Chapter 5: Control of cells by chemical messengers Flashcards Preview

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Flashcards in Chapter 5: Control of cells by chemical messengers Deck (35):

Intracellular Chemical messengers

- include hormones and neurotransmitters
- require chemical messenger binds to specific receptors on target cells and requires signal transduction proceeds, sequence of intracellular events in response to chemical messengers


Receptor composition

- proteins and glycoproteins


receptor locations

- plasma membrane (interact with water-soluble/transmembrane chem messengers)
- nucleus (interact with lipid-soluble chem messengers)


receptor specificty

- only specific receptors will bind particular chemical messengers
- mostly bind with only 1 chemical messenger
- different cell types possess receptors for particular messengers (ligands)
- different cell types may have receptors for the same chemical messenger
- a single cell type may contain more than one receptor type for a single messenger


receptor affinity

- can have different affinity for different chemical messengers


receptor saturation

- may be saturated via chemical messengers


receptor competition

- antagonists and agonists



- binds to a receptor
- does NOT trigger cell's response
- blocks the receptor from binding to its proper chemical messenger
- example: beta blocker



- binds to receptor
- triggers the cell's response
- mimics the messengers response


Down regulation

- decrease in total number of target cells receptors for a given messenger
- response to chronic high extracellular messenger concentration


Up regulation

- increase in total number of target-cell receptors for a given messenger
- response to chronically low extracellular messenger concentration
- supersensitivity


mechanisms in which up/down regulation occurr

- receptor synthesis or degredation
- alterations in gene expression --> code for receptors


signal transduction pathways

- sequence of events leading to ultimate cellular response
- initiated by receptor activation


receptor activation

- change in the conformation of the receptor induced by binding of chemical messenger


types of cellular responses

- changes in the permeability, transport properties, or electrical state of the cell's plasma membrane
- changes in the cell's metabolism
- changes in the cell's secretory activity
- changes in the cell's rate of proliferation or differentiation
- changes in contractile activity


signal transduction pathways initiated via lipid-soluble messengers

- steroid hormones, thryoid hormones, 1,25-dihydroxy vitamin D
- involve intracellular receptors most located in nucleus (in cytoplasm too, but rare)
- activation alters rates of gene transcription


signal transduction pathways initiated via water-soluble messengers

- most hormones, neurotransmitters, and paracrine/autocrine compounds
- receptors are located in the plasma membrane
- 4 types of receptors:
1) receptors are ligand-gated channels
2) receptors are ions
3) receptors are bound to and activate JAK kinases
4) G-protein-coupled receptors



the intracellular chemical messenger that binds to the plasma membrane receptor (hormone or neurotransmitter)



- a substance that enters or is generated in the cytoplasm in response to receptor activation by the first messenger; serves as a chemical relay to the interior of the cell


receptors that are ligand-gated ion channels

- receptor activation by a first-messenger --> conformational change in the receptor --> opens the channel through the plasma membrane
- increased diffusion of one or more types of ions across the plasma membrane (change in the mem potential)
- increased cytosolic calcium concentration is important in many signal transduction pathways


Receptors that function as enzymes

- majority are receptor tyrosine kinases!


Mechanism of action of receptors function as enzymes

- receptor activation
- conformational change
- activation of enzymatic portion of the receptor
- autophosphorylation
- formation of phosphotyrosines
- phosphotyrosines serve as docking sites for cyotoplasmic proteins (docking proteins)
- bound docking proteins bind and activate other proteins, which activates one or more signaling patways
- cellular response (usually an effect on cell proliferation or differentiation)


exception with receptors as enzymes

- receptor acts as a guanylyl cyclase
- catalyzes formation of cyclic GMP (cGMP) in the cytoplasm
- cGMP acts as a second messenger, activates cGMP-dependent protein kinases that phosphorylates proteins involved in the transduction pathway (cells response)
- found in large amounts in the retina; involved in processing visual inputs


Receptors that interact with cytoplasm JAK kinases

- receptor is associated with cytoplasmic JAK kinase (tyrosine kinase) --> function as a unit


mechanism of action of receptor with cytoplasm JAK kinase

- binding of first messenger
- conformational change in receptor
- activates JAK kinase
- JAK kinase phosphorylates a protein or proteins (many act as transcription factors)
- synthesis of new proteins that mediate cell's response


G-protein-coupled receptors

- largest category
- g-protein complex located on the cytoplasmic surface of the plasma membrane is bound to receptor


mechanism of action of g-protein-coupled receptors

- binding of a first messenger to receptor activates it
- change in receptor conformation
- increased affinity of alpha subunit of g protein for GTP
- GTP binds to alpha subunit
- dissociation of the alpha subunit from g-protein complex
- alpha subunit links to another plasma membrane protein (plasma membrane effector protein)


Gs vs Gi proteins

- Gs: activate adentltl cyclase --> cAMP production
- Gi : inhibit adentltl cyclase activity --> decrease cAMP production


phospholipase c, diacylglycerol, and inositol triphosphase mechanism of action

- receptor activation by 1st messenger
- activation of Gq
- activation of phospholipase C
- catalyses breakdown of PIP2 into diacyglyerol and inositol triphoshate which become second messengers in cell
- diacyglycerol activates protein kinase C enzymes that phosphorylate other proteins --> cells response
- IP3 binds to receptors (ligan gated Ca++ channels) on endoplasmic reticulum which open channels and calcium diffuses out of ER into the cytoplasm --> biochem events --> cells respons


control of ion channels by G proteins

- direct gprotein gating
- indirect gprotein gating


calcium as second messenger

- plasma membrane Ca++ channels can be ligand-gated or voltage-gated
- calcium acts as second messenger by binding to various cytosolic proteins and altering their conformation


cyclooxygenase inhibitors

- asprin and nonsteroidal anti-inflamm drugs
- inhibit production prostoglandins and thromboxates
- steroids inhibit phospholipase A2



- stimulate inflammation and in immune response
- drugs act to inhibit production of eicosanoids by inhibiting cyclooxygenase or phospholipase A2
- generated by poly-unsaturated acid which is part of membrane phospholipids
- first messenger binds to receptor activating phospholipase A2
- A2 splits off arachondonic acid from membrane phospholipids
- arachodonic acid is metabolized in 2 ways


arachodonic acid metabolized

1) acted on by enzyme lipo-oxygenase --> lucotryannes
2) acted on by enzyme cyclo-oxygenase --> cyclic endoproxide--> either prostaglandin or thromboxates


receptor activation ceases in signal transduction pathways

- decrease in amount of first messengers
- receptor inactivation
--> chemically alteres (phosphorylated)...lower its affinity for the first messenger or prevent G-protein binding
- internalized by endocytosis