Biosignalling Flashcards
What do extracellular signalling molecules bind to in the cell surface membrane?
protein receptors
What happens when extracellular signalling molecules bind to protein receptors in the cell surface membrane?
a cascade of reactions inside the cell is triggered
What are protein receptors in the cell membrane specific to?
extracellular signalling molecules
How can a large intracellular response be created from a single protein receptor?
cascades can amplify the signal they receive, very few molecules can lead to a large intracellular response
What must cells be able to do once the signal concentration falls?
switch off the response
what are the 4 types of inter cellular signalling?
endocrine, paracrine, neuronal, contact dependent
How does endocrine inter cellular signalling work?
the signalling molecules from one cell/tissue travel to other cells/tissues via the blood stream
How does pancrine intercellular signalling work?
signalling molecules from one cell act on the cells in the immediate surrounding area
How does neuronal intercellular signalling work?
signalling molecules are released from the end plate of a neuronal cell and travel across a synapse to the receptors on the target cell
How does contact dependent intercellular signalling work?
siganlling molecules are expressed on the cell surface of one cell and bind to the receptors of another cell when the two come into contact
What is the cell response the sum of?
all the signals it receives
What else determines a cells response aside from the signal strength?
the cell type
Do different cells have the same/similar receptors for the same signal molecules?
yes
What differs between cell types in terms of their response to signaling?
they have different intracellular cascades with different effector proteins
How do different intracellular cascades and effector proteins affect the cells response to signal proteins?
they can have different responses to the signal protein
How does acetylcholine affect heart muscle cells, salivary gland cells and skeletal muscle cells when it binds to the receptor molecule?
heart muscle cell: decreased rate and force of contraction
salivary gland cell: secretion of saliva
Skeletal muscle cell: contraction
What are the two speeds of cell response to signal proteins?
fast or slow
What do fast cell responses involve?
altering protein function within the cell
What does altered protein function within the cell after fast response to signal proteins lead to?
altered cytoplasmic behavior and altered cell response
How quickly does a fast cell response happen?
within milliseconds to a few minutes of receiving the signalling molecule
What do slow cell responses involve?
altering gene expression leading to the increase/decrease of protein synthesis or synthesising new proteins
how is gene expression altered by signalling proteins?
increasing or changing the signals to the DNA for protein synthesis
How does the change in amount or type of proteins synthesized affect the cell?
alters cytoplasmic behavior and alters cell response
how quickly does a slow cell response to signal molecules happen?
minutes to hours
Where can receptors be located?
on the cell surface membrane or intracellular
What type of signalling molecules do intracellular receptors require?
hydrophillic ones that can enter the cell
What receptors can hydrophobic signalling molecules bind to?
only cell surface receptors
What are the 3 types of cell surface receptors?
ion-channel coupled receptors, G protein couple receptors (GPCRs), enzyme coupled receptors
Give 2 examples of electronically excitable cells
muscle and nervous system cells
In what type of cells are ion-channel coupled receptors located?
electrically excitable cells
What do cell surface receptors in electrically excitable cells convert?
chemical signals to electrical ones
What happens when the signalling molecule binds to the ion channel?
it opens allowing ions across the plasma membrane
What are ions?
charged molecules (eg Cl-, K+)
What does the movement of ions across the plasma membrane do to the membrane?
changes membrane potential of the cell and produces and electric current
What body function are ion-channel coupled receptors responsible for?
rapid transmission of signals across synapses in the nervous system
What are G proteins?
a class of proteins that sit in the plasma membrane and amplify the signal from receptor molecules
What are G proteins linked to?
cell surface receptors
What do the cell surface receptors linked to G proteins do when activated by a signalling molecule?
activate G proteins
What do G proteins do once activated by linked cell surface receptors?
activate many enzyme molecules, amplifying the signal by producing large quantities of secondary messenger molecules
Give and example of where GPCR is used?
adrenaline moved through GPCR to stimulate glycogen breakdown in skeletal muscle
What does adrenaline bind to when using GPCR?
beta adrenergic GPCR in the plasma membrane
What subunit of the G protein activates adenyl cyclase?
alpha subunit
What is adenyl cyclase?
an enzyme that produces cyclic AMP (cAMP) from ATP
What does cyclic AMP activate during the GPCR response?
cAMP dependant protein kinase (PKA)
What does PKA activate, once it has been activated by cyclic AMP, and how does it activate it?
phosphorylase kinase by adding a phosphate group to it from ATP
What does active phosphorylase kinase activate and how does it do this?
glycogen phosphorylase by adding a phosphate group to it from ATP (phosphorylation)
What does the activated glycogen phosphorylase catalyse at the end of the GPCR cascade?
glycogen breakdown
What are receptor tyrosine kinases (RTKs)?
a large family of cell surface receptors that have intrinsic protein kinase activity
What does the binding of a signalling molecule to RTKs induce?
formation of a dimer from receptors (joined molecules) which then activates intracellular proteins (protein kinase)
What does the activation of the intracellular protein kinase domain do?
phosphorylates both the receptor (autophosphorylation) and other target proteins that are on the tyrosine residues
Once the phosphorylation of receptors and target proteins has occurred in the RTK signalling response what happens to the signal?
it is relayed by activated signalling proteins in the cells interior
What are examples of RTK receptors?
insulin receptors and epidermal growth factor receptors
What are secondary receptors?
intracellular receptors that bind to molecules released by cell surface receptors
What are the molecules that can often enter cells?
hormones
What binds to intracellular signalling receptors?
signalling molecules that enter the cell
How is a hormone typically carried to tissues?
via a serum binding protein which diffuses across the cell membrane
Once in the cell what does the hormone bind to?
intracellular receptor in the cell nucleus
What does the binding of the hormone to the intracellular receptor in the cell nucleus cause?
dimerization with other hormone receptor complexes
What are specific regulatory regions in the DNA called?
hormone response elements (HREs)
What are HREs adjacent to?
specific genes
What does the dimerised intracellular hormone receptor attract?
coactivator/compressor protein(s) that regulate the transcription of the adjacent gene
What does the increased/decreased mRNA production, as a result of coactivator/conmpressor proteins, alter?
the production of the corresponding protein which produces a cellular response
