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Principles - Pharmacology > The Biochemical Basis for Therapy: Receptors and Signalling > Flashcards

The Biochemical Basis for Therapy: Receptors and Signalling Flashcards

1
Q

What are receptors?

A

The sensing elements of chemical communication

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2
Q

What are receptors the targets of?

A

Neurotransmitters
Hormones
Other mediators
Many therapeutic agents

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3
Q

What is autocrine signalling?

A

A cell signals to itself

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4
Q

What is paracrine signalling?

A

A cell signals to its close neighbours

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5
Q

What is endocrine signalling?

A

A cell signals via molecules transported by the blood to target distant cells

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6
Q

What are the four types of receptors?

A

Ligand-gated ion channels
G protein-coupled receptors
Kinase-linked receptors
Nuclear receptors

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7
Q

What are ligand-gated ion channels targeted by and what time scale is the action on?

A

Hydrophilic signalling molecules

Milisecond

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8
Q

Where are ligand gated channels located?

A

Plasma membrane

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9
Q

Where are G protein-coupled receptors located?

A

Plasma membrane

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10
Q

What are G protein-coupled receptors targeted by and what time scale is the action on?

A

Hydrophobic signalling molecules

Second

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11
Q

Where are kinase-linked receptors located?

A

Plasma membrane

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12
Q

What are kinase-linked receptors mainly targeted by and what time scale is the action on?

A

Hydrophilic protein mediators

Hours

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13
Q

What are nuclear receptors mainly targeted by and what time scale is the action on?

A

Hydrophobic signalling molecules

Hours/day

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14
Q

Where are nuclear receptors located?

A

Intracellularly in the nucleus or cytoplasm

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15
Q

What are ion channels?

A

Transmembrane pores formed by glycoproteins that span the membrane to create an ion conducting pathway for selected ions

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16
Q

What are ion channels usually regulated by and what do they cause?

A

Signals that cause the channel to cycle reversibly between a closed state and open conformation

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17
Q

What is the cycle ion channels go through between their closed state and open confirmation known as?

A

Gating

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18
Q

What movement occurs when ion channels are open and what is the rate of movement?

A

Passive diffusion

Rapid

19
Q

What may ion channels be gated by?

A

Chemical signals
Transmembrane voltage
Physical stimuli

20
Q

What is a classic example of a ligand gated channel?

A

The nicotinic acetylcholine receptor of skeletal muscle and neurones

21
Q

What is the sequence of ligand-gated ion channel activation?

A

Agonist binds - conformation change
Channel opens - conduction pathway for selected ions
Ions flow down concentration gradient

22
Q

What movement does the nicotinic acetylcholine receptor allow?

A

Movement of Na+ into the cell and simultaneous movement of K+ out of the cell, causing membrane depolarisation and excitation

23
Q

What do most cell surface receptors signal via?

A

Second messenger systems

24
Q

What happens in second messenger systems?

A

Receptor activation modulates the activity of an effector that is generally an enzyme

25
Q

What are G protein-coupled receptors?

A

Receptors linked to a cell membrane located effector by intermediary G proteins

26
Q

What do enzyme effectors do?

A

Increase or decrease their rate of synthesis of second messenger molecules affecting the activity of targets within the cell

27
Q

What is the process of signal to a response via a G protein-coupled receptor?

A 
Signal
Receptor
G protein
Effectors activate an enzyme
Second messenger
Cellular targets
Response
28
Q

What is the basic structure of a G protein-coupled receptor?

A

Integral membrane protein
Single polypeptide with extracellular NH2 and intracellular COOH
7 transmembrane alpha-helical spans joined by 3 extracellular and 3 intracellular connecting loops

29
Q

What is the basic structure of a G protein?

A

Peripheral membrane protein
3 polypeptide subunits - alpha, beta and gamma
Guanine nucleotide binding site in the alpha subunit that can hold guanosine triphosphate (GTP) or guanosine diphosphate (GDP)

30
Q

How are G proteins activated?

A

Agonist binding to the G protein-coupled receptor to which they preferentially coulple

31
Q

What occupies the inactive guanine nucleotide binding site of the alpha-subunit?

A

GDP

32
Q

What occupies the active guanine nucleotide binding site of the alpha-subunit and what does this cause?

A

GTP

The alpha and beta-gamma subunits dissociate from each other

33
Q

What occurs after the activation of a G protein-coupled receptor by an agonist?

A

Conformational change which is transmitted to the G protein alpha-subunit.
This releases GDP and allows GTP to bind in its place
The alpha-subunit separates from the receptor and beta-gamma-dimer.
It generates a free GTP-bound alpha-subunit and beta-gamma-dimer, which are both signalling units.

34
Q

What is the guanine nucleotide exchange?

A

Where the alpha-subunit releases GDP and allows GTP to bind in its place

35
Q

What is subunit dissociation?

A

Where the alpha subunit separates from the receptor and beta-gamma-dimer

36
Q

After activation of a G protein-coupled receptor, what happens before the signal is switched off?

A

The G protein dissociates into separates alpha and beta-gamma subunits and the alpha subunit combines with and modifies the activity of the effector.
The agonist may dissociate from the receptor but the signal can persist.

37
Q

How is a G protein-coupled receptor’s signal switched off?

A

The alpha-subunit acts as an enzyme - a GTPase - to hydrolyse GTP to GDP and Pi and the signal is turned off.
The G protein alpha subunit recombines with the beta-gamma subunit

38
Q

What does activation of a Gs or Gi protein by noradrenaline do?

A

Increases heart rate and force

39
Q

What does activation of a Gs or Gi protein by acetylcholine do?

A

Decreases heart rate and force

40
Q

What does activation of a Gg protein by noradrenaline do?

A

Causes vascular smooth muscle contraction

41
Q

What is an example of one form of signalling via receptor kinases?

A

The receptor for insulin

42
Q

What are nuclear receptors?

A

Ligand-gated transcription factors

43
Q

How do steroid hormones enter cells and what is this called?

A

Diffusion across the plasma membrane

Lipophilic

44
Q

What is the process of signalling via class 1 nuclear receptors?

A

Steroid hormones enter cells by diffusion across the membrane
They combine with an intracellular receptor to produce dissociation of inhibitory HSP proteins
The receptor steroid complex moves to the nucleus, forms a dimer and binds to hormone response elements in DNA
The transcription of specific genes is switched on or off to alter mRNA levels and the rate of synthesis of mediator proteins

Principles - Pharmacology (3 decks)

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