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BIOC3560 > Biological Signalling: General + Types of Signal Transducers > Flashcards

Biological Signalling: General + Types of Signal Transducers Flashcards

1
Q

What are the 4 Characteristics of Signal Transduction Pathways:

A
  1. Specificity and Sensitivity
  2. Amplification
  3. Desensitization and Adaptation
  4. Integration
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2
Q

Signal transduction: Specificity

A

signal molecule fits the binding site on its complementary receptor
other signals do not fit

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3
Q

Increased specificity = ____ binding = ___ Kd

A

tight binding

low Kd

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4
Q

Additional features to increase specificity in cells?

A
  • specific receptors depending onthe cell
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5
Q

Signal transduction: sensitivity: 3 factors

A
  • high affinity of receptors for signal molecules
  • cooperativity in ligand receptor interaction
  • amplification of signal by enzyme cascades
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6
Q

What does a high affinity of receptors mean in terms of concentration of ligands needed and activation response?

A
  • high affinity for receptors to bind means

- low concentration of ligand necessary to elicit a large activation response

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7
Q

Signal transduction: Amplification

A
  • enzymes activate enzymes

- number of affected molecules increases geometrically in an enzyme cascade

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8
Q

Signal transduction: Desensitization / Adaptation

A
  • receptor activation triggers feedback circuit

- that shuts off receptor or removes from cell surface

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9
Q

Protein kinases that phosphorylate and increase downstream protein kinases (kinase cascade) is an example of which signal transduction characteristic?

A
  • amplification
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10
Q

How are kinase cascades decreased?

A

protein phosphorylase removes phosphate

this shuts down the kinase cascade until stimulus reaches below a threshold

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11
Q

Signal Transduction: Integration

A
  • two signals have opposite effects on metabolic characteristic
  • regulatory net outcome (input from both receptors) elicits the response
  • unified response appropriate to needs of organism
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12
Q

Types of signal transductors:

A
  • G protein coupled receptor
  • receptor tyrosine kinase
  • receptor guanylyl cyclase
  • gated ion channel
  • adhesion receptor
  • nuclear receptor
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13
Q

G protein coupled receptor

A
  • ligand binds receptor
  • activates GTP binding protein
  • regulates enzyme that generates secondary messenger
    i. e. adrenaline receptor -> PKA
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14
Q

Receptor tyrosine kinase

A
  • ligand binding activates tyrosine kinase
  • autophosphorylation
  • i.e. insulin receptor
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15
Q

Gated ion channel

A
  • open/close channels in response to concentration of signal ligand or membrane potential
    i. e. Ach receptor
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16
Q

Two types of neurotransmitters for ionotropic receptors:

A
  • biogenic amines

- amino acids

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17
Q

Which biogenic amines give a positive effect to nerve transmission?

A
  • acetyl choline
  • nicotinic receptors
  • muscarini c receptors (M1-5)
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18
Q

What is Ach and what does it do?

A
  • main neurotransmitter for nerve-muscle (voluntary); CNS; parasympathetic (involuntary)
19
Q

What do nicotinic receptors do?

A
  • triggers Na+ and Ca+ inflow (down gradient)
  • depolarize
  • activation [nicotine]
20
Q

Which biogenic amines give a negative effect to nerve transmission?

A
  • Gamma-aminobutyric acid (GABA)

- a major inhibitory NT in the CNS

21
Q

What do GABA receptors do?

A
  • inhibit NT in CNS
  • triggers influx of Cl- (recall Cl- is high outside)
  • hyperpolarizing (cuz too negative inside)
  • inactivation [tranquilizers, alcohol, barbiturates]
22
Q

Which amino acid neurotransmitters for ionotropic receptors give a positive effect?

A
  • glutamate

- AMPA, Kainate, NMDA, delta receptors

23
Q

What does glutamate do?

A

major NT in CNS

24
Q

What do the AMPA, Kainate, NMDA, delta receptors do?

A
  • triggers Na+ and Ca2+ influx
  • depolarize
  • involved in learning, memory, plasticity
    [antipsychotics, anti-schizophrenia]
25
Q

Which amino acid neurotransmitters for ionotropic receptors give a negative effect?

A
  • Glycine
26
Q

What doe glycine receptors trigger?

A
  • Cl- influx
  • hyperpolarize
  • inactivation
27
Q

Nicotinic acetylcholine receptor (AchR) - how do electrical signals travel

A
  • passage of electrical signal from motor neuron to muscle fiber at neuromuscular junction
28
Q

How is acetylcholine released and bound?

A
  • released by motor neuron
  • diffuse to plasma membrane of myocyte
  • binds AchR
29
Q

How is a muscle contraction triggered?

A
  • Ach bound
  • conformational change in AchR = open
  • inward movement of Ca2+ and Na+
  • triggers muscle contraction
30
Q

In the first step of neural transmission, what does Ach cause?

A
  • ach opens ach receptors (ligand gated Na+ Ca2+ channel)
  • Na+ flows in (down gradient)
  • small depolarization (-70 to -40mV)
31
Q

Explain the repolarizing dip.

A
  • K+ channels repolarize causes the drop in membrane potential
  • the K+ flow out of the cell (down gradient) -75mV
  • the K+ channels inactivate -60mV
32
Q

What is the wave that travels along the axon?

A
  • wave of depolarization and repolarization

along axon

33
Q

What is the process that releases neurotransmitters into the synaptic cleft?

A
  • exocytosis

- which then causes the small depolarization…

34
Q

How many subunits does AchR have?

A

5

35
Q

How many helices does each subunit of AchR have?

A

4

36
Q

AchR is a ____ gated channel

A

ligand gated (Ach)

37
Q

Where are the M2 helices located?

A

The M2 helix in the 5 subdomains face the interior of the channel.

38
Q

What is the facing of the M2 helices when the channel is closed?

A

bulky, hydrophobic
Leucine residues
face the interior of the channel

39
Q

What is the unique property of M2

A

amphipathic

hydrophobic leucine on one side, but has polar residues on other side

40
Q

What triggers the twist?

A

2 Acetylcholines bind

41
Q

What twists when Ach binds?

A

the 5 subunits each twist

- “Quaternary Twist” to open the pore

42
Q

What happens when the subunits twist?

A

the M2 helices expose the negative groups

  • small, polar residues line the channel
  • allows anything that is positive to flow in - no selectivity for Na+ Ca2+ K+
  • depolarize (Na+ and Ca2+ can flow in)
43
Q

What is an example of something that blocks AchR?

A
  • tubocurarine
  • poison darts
  • can’t breath, death
  • also used in surgery as a muscle relaxant

BIOC3560 (6 decks)

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