Unit 1 - Signal Transduction Flashcards
Molecular
activation of enzyme, generation/synthesis of metabolite and its degradation
cellular
number of mitochondria regulated in a cell may divide, split, fuse
tissue/organ
no of cells or cell types are tightly regulated
4 levels of regulation in living organism
molecular
cellular
tissue/organ
organism (neuro-endocrine)
main mechanims of integration of the levels of regulation
HPA axis
what is the target of regulation
definition of signal transduction
process linking the signal-activated receptor and the biological response
there is a common logic in the structure of signal transducers and in the mode of their function
how is regulation initiated and and how does it flow
initiated by the signal (information) reaching the cell or formed within the cell
EC signal molecule → receptor protein → IC signalling proteins → target proteins
what can a signal be, based on their origin
from environment - pin, temp, light, smell
from organism - hormones, cytokines, metabolites
from within the same cell - DNA damage, ROS
what can a signal be if chemical
- proteins - GH
- peptides - insulin, neuropeptides
- AAs, derivatives - thyroxine, dopamine, epinephrine
- lipids - PGs, platelet activating factor
- ions - Ca2+, Cl-
- nucleotides - adenosines with specialised receptors on their surface
- gases - nitric oxide (produced by endothelial cells – trigger smooth muscle relaxation and vasodilation)
types of signal transmission
what is the significance of ligand binding
specificity
amplification
co-ordination of response - the same receptor may be present on a number of cells
cell specific response - by regulating the number and function of receptors
example of disease that involves a cell-specific response
type 2 diabetes
autoinhibitory receptors are present on cells become inactivated and unresponsive
types of receptors
cell surface/transmembrane receptors
nuclear receptors
cytosolic receptors
receptors for what hormone are present on a wide variety of cells
cortisol
amplification system
Uniform response of cell
e.g. If a cell triggers lipid degradation, whole lipid synthesis across the cell has to shut down and lipid degradation must occur
Net 0 effect - what 1 process achieves, the other will undo
allosteric regulation
interconversion cycle
NOTE: enzyme specific - some are active phosphorylated, some are active dephosphorylated
Akt/Protein Kinase P interconversion cycle - 1st mechanism
inactive Akt → Akt by 2 mechanisms:
FIRST
phosphorylated serine 473 interacts with the linker between the kinase and pH domains
2nd mechanism in Akt/protein kinase P interconversion cycle
phosphorylated serine 477 and threonine 479 result in the displacement of the pH domains
enzyme cascade
acceptors
all signal transduction pathways culminate to control of function of proteins (mostly enzymes, ion channels, transporters), which are involved directly in formation of biological response
2 categories of acceptors
control of protein amount
gene expression
protein degradation
protein stabilisation (tumour suppression gene P53)
control of existing proteins
without covalent modification of the protein (P) - Allosteric activator binds to an allosteric enzyme complex
with covalent modification of the protein - reversible and irreversible (cleavage of 3 forms of enzymes e.g. digestive enzymes involved in cleavage of trypsinogen to inter trypsin)
tumour suppression gene P53
regulated by protein stabilisation
mechanisms of hormonal regulation
4 types of membrane bound receptors
ion channel enclosing receptors
7 transmembrane domain receptors
1 hydrophobic domain receptors (R with enzyme activity, R with no enzyme activity)
ligands that activate membrane bound receptors
hydrophilic
signalling via ion channel-enclosing receptor example
nicotinic ACh receptor
structure of nicotinic ACh receptor
binding results in
pentamer (2 x α, β, γ, δ)
subunits surround a central pore
2 Ach binding sites from the pore
their binding is co-operative and leads to channel opening
channel is selective for divalent cations (+ve) - Na+ and Ca2+
hyperpolarisation with AP triggered
ION CHANNEL-ENCLOSING RECEPTORS
GABA, glycine, ACh, glutamate, serotonin
- receptors
- amplification systems
- acceptors
- biological response
- on the plasma membrane
- channel-transmitted ions
- membrane ion channels (e.g. VG Na+ channels)
- membrane depolarisation, hyperpolarisation, muscle contraction etc
glycine ion selectivity
Cl-
HCO3-
GABA ion selectivity
Cl-
HCO3-
ACh ion selectivity
Na+
K+
Ca2+
glutamate ion selectivity
Na+
K+
Ca2+
serotonin ion selectivity
Na+
K+
ION CHANNEL-ENCLOSING RECEPTORS
IP3, cGMP, cAMP, ATP
- receptors
- amplification system
- acceptors
- biological response
- on IC membranes
- channel-transmitted ions
- myosin, membrane ion channels
- muscle contraction, depolarisation, hyperpolarisation, activating of energy producing metabolic pathways also
IP3 ion selectivity
Ca2+
cGMP ion selectivity
Na+
K+
cAMP ion selectivity
Na+
K+
ATP ion selectivity
K+
overview of signalling system of ion channel-enclosing receptors
example of signalling via 7-transmembrane domain receptors
β adrenergic receptors
structure of 7 transmembrane domain receptors
amino terminal lies on EC side
carboxyl-terminal is in the cytosol
ligand sits in a pocket formed by transmembrane helices
upon R activation, the R binds a G protein (GPCRs)
3rd TM domain recognises the G protein
amplification system of G-protein activated adenylate cyclase
how does protein kinase A regulate the acceptor
PKA when activated by cAMP can penetrate the nuclear membrane
It can then phosphorylate CREB
When phosphorylated, it is ACTIVE and helps to initiate gene expression