Chapter 7 - Cell Communication Flashcards
Signal Transduction Pathway
Sequence of events that leads to a cell’s response to a signal; chemical signals reach target cells by local diffusion or by circulation through the blood; involves a signal (ligand), a receptor, and responses
Modes of signal delivery
Autocrine: signals diffuse to and affect the cells that make them; juxtacrine: signals affect only cells adjacent to the cell producing the signal; paracrine: signals diffuse to and affect nearby cells
Receptor protein
Holds very specific binding sites for signal molecules or ligands; binding of ligand causes the receptor protein to change conformation
Receptor protein inhibitors (antagonists)
Inhibitors can also bind to receptor proteins; ie. caffeine binds to adenosine receptors that does not allow the signal transduction pathway to reduce brain activity to occur
Crosstalk
Signal transduction pathways can be interrelated; pathways can branch and one activated receptor protein can activate multiple pathways; multiple pathways can converge on a single transcription factor; one pathway can be activated while another is inhibited
Responses to Signal Transduction Pathways
Involves enzymes, which catalyze biochemical reactions or involves transcription factors, which are proteins that turn the expression of particular genes on or off
Membrane receptors
Large or polar ligands cannot cross the lipid bilayer; the ligand binds to the cell membrane receptor, causing a conformation change on the inside of the receptor; the ligand does not enter the cell
Transduction of the Signal Transduction Pathway
The reaction to the ligand binding to the receptor protein; causes a chain of reactions, amplifying the signal, resulting in many intracellular changes
Ion Channel Receptors
Channel proteins that allow ions to enter or exit the cell; ; ie. acetylcholine receptor is a gated ion channel receptor that results in a series of reactions when a signal molecule bind to the receptor that ultimately leads to a muscle contraction
Signals
Can be ligands, sensory stimuli, hormones, neurotransmitters, odorants, nutrients, etc
Protein Kinase Receptors
When a ligand binds, it triggers the receptor to combine side by side with a nearby receptor protein to form a dimeric structure; the receptors autophosphorylate and phosphorylate response substrates, generating a chain of reactions
G Protein-Linked Receptors
aka G protein coupled receptors (GPCR); a signal binds to the 7-transmembrane domain receptor, causing a conformational change that binds and activates a three-subunit G protein; the activated G protein initiates the exchange of GDP for GTP; the GTP bound subunit detaches and binds to and activates a nearby effector protein that causes changes in cell function; after activation of the effector protein, GTP is hydrolyzed into GDP, which sends the G protein subunit back to its other 2 G protein subunits to start the cycle over again
Adenyl cyclase
The effector protein involved in the epinephrine G protein coupled receptor signal transduction pathway; once the GTP activated G protein subunit binds to adenyl cyclase, the enzyme catalyzes ATP into cAMP (a secondary messenger) that ultimately causes a cellular response to epinephrine (fight or flight mode)
Intracellular receptors
Small or nonpolar ligands diffuse across the lipid bilayer and bind to receptors located in the cytoplasm or in the nucleus; the receptor bound to the ligand acts as a transcription factor that moves to the nucleus where it binds to DNA and alters gene expression
Protein Kinase Cascade
Pathway in which one protein kinase activates the next causing a chain of reactions; at each step in the cascade of events, the signal is amplified, because each newly activated protein kinase is an enzyme that can catalyze the phosphorylation of many target proteins, providing variation in response; information that arrived at the plasma membrane is communicated to the nucleus; multiple steps provide specificity
