Topic 2 Flashcards
(101 cards)
What is a signal transduction pathway?
A sequence of molecular events and chemical reactions that lead to a cell’s response to a signal.
What are the three steps of a typical cell signaling process?
Signal reception, signal transduction, cellular response.
What role do receptors play in cell signaling?
Receptors specifically bind signaling molecules (ligands) and initiate the cell’s response.
What are the four main types of chemical signals in multicellular organisms?
Autocrine, juxtacrine, paracrine, and endocrine (hormones).
Define autocrine signaling.
Signaling where the cell releases a molecule that binds to receptors on its own surface.
What is juxtacrine signaling?
Direct cell-to-cell communication through adjacent contact, such as through gap junctions.
Define paracrine signaling.
The release of signals that diffuse locally and affect nearby cells.
What is endocrine signaling?
Long-distance signaling in which hormones are transported via the circulatory system.
What determines if a cell can respond to a particular signal?
The presence of the appropriate receptor protein.
What is ligand specificity?
A receptor’s ability to bind only a specific signaling molecule.
What is the Law of Mass Action as applied to receptors?
Reversible binding between a receptor (R) and a ligand (L): $$R + L \rightleftharpoons RL$$
What does a small dissociation constant ($$K_D$$) indicate about a receptor-ligand interaction?
High affinity between receptor and ligand.
Where are cell-surface receptors found?
In the plasma membrane.
What types of molecules typically bind intracellular receptors?
Small, hydrophobic molecules like steroid hormones.
List the main classes of membrane receptors.
Ion channel receptors, protein kinase receptors, G protein-coupled receptors.
How do ligand-gated ion channels work?
Ligand binding causes the channel protein to change shape, opening the channel and allowing ions to pass.
What is a kinase?
An enzyme that adds a phosphate group (phosphorylates) itself or another protein.
How does the insulin receptor function?
It acts as a protein kinase receptor, phosphorylating itself and cytoplasmic targets when insulin binds.
What is a G protein-coupled receptor (GPCR)?
A membrane receptor that activates a G protein when ligand binds, initiating a downstream signaling cascade.
Describe the basic G protein signaling cycle.
Ligand binding → receptor activates G protein (GDP → GTP) → G protein activates effector → cellular response.
What is a second messenger?
A small molecule that mediates and amplifies a signal inside the cell (e.g., cAMP, IP$_3$, Ca$^{2+}$).
How is cAMP produced?
ATP is converted into cAMP by adenylyl cyclase.
What is the function of protein phosphorylation in signal transduction?
It can activate or inhibit proteins, often amplifying the cellular response.
Why does signal amplification occur in most signaling pathways?
One signal molecule can activate multiple intermediates, increasing the response magnitude.
