Metabolism - Lec 4 Flashcards
what is allostery?
activation or inhibition of an enzyme by binding at the regulatory site
it affects catalytic activity
an example is covalent modification such as de/phosphorylation.
what is this ?
de/phosphorylation
introducing the bulky negative PO4 2-
this can alter protein strucutre and hence activity
what are the principles of metabolic pathway regulation?
Irreversible steps are possible points of regulation
reducing activity - reduces flux of substrates through pathway - reduces products
reversible steps are not regulated, reactions will always come to equilibrium - product levels are unaffected
how does product inhibition work ?
if pathway intermediates build up, they will sit at equilibrium and flux through pathway slows - this is inefficient
overall result is a reduced rate of catalysis
most common biological solution to this is to inhibit the first step of the pathway, reduces substrate entry and intermediate build up. this is called FEEDBACK INHIBITION
the trigger for this is high concentrations of product
what is the committing step?
it is a step, that can be inhibited, that would commit the substrate to this path.
if inhibited we can divert substrate into other pathways
how is the catabolic pathway regulated?
it is inhibited by high energy signals - ATP NADH FADH2 - Body says lots of energy atm, stop making more - divert to storage
its activated by low energy signals - ADP, NAD+,FAD -
body says low energy need to make more - bring stuff out of storage
Outline hormone regulation
hormones bind to a receptor to activate a signalling pathway
Protein kinases will phosphorylate or protein phospahte will dephosphorylate the target enzyme
altering activity
what is feed forward?
early pathway substrate provides positive allosteric signal
activates a enzyme later in the pathway
an example of this is fructose 2,6 Bisphosphate
give two examples of phosphoregulation
- Adrenaline - activates protein kinase A
Phosphorylation activates Phosphorylase kinase
Phosphorylation of Glycogen Phosphorylase - stimulates glycogen breakdown
a multi step respone - Insulin - stimulated signalling pathway actiavtes protein phosphotase 1
desphosphorylates and activates pyruvate dehydrogenase - stimulating glucose ultilisaiton
dephosphorylates glycogen phosphotase - inhibiting glycogen breakdown
Key Point : phosphorylation and dephosphroylation may be stimulatory or inhbitory depending on the target enzyme
What is the key regulator of glycolysis ?
phosphofructokinase 1
how does phosphofructokinase 1 (PFK) work ?
converts Fructose 6 phosphate to fructose 1,6- bisphosphate - this provides a energtically unstable molecule to break into two c3 molecules
uses an ATP to ADP - energy used
how is PFK regulated ?
Allosteric regulation (Muscle) -
- Inhibited by high ATP
- Stimulated by high AMP
Hormonal regulation (Liver) -
- Stimulated by Insulin
- Inhibited by Glucagon
Fructose 2,6 bisphosphate production from Fructose 6 phosphate also stimulates PFK 1
it is fructose FEED FORWARD encouraging fructose metabolsim
there are other inhibitors such as H+ ions, Citrate from TCA cycle and PEP (extra)
What are other regulation mechanisms in glycolysis ?
may be best to draw the pathway in full if you can
Hexokinase - 1st step phosphorylation uses ATP
inhibted by Glucose 6 phosphate - G-6-P - a intermediary later in pathway
High NADH, Low NAD+
Hormonal Activation - PFK and Pyruvate kinase
high amounts of insulin to glucagon ratio will lead to this activation of pathway
consider and explain product inhibition by NADH
High NADH or low NAD+ is a high energy signal
causes a product inhibtion of step 6
inhibiting glycolyisis
substrates feed out into storage pathways
How is PKF phosphoregulated ?
pyruvate kinase is the same
insulin signals to Protein phosophotase 1 which removes P and stimulates PKF-1
Glucagon signals to protein kinase A (PKA) - adds P - inhibits PKF-1
