Lecture Two - intracellular signal transduction pathways Flashcards
what is a signalling pathway? give the definition
binding of a ligand to a receptor initiates a signal transduction pathway
intracellular signal transduction pathways process information.
what information is given to a cell to ilicit a response? a
environmental stresses
signals from other cells
extracellular matrix
nutrient signals
internal states - homeostasis, cell cycle
what biological outputs occur due to information given to a cell?
gene expression
morphological changes
production/secretion
growth/division
senescense/death
what is core concept one in intracellular signalling?
environmental changes (internal or external) must be sensed by the cell
via the activation of cell surface receptors and intracellular nuclear receptors
what is core concept two in intracellular signalling?
cells respond to these environmental changes by activating or inhibiting the activity of specific intracellular signalling pathways to change their biological function/fate
by conformational changes in intracellular signalling molecules, changes in protein structure (post-translational modification), and generation of second messengers
what is an example of conformational changes in intracellular signalling molecules?
heterotrimeric G-protein complexes
* non-active GPCR - G⍺ subunit is bound to GDP is complexed with Gβ𝛾 subunits and is inactive
ligand-bound GPCR - G⍺ subunit releases GDP and binds GTP, this changes its conformation causing the Gβ𝛾 subunbit to dissociate, both of the free G⍺ and Gβ𝛾 subunits are now active
receptor dimerisation and activation (enzyme coupled receptors)
* binding of a signal molecule in form of a dimer activates the catalytic domain
* binding of a signal molecule activates an associated enzyme
what is the result of a change in protein structure (post-translational modification)?
can lead to changes in protein-protein interactions e.g. phosphorylation
can lead to changes in protein expression by triggering protein degradation e.g. ubiquitylation
what is eukaryotic cell division initiated by?
mitogens and growth factors that act to satisfy the restriction checkpoint (R)
PDGF binds to its cell surface receptor resulting in signal transmission, and transcriptional response, resulting in cell growth and cell division, by regulating the entry of cells into the cell cycle and progression to the restriction point.
what regulates the restriction checkpoint?
G1 phase CDK’s and cyclins
what is a cyclin?
regulatory subunit
expression levels controlled by rates of protein synthesis vs protein degradation.
G1 phase cyclin = cyclin D
what is CDK?
catalytic subunit
protein kinase activity controlled by cyclin binding and protein phosphorylation
G1 phase CDK’s = CDK4 & CDK6
where are M-phase cyclins degraded?
at the spindle assembly point (SAC) by the APC/C ubiquitin lipase to promote chromosome segregation in anaphase
what does PDGF stand for?
platelet-derived growth factor
what does CDK stand for?
cyclin-dependent kinase
what are examples of second messengers?
AC - adenylyl cyclase
PLC - phospholipase C
give the process catalysed by adenylyl cyclase.
ATP produces cAMP using adenylyl cyclase as a catalyst releasing a pyrophosphate molecule
cAMP is only produced in response to GPCR activation
what activates the β isoform of phospholipase C?
G⍺q downstream of GPCR’s
what activates the 𝛾 isoform of phospholipase C?
kinase-linked receptors
what is the equation of the reaction that phospholipase C catalyses?
PI 4,5 -bisphosphate [PI(4,5)P2]
> diacylglycerol > activates protein kinase C
> IP3 > releases Ca2+ from the endoplasmic reticulum
what does IP3 stand for?
inositol1,4,5-triphosphate
what is the process of the PKA signalling pathway?
binding of 4 cAMP molecules to an R2C2 complex induces a conformational change of the regulatory subunits to release the two catalytic subunits which are then free to phosphorylate proteins in the cytoplasm
give examples of the proteins phosphorylated by active protein kinase A
- several Ca2+ handling proteins are phosphorylated by active PKA catalytic subunits > muscle contraction/relaxation
- PKA regulates the activity of several metabolic enzymes > release of glucose from glycogen
- PKA regulates the transcription of specific genes e.g. active PKA catalytic subunits travel into the nucleus and activate CREB by phosphorylation. active CREB activated CBP at the CRE which results in gene transcription of the target gene.
what does PKA stand for?
protein kinase A
what does CREB stand for?
cAMP-response element binding protein
what does CBP stand for?
CREB-binding protein
what does CRE stand for?
cAMP response element
what is core concept three in intracellular signalling?
cells can organise intracellular signalling pathways efficiently in 3D space to allow them to rapidly respond to environmental changes
* components of an intracellular signalling pathway can be preassembled into an efficient signalling complex within a small 3D area - organised by a large scaffold protein
what is core concept four in intracellular signalling?
the activity of intracellular signalling pathways can be amplified to filter out random fluctuations (‘noise’) and ensure the biological fate of a cell is not altered by chance
how is the activity of a signalling pathway amplified?
- increase the amount of ligand available to a cell
- increase the number of available receptors expressed by a cell
- make use of enzymes
- use positive feedback loops
what is core concept five in intracellular signalling?
positive and negative feedback pathways can alter the activity of intracellular signalling pathways
* in positive feedback, the output stimulates its own production
* in negative feedback, the output inhbits its own production
* can be used to alter the amplitude, duration and reversibility of a responsew
give an example of positive feedback?
can enhance intracellular calcium signalling
can enhance the activity of M-phase cyclin/CDK complexes at the G2/M checkpoint
what is core concept six in intracellular signalling?
a single ligand can induce different biological outcomes in different cells
* ligand (first messenger) > receptor > membrane-associated effector > second messenger > first intracellular target > biological outcome
give an example of core concept six.
adrenaline/noradrenaline on different types of smooth muscle…
bronchi = broncho-dilation
blood vessels = vasoconstriction
what is core concept seven in intracellular signalling?
a single receptor/ligand pair can activate more than one intracellular signalling pathway
