protein kinase C (PKC) is a crucial enzyme activated by DAG and calcium during fertilization. It initiates a cascade of phosphorylation events, leading to new protein synthesis and ultimately contributing to the egg's metabolic and developmental changes.

A category of cell-surface receptors that bind to ligands and directly function as enzymes. These enzymes often have catalytic activity within their cytoplasmic domains, initiating intracellular signaling cascades.

Receptor tyrosine kinases (RTKs) are a major class of enzyme-coupled receptors. They are activated by growth factors like FGF and EGF and their cytoplasmic domains function as tyrosine kinases, adding phosphate groups to tyrosine residues in proteins to regulate cellular processes.

Ras is a small GTPase protein often activated by RTKs. It plays a crucial role in cell proliferation and growth signaling pathways. Mutations in Ras are often associated with cancer development.

The MAP kinase pathway is a cascade of protein kinases activated by Ras. It plays a central role in cell growth and proliferation, relaying mitogenic signals from the cell surface to the nucleus.

Cell signaling pathways can be interconnected and complex. Different combinations of signals can activate multiple pathways simultaneously, leading to diverse cellular responses depending on the specific context.

Cell surface receptors relay extracellular signals via intracellular signaling pathways.

Intracellular receptors bind signaling molecules inside the cell, while cell surface receptors bind signaling molecules outside the cell.

Ion-channel-coupled receptors, G-protein-coupled receptors (GPCRs), and enzyme-coupled receptors are the three major classes of cell surface receptors.

Ion-channel-coupled receptors are transmembrane proteins that change the permeability of the plasma membrane to specific ions when activated.

G-protein-coupled receptors (GPCRs) are a large family of transmembrane proteins that activate trimeric G proteins upon binding their ligand.

GPCRs are activated by a diverse range of signaling molecules, including hormones, neurotransmitters, light, and odorants.

Trimeric G proteins are composed of alpha (α), beta (β), and gamma (γ) subunits. The α subunit binds GTP and GDP, and its activation state determines downstream signaling.

Activated G proteins activate downstream effector proteins, such as adenylyl cyclase and phospholipase C.

Adenylyl cyclase converts ATP to cAMP, a second messenger involved in various cellular processes.

Phospholipase C hydrolyzes PIP2, generating two second messengers: IP3 and DAG.

IP3 binds to calcium channels in the ER, releasing calcium ions into the cytoplasm.

DAG activates protein kinase C, a key regulator of various cellular processes.

Second messengers are small intracellular signaling molecules that relay the signal from activated receptors to downstream effector proteins.

Calcium ions (Ca2+) act as a second messenger and play a crucial role in various cellular functions including muscle contraction, neurotransmitter release, and gene expression.