3.2 Biosignaling Flashcards

1
Q

Ion Channels

A

proteins that create specific pathways for charged molecules

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2
Q

Facilitated diffusion

A
  • type of passive transport, is the diffusion of molecules down a concentration gradient through a pore in the membrane created by this transmembrane protein
  • used for molecules that are
    impermeable to the membrane (large, polar, or charged)
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3
Q

Ungated channels

A

have no gates and are therefore unregulated

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4
Q

Voltage-Gated Channels

A
  • the gate is regulated by the membrane potential change near the channel
    *Voltage-gated nonspecific sodium–potassium channels are found in cells of the sinoatrial node of the heart (serve as the pacemaker current; as the voltage drops, these channels open to bring the cell back to threshold and fire another action potential)
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5
Q

Ligand-Gated Channels

A
  • the binding of a specific substance or ligand to the channel causes it to open or close
    *neurotransmitters act at
    ligand-gated channels at the postsynaptic membrane
    *Membrane receptors may also display catalytic activity in response to ligand binding
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6
Q

How does Km relate to ion channels?

A

refers to the solute concentration at which the transporter is functioning at half of its maximum activity

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7
Q

Km and vmax parameters for ion channels?

A

Same Km and vmax parameters that apply to enzymes

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8
Q

Enzyme-linked receptors

A
  • have three primary protein domains: a membrane spanning domain, a ligand binding domain, and a catalytic domain
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9
Q

Membrane-spanning domain

A
  • anchors the receptor in
    the cell membrane
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10
Q

Ligand-binding domain

A
  • stimulated by the appropriate ligand and induces a conformational change that activates the catalytic domain which initiates a second messenger cascade
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11
Q

Functions of heterotrimeric G proteins

A
  • Gs stimulates.
  • Gi inhibits.
  • “Mind your p’s and q’s”: Gq activates phospholipase C.
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12
Q

G protein-coupled receptors (GPCR)

A
  • large family of integral membrane proteins involved in signal transduction
  • characterized by their seven membrane-spanning α-helices
  • receptors differ in specificity of the ligand-binding area found on the extracellular surface of the cell.
  • G proteins are named for their
    intracellular link to guanine nucleotides (GDP and GTP)
  • The binding of a ligand increases the affinity of the receptor for the G protein
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13
Q

3 main G proteins

A
  • Gs stimulates adenylate cyclase, which increases levels of cAMP in the cell
  • Gi inhibits adenylate cyclase, which decreases levels of cAMP in the cell
  • Gq activates phospholipase C, which cleaves a phospholipid from the
    membrane to form PIP2. PIP2 is then cleaved into DAG and IP3; IP3 can open calcium channels in the endoplasmic reticulum, increasing calcium levels in the cell
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14
Q

GPCR Activation Steps

A

In its inactive
form, the α subunit binds GDP and is in a complex with the β and γ
subunits. When a ligand binds to the GPCR, the receptor becomes activated
and, in turn, engages the corresponding G protein, as shown in Step 1 of Once GDP is replaced with GTP, the α subunit is able to
dissociate from the β and γ subunits (Step 2). The activated α subunit alters
the activity of adenylate cyclase. If the α subunit is αs, then the enzyme is
activated; if the α subunit is αi, then the enzyme is inhibited. Once GTP on
the activated α subunit is dephosphorylated to GDP (Step 3), the α subunit
will rebind to the β and γ subunits (Step 4), rendering the G protein inactive

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