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ONLINE PHYSIOLOGY > Chapter 5: Control of cells by chemical messengers > Flashcards

Chapter 5: Control of cells by chemical messengers Flashcards

1
Q

Intracellular Chemical messengers

A
  • 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
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2
Q

Receptor composition

A
  • proteins and glycoproteins
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3
Q

receptor locations

A
  • plasma membrane (interact with water-soluble/transmembrane chem messengers)
  • nucleus (interact with lipid-soluble chem messengers)
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4
Q

receptor specificty

A
  • 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
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5
Q

receptor affinity

A
  • can have different affinity for different chemical messengers
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6
Q

receptor saturation

A
  • may be saturated via chemical messengers
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7
Q

receptor competition

A
  • antagonists and agonists
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8
Q

antagonist

A
  • binds to a receptor
  • does NOT trigger cell’s response
  • blocks the receptor from binding to its proper chemical messenger
  • example: beta blocker
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9
Q

agonist

A
  • binds to receptor
  • triggers the cell’s response
  • mimics the messengers response
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10
Q

Down regulation

A
  • decrease in total number of target cells receptors for a given messenger
  • response to chronic high extracellular messenger concentration
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11
Q

Up regulation

A
  • increase in total number of target-cell receptors for a given messenger
  • response to chronically low extracellular messenger concentration
  • supersensitivity
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12
Q

mechanisms in which up/down regulation occurr

A
  • receptor synthesis or degredation

- alterations in gene expression –> code for receptors

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13
Q

signal transduction pathways

A
  • sequence of events leading to ultimate cellular response

- initiated by receptor activation

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14
Q

receptor activation

A
  • change in the conformation of the receptor induced by binding of chemical messenger
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15
Q

types of cellular responses

A
  • 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
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16
Q

signal transduction pathways initiated via lipid-soluble messengers

A
  • 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
17
Q

signal transduction pathways initiated via water-soluble messengers

A
  • 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
18
Q

first-messenger

A

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

19
Q

second-messenger

A
  • 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
20
Q

receptors that are ligand-gated ion channels

A
  • 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
21
Q

Receptors that function as enzymes

A
  • majority are receptor tyrosine kinases!
22
Q

Mechanism of action of receptors function as enzymes

A
  • 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)
23
Q

exception with receptors as enzymes

A
  • 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
24
Q

Receptors that interact with cytoplasm JAK kinases

A
  • receptor is associated with cytoplasmic JAK kinase (tyrosine kinase) –> function as a unit
25
Q

mechanism of action of receptor with cytoplasm JAK kinase

A
  • 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
26
Q

G-protein-coupled receptors

A
  • largest category

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

27
Q

mechanism of action of g-protein-coupled receptors

A
  • 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)
28
Q

Gs vs Gi proteins

A
  • Gs: activate adentltl cyclase –> cAMP production

- Gi : inhibit adentltl cyclase activity –> decrease cAMP production

29
Q

phospholipase c, diacylglycerol, and inositol triphosphase mechanism of action

A
  • 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
30
Q

control of ion channels by G proteins

A
  • direct gprotein gating

- indirect gprotein gating

31
Q

calcium as second messenger

A
  • 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
32
Q

cyclooxygenase inhibitors

A
  • asprin and nonsteroidal anti-inflamm drugs
  • inhibit production prostoglandins and thromboxates
  • steroids inhibit phospholipase A2
33
Q

Eicosanoids

A
  • 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
34
Q

arachodonic acid metabolized

A

1) acted on by enzyme lipo-oxygenase –> lucotryannes

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

35
Q

receptor activation ceases in signal transduction pathways

A
  • 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

ONLINE PHYSIOLOGY (13 decks)

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