lecture 3 Flashcards
Rate of reaction depends on?
Conc of substrates
Rates are more sensitive to conc at cones near or below their kM
Rate is insensitive as enzyme becomes saturated
If livers km is the highest for glucose , what does this mean
More able to respond to increases in glucose than any other tissue
In fed state, liver and pancreas are able to take up glucose more quickly than other tissues §
Endocrine system features
Used alongside nervous system to control organ systems and maintain homeostasis
Uses hormones in bood stream
How are the endocrine and nervous system connected
Directly via the hypothalamus and pituitary gland
Signal transduction
Converting one type of signal to anotherS
Neuronal signalling
Action potentials transmitted along axon
When signal reaches nerve terminal, causes release of neurotransmitters onto adjacent cells
Contact dependent signalling
Cell surface bound molecule binds to a protein receptor on an adjacent cell
No molecules released
paracrine signalling
released by cells into extracellular fluid in their neighbourhood as local mediators
Endocrine signalling
Secreted into the blood stream and distributed WIDELY
Cell surface receptors
Most extracellular signal molecules are large and hydrophilic - can’t cross membrane
Generate intracellular second messagner signalling molecules
Intracellular receptors
Some small hydrophobic extracellular molecules pass through membrane and bind to intracellular receptors that regulate eg gene transcription
How does AcH effect heart peacemaker cell, salivary gland cell and skeletal muscle cell
Heart = decreased rate of firing Salivary = secretion Skeletal = contraction
Processes that rely on altered protein function - eg movement secretion and metabolism are ..
fast
Processes that rely on altered protein synthesis e.g. differentiation, growth and division are …
slow
explain the pathway from extracellular signalling molecule
Signalling molecule receptor protein Intracellular signalling molecules Effector proteins Target cell responses
3 main types of cell surface receptor
Ion channel coupled receptors
G protein coupled receptors
Enzyme coupled receptors
Ion channel coupled receptors
Transmission of signals across synapses
Neurotrasnmitter signal molecules
Opening of receptors causes chance in electrical potential across membrane
G protein coupled receptors
Extracellular portion binds a signalling molecule
Cytoplasmic portion binds a G protein
Adenylyl cyclase
Catalyses the formation of the second messenger cyclic AMP ( cAMP)
Phosholipase C
Produces the second messengers IP3 and DAG
Ip3 promotes accumulation of cytosolic Ca2+ ( another secondary messenger)
Effect of adrenaline on skeletal muscle
Adrenaline activates a GPCR, which activates a G protein that activates adenylyl cyclase = increasing cAMP
cAMP activates protein kinase A that phosphorylates phosphorylase kinase
phosphorylase kinase activates glycogen phosphorylase ( breaks down glycogen)
How does cholera effect GPCR
Modifies the a subunit of G protein for cAMP
Stops G protein deactivating, so it contuinely activates adenyl cyclase
Increased cAMP causes continual outflow of Cl- ions dn h2o
