Energy Production: Carbohydrate 3 Flashcards
What is an important factor used in regulation of metabolic pathways?
Allosteric regulation of enzymes. An activator or inhibitor binds at another site than the active site.
Also covalent modification can be used. This is phosphorylation or dephosphorylation where there is an introduction of a bulky negatively charged PO42- moiety which alters the protein conformation and therefore the activity.
In which steps of the pathways of metabolism are allosteric regulators and covalent modifiers used? Why not somewhere else?
On the irreversible steps. In glycolysis this would be step 1, 3 and 10. This reduce the levels of product.
Why they are not used on reversible steps is that even when they are inhibited the reactions still come to equilibrium so levels of product will be unaffected.
Which step is the most favourable step to inhibit the pathway?
On the first step. Usually we don’t want intermediates to build up because they get ‘stuck’.
Why would enzyme inhibition on a reversible step not be of very much use?
Because enzymes do not affect the equilibrium of a reaction, it affects the rate. This means that even though the product would be produced slower, it would be produced in the same amount still.
Explain product inhibition.
Say you have a 5 intermediates in a reaction. Intermediate 3 product starts to build up in the pathway. This is also a reversible step. The increase in the concentration of intermediate 3 shifts the equilibrium to intermediate 2 instead. This reduces the binding rate of intermediate 2 and reduces the catalysis of intermediate 2 to 3.
Where are you most likely to see product inhibition?
Most favourably intermediate 5 or the final product rather will inhibit the first intermediate or the first substrate rather.
What is feedback inhibition?
It’s very similar to product inhibition or even the same? Where the final product inhibits the chain reaction to start again.
Why would inhibition at the committing step be favourable?
Because this means that a substrate can go into other pathways.
Give examples of what catabolic pathways can be inhibited by.
High energy signals such as ATP, NADH and FADH2.
Give examples of what catabolic pathways can be activated by.
Low energy signals such as ADP, AMP, NAD+ and FAD+.
Explain how hormonal regulation can work.
A hormone binds to a receptor. It activates a signalling pathway which then activates protein kinase to cause phosphorylation (covalent modification) or a protein phosphatase to cause dephosphorylation.
Phosphorylation or dephosphorylation either activates or inhibits an enzyme.
Give examples of phosphoregulation.
Adrenaline and insulin
Explain how adrenaline phosphoregulate.
Activates protein kinase A (PKA) which then activates phosphorylase kinase which then phosphorylates glycogen phosphorylase.
In short this stimulates glycogen breakdown.
Explain how insulin phosphoregulate.
Either stimulate glucose utilisation or inhibits glycogen breakdown.
Where in glycolysis would you most likely see regulation of the pathway?
In the committing step aka step 3.
