33 terms

Lesson 2 Chapter 5 Chemical Messengers/Signal Molecules

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Four functions of chemical messengers
Paracrine
Autocrine
Neurotransmitter
Hormone
Paracrines
Signals to a NEARBY cell. Eg. growth factors, clotting factors, cytokines(peptides), histamine
Autocrines
Signals the same cell that secreted it. Signals itself. Eg. alpha2 adrenergic receptor (autoreceptor). Example of negative feedback
Neurotransmitter
Messenger produced and released BY NEURONS (into the ECF of the synaptic cleft)
Hormones
Messenger produced and released BY ENDOCRINE cells. releases into BLOODstream via interstitial fluid
Lipophilic Ligand
lipid soluble, bound to carrier, crosses cell membrane, receptor WITHIN cell(cytosol) or nucleus, response via GENE ACTIVATION, SLOW onset, LONG-LASTING response
Lipophobic Ligand
Water soluble, does NOT cross cell membrane easily (req. pumps/channels), receptor ON MEMBRANE, response via enzyme activation and membrane permeability. FAST onset, SHORT-lasting response
Which ligands trigger intracellular mediated responces?
Lipophilic ligands
Which ligands trigger membrane-bound receptor mediated responces? (Channel-linked receptors, enzyme-linked receptors, g-protein-linked receptors
Lipophobic ligands.
Are steroids hydrophobic or philic?
Steroids are derived from cholesterol so they are hydroPHOBIC (and lipophilic) thus they diffuse accross the plasma membrane
Cortisol and thyroid hormones have what in common?
They have intracellular receptors (they are lipid-soluble hormones)
Are G Proteins second messengers?
No, second messengers must leave the plasma membrane to relay the message to the inside of the cell. G proteins never leave the plasma membrane.
Beta Receptors
G-protein linked receptors, subclass of adrenergic receptors
Gi and Gs proteins
i inhibits enzyme activity, s stimulates enzyme activity
Phospholipase C converts ___ to ___ and ___
Phospholipase C converts PIP2 to diacylglicerol (DAG) and inositol triphosphate (IP3) which are both second messengers
Nervous System communication involves?
involves opening and closing of ion channels (ligand-gated) which is very fast and of short duration
Adenylate Cyclase
An enzyme that is associated with the cAMP signal transduction pathway
Lipophobic
Can NOT cross cell membrane without help
Lipophilic
CAN cross cell membrane without help
Channel-linked receptors
FAST, ligand-gated channels, the receptor and its channel are the same protein.
Enzyme-linked receptors
direct action, ligand binding activates ENZYME (eg:: tyrosine kinase that binds phosphate to tyrosine is activated)
What do kinases do?
phosphorylation. uses ATP and returns ADP
G-protein linked receptors
bind Guanosine nucleotides, regulatory proteins, link messengers to amplifier enzymes, slow ligand-gated channels (moves down the membrane to the channel
Difference between first and second messengers
first messenger: from the ECF, binds to outside of membrane (EXTRAcellular)
second messenger: product of amplifier enzyme (eg: adenylate cyclase produces cAMP which is the second messenger), INTRAcellular, wants to amplify the signal
cAMP
what is the second messenger?
A: Messenger
B: G-protein, GDP to GTP
C: Adenylate cyclase uses ATP
D: cAMP second messenger
cAMP activates protein kinase A
Name the molecules
What does adenylate cyclase do?
Activated by G-protein, uses ATP to make cAMP (Second messenger) which activates Protein kinase A which uses ATP to phosphorylate proteins.
Signal amplification
characteristic of second messengers, small amounts of ligand can have a huge response in target
cGMP
a second messenger that is triggered by Guanylate cyclase and triggers protein kinase G
How does Calcium act as a second messenger?
released from inside the cell, Ca+2 binds to Calmodulin and other Ca+2 binding proteins to alter protein activity
What is IP3's role in the Phosphatidylinositol system?
Activated by Phospholipase C (PIP2 ---> IP3 +DAG), IP3 (Inositol triphosphate) goes into the cytosol and triggers a receptor on the Endoplasmic Reticulum that triggers Ca+2 secretion. Ca+2 then triggers Calmodulin which then triggers protein kinases. Responce in cell is contraction.
What is DAG's role in the Phosphatidylinositol system?
Activated by Phospholipase C (PIP2 ---> IP3 +DAG), DAG (Diacylglycerol) stays in the plasma membrane to trigger Protein Kinase C which phospholrylates proteins to trigger a responce in the cell.
What are the A, G and C systems?
A = Adenylate cyclase and cAMP and Protein Kinase A
G = Guanylate cyclase and cGMP and Protein Kinase G
C = Phospholipase C and Ca+2, and PIP2 --> DAG and IP3, and Protein Kinase C
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