Biological signalling Flashcards
What are the 2 types of intercellular signalling
- Signalling by secreted molecules to receptor on target cell
- Signalling by plasma membrane-bound molecules
Signalling between plasma membrane proteins
What are the three types of signalling by secreted molecules?
- Paracrine
- Endocrine
- Synaptic
Paracrine signalling
- The signalling between cells within a tissue
- A local mediator is released by a cell and is received by an adjacent cell within the tissue
Give 2 examples of intracellular receptors
- Steroid hormones
- Thyroid hormones
Endocrine
Hormone produced by gland travels through blood to act on distant target cell
Synaptic signalling
Nerve cell secretes neurotransmitter at synapse to target cell
What are the subdivisions of signalling molecules
- Local chemical mediators
- Hormones
- Neurotransmitters
Note: this classification, while still useful, no longer holds
What are the 2 types of receptors?
- Cell surface receptors (hydrophilic molecules can’t cross membrane, transported in blood via carrier)
- Intracellular receptors (small hydrophobic molecules can cross)
What is a receptor?
A receptor is a molecule that recognises specifically a second molecule (ligand) or family of molecules and which in response to ligand binding brings about regulation of a cellular process
response to ligand binding brings about regulation of cellular process
How do you describe a receptor in it’s unbound state?
It is functionally silent
What is a ligand?
Any molecule that binds specifically to a receptor site
What are the 2 types of ligand?
What does each one do?
1) Agonist
2) Antagonist
An agonist = binds to activate a receptor
An antagonist = binds but doesn’t activate the receptor (prevents agonist binding)
Give 8 roles of receptors
- Signalling by hormones/local chemical mediators
- Neurotransmission
- Cellular delivery
- Control of gene expression
- Celladhesion
- Modulation of the immune response
- Sortingofintracellularproteins
- Release of intracellular calcium stores
What is the binding affinity of receptors like?
Compared to what?
Ligand - very high affinity (Kd)
Compared to the binding of substrates and allosteric regulators to enzyme sites (Km)
Enzyme - lower (Km)
How are receptors classified?
Specific Agonist recognised (eg Ach receptor) Sub-classified by affinity for antagonists (eg nAchR)
Acetylcholine receptors: Receptor types and and agonists
Muscarinic (muscarine)
Muscarinic receptor subtypes and antagonists
M1 - pirenzipine
M2 - Gallamine
M3 - Hexahydrosiladiphenol
Receptor vs Acceptor
- Receptors are silent at rest (no activity)
- Agonist binding stimulates a biological response
- Acceptors operate in absence of a ligand (need ligand binding and something else)
- Ligand binding alone produces no response
Acceptors and modulator - watch lecture
Dihydrofolate reductase - Methotrexate
Sodium channel - Local anaesthetic, neurotoxins
How has evolution solved the problem of transducing extracellular into intracellular signals? - watch lecture
Developed transducing protein to form 2nd messenger
Types of signal transduction receptors (4)
- Membrane-bound receptors with integral ion channels
- Membrane-bound receptors with integral enzyme activity
- Membrane-bound receptors which couple to effectors through transducing proteins
- Intracellular receptors
What are the 5 methods of tranducing extracellular into intracellular signals?
-Receptor has intracellular enzyme
-Recpetor opens channel
-Receptor coupled to effector
-Receptor coupled to transducing molecule
-Hydrophobic signal to intracellular receptor
Describe the structure of a classic receptor family and give an example
5 subunits (2a, b, gamma and delta) The subunits make a pore Closed pore when silent
( nicotinic acetylcholine receptor (nAchR) is an example)
Name 3 Membrane bound receptors with a classic receptor family with integral ion channels and state the receptor and the ion selectivity
Name 1 Membrane bound receptors with a classic receptor family with integral ion channels and state the receptor and the ion selectivity
What is the structure of an MBR with integral enzyme activity?
2 domains: Binding domain (extracellular) Catalytic domain (intracellular)
1) What are some examples of Membrane Bound Receptors with integral enzyme activity?
2) Describe their integral enzyme activity
3) Give examples
1) - ANP (atrial natruiretic peptide) receptor
2) linked directly to guanylyl cyclase
3) GTP –> cGMP
1) Growth factor receptors
2) linked directly to tyrosine kinase
3) Insulin, epidermal growth factor (EGF) platelet-derived growth factor (PDGF)
How does signalling occur via tyrosine kinase linked receptors? - watch lecture
- Agonist binds to tyrosine causing autophosphorylation
- Tyrosine kinase activates enzymes (via direct phosphorylation)
- or transducing proteins (transducers recognise phosphorylated tyrosine)
Structure of insulin receptor
Insulin binding domain (extracellular)
Transmembrane domain in the plasma membrane
Tyrosine kinase domain (inside)
Tyrosine kinase domain (inside)
What are membrane bound receptors that signal through transducing proteins known as?
Seven transmembrane domain receptors (7TMD)
What are some examples of transducing proteins?
- Adrenaline binds to β-adrenoceptors which activates ATP cAMP via the G-protein Gs
-ACh binds to M2 muscarinic ACh receptors wihich stimulates K+ channel opening via the G-protein Gi
What is the structure of transducing proteins?
7 transmembrane domains
-coupled through G proteins to enzymes of channels
-folded structure-lignad binds in pore
How are 7TMD receptors how coupled?
Coupled through GTP-binding regulatory proteins (G-proteins) to enzymes or channels
What occurs when adrenaline binds to b adrenoreceptors?
activates enzyme adenylyl cyclase
increase in cAMP
via Gs protein
What happens when acetylcholine binds to M2 muscarinic receptors?
Stimulates K+ channel opening via Gi protein (suppress electrical activity)
via Gi protein
Structure of G protein coupled receptor
Binding domains: extracellular or within membrane
G coupled protein domains within cell
Form cleft around ligand
What occurs when ligand binds to G coupled receptor?
GDP is replaced by GTP
a and b subunits disassociate
What do G-proteins do?
- integrate signals
- cause amplification
Type of signalling G protein coupled receptors can achieve
Inhibitory response
Stimulatory response
Intracellular receptor structure
Binding domain
DNA binding domain
(within cell)
How are intracellular receptors activated?
Inhibitory protein complex covers DNA binding site on receptor
Hormone binds to binding site
Conformational change = Inhibitory protein removed
DNA binding site exposed
= alter transcription
Superfamily receptors
Intracellular = steroid and thyroid (have homology/similar structure)
Amplification in G coupled receptors
1 ligand binding can result in lots of G proteins activated
resulting in lots of 2nd messenger production
(amplification at each step)
What can cellular activation overall lead to?
Activation or Inhibition
eg insulin binds and stimulates glycogen synthesis
glucagon stimulates glycogen breakdown to glucose
In cardiac pacemaker cells, noradrenaline binds to … to … heart rate
noradrenaline binds to β1 adrenoceptors to increase heart rate
