Biological Signalling: General + Types of Signal Transducers Flashcards Preview

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Flashcards in Biological Signalling: General + Types of Signal Transducers Deck (43)
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1

What are the 4 Characteristics of Signal Transduction Pathways:

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

2

Signal transduction: Specificity

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

3

Increased specificity = ____ binding = ___ Kd

tight binding
low Kd

4

Additional features to increase specificity in cells?

- specific receptors depending onthe cell

5

Signal transduction: sensitivity: 3 factors

- high affinity of receptors for signal molecules
- cooperativity in ligand receptor interaction
- amplification of signal by enzyme cascades

6

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

- high affinity for receptors to bind means
- low concentration of ligand necessary to elicit a large activation response

7

Signal transduction: Amplification

- enzymes activate enzymes
- number of affected molecules increases geometrically in an enzyme cascade

8

Signal transduction: Desensitization / Adaptation

- receptor activation triggers feedback circuit
- that shuts off receptor or removes from cell surface

9

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

- amplification

10

How are kinase cascades decreased?

protein phosphorylase removes phosphate
this shuts down the kinase cascade until stimulus reaches below a threshold

11

Signal Transduction: Integration

- 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

12

Types of signal transductors:

- G protein coupled receptor
- receptor tyrosine kinase
- receptor guanylyl cyclase
- gated ion channel
- adhesion receptor
- nuclear receptor

13

G protein coupled receptor

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

14

Receptor tyrosine kinase

- ligand binding activates tyrosine kinase
- autophosphorylation
- i.e. insulin receptor

15

Gated ion channel

- open/close channels in response to concentration of signal ligand or membrane potential
i.e. Ach receptor

16

Two types of neurotransmitters for ionotropic receptors:

- biogenic amines
- amino acids

17

Which biogenic amines give a positive effect to nerve transmission?

- acetyl choline
- nicotinic receptors
- muscarini c receptors (M1-5)

18

What is Ach and what does it do?

- main neurotransmitter for nerve-muscle (voluntary); CNS; parasympathetic (involuntary)

19

What do nicotinic receptors do?

- triggers Na+ and Ca+ inflow (down gradient)
- depolarize
- activation [nicotine]

20

Which biogenic amines give a negative effect to nerve transmission?

- Gamma-aminobutyric acid (GABA)
- a major inhibitory NT in the CNS

21

What do GABA receptors do?

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

22

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

- glutamate
- AMPA, Kainate, NMDA, delta receptors

23

What does glutamate do?

major NT in CNS

24

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

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

25

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

- Glycine

26

What doe glycine receptors trigger?

- Cl- influx
- hyperpolarize
- inactivation

27

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

- passage of electrical signal from motor neuron to muscle fiber at neuromuscular junction

28

How is acetylcholine released and bound?

- released by motor neuron
- diffuse to plasma membrane of myocyte
- binds AchR

29

How is a muscle contraction triggered?

- Ach bound
- conformational change in AchR = open
- inward movement of Ca2+ and Na+
- triggers muscle contraction

30

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

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

31

Explain the repolarizing dip.

- 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

What is the wave that travels along the axon?

- wave of depolarization and repolarization
along axon

33

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

- exocytosis
- which then causes the small depolarization...

34

How many subunits does AchR have?

5

35

How many helices does each subunit of AchR have?

4

36

AchR is a ____ gated channel

ligand gated (Ach)

37

Where are the M2 helices located?

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

38

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

bulky, hydrophobic
Leucine residues
face the interior of the channel

39

What is the unique property of M2

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

40

What triggers the twist?

2 Acetylcholines bind

41

What twists when Ach binds?

the 5 subunits each twist
- "Quaternary Twist" to open the pore

42

What happens when the subunits twist?

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

What is an example of something that blocks AchR?

- tubocurarine
- poison darts
- can't breath, death
- also used in surgery as a muscle relaxant