Metabolism Flashcards
What is an exergonic reaction?
Reaction where ΔG∘’
What is an endergonic reaction?
Reaction where ΔG∘’ > 0
Why is the process of coupling a reaction?
For a reaction to be feasible, only overall ΔG∘’ needs to be -ve. This means that a reaction with +ve ΔG∘’ can be coupled with much more -ve ΔG∘’ reactions in order to make them feasible, since overall ΔG∘’ would be -ve.
What is a ‘state function’?
A function that will be the same no matter what pathway is taken, so long as the initial and final states are the same.
What are the associated ΔG∘’ values for hydrolysis of ATP?
ATP + H2O → ADP + Pi (-30.5 KJ mol^-1)
ATP + H2O → AMP + PPi (-45.6 KJ mol^-1)
PPi + H2O → 2Pi (-19.2 KJ mol^-1)
Why is ATP the universal energy currency?
- ATP hydrolysis is exothermic and is coupled with the majority of endothermic metabolic reactions in order to make them feasible.
- ATP synthesis is endothermic and is coupled with the majority of exothermic metabolic reaction. It acts as an energy carrier between endothermic and exothermic reactions.
Why is ATP hydrolysis so exothermic?
- ADP and Pi have more resonance stabilisation, so are more stable and in a lower energy state than ATP.
- There is more electrostatic repulsion between phosphate groups in ATP compared to ADP and Pi.
- More water is able to bind to ADP and Pi in order to stabilise them by hydration.
What is the implication of a very -ve ΔG∘’ on K?
A very -ve ΔG∘’ indicates a very large K, so position of equilibrium lies far to the right in favour of product formation.
What is the implication of a very +ve ΔG∘’ on K?
A very +ve ΔG∘’ indicates a very small K, so position of equilibrium lies far to the left in favour of reactants.
What is the phosphorylation potential?
The ΔG∘’ that occurs when a phosphorylated compound is dephosphorylated by hydrolysis.
What is the significance of the phosphorylation potential?
A compound with a more -ve phosphorylation potential is capable of phosphorylating a compound with a less -ve phosphorylation potential.
Why does ATP not have a very -ve phosphorylation potential?
- In order to ensure that energy is released in small packets as not to damage cells.
- In order to ensure that it can be phosphorylated relatively easily by other biological compounds (eg phosphocreatinine).
What is the benefit of having 2 separate redox systems for energy production and biosynthesis?
- NAD+/NADH used for energy production.
- NADP+/NADPH used for biosynthesis.
- Allows for the 2 processes to be uncoupled from each other.
- NAD+/NADH ratio kept high for oxidation in energy production.
- NADPH/NADP+ levels kept high for reduction in biosynthesis.
What is the role of the liver in fuel metabolism?
- Glucose homeostasis
- Synthesis and storage of triglycerides
- Oxidation of fats and synthesis of ketone bodies
- Nitrogen recycling and amino acid metabolism
What are the heart’s preferred fuels?
- Fats
- Ketone bodies
Why does enzyme activity need to be regulated?
- To avoid futile cycles.
- To link energy production to usage.
- To respond to physiological changes in the body (e.g. fasting, exercise).
- To prevent the build-up of intermediates that take part in side-reactions (feedback inhibition).
What are the physiological states that affect metabolism?
- Fasting/feasting
- Short-term exercise
- Long-term exercise
- Diabetes mellitus
What are the main functions of glycolysis?
- Substrate-level phosphorylation of ADP to ATP allows some ATP to be produced in glycolysis, which is especially important in anaerobic respiration when oxidative phosphorylation in aerobic respiration cannot keep up with ATP demand.
- NADH produced enter the mitochondria and are reoxidised, releasing energy used in oxidative phosphorylation.
- Produces pyruvate which is further broken down in the citric acid cycle.
What is the overall purpose of steps 1-4 of glycolysis?
Lysis stage. 2 ATP molecules are consumed in order to split the glucose molecule into GAP and DHAP
What is the purpose of isomerisation of G6P into F6P?
In step 4, the mechanism of cleavage for F1,6BP is aldol cleavage, which requires ketone group at C2, hence the isomerisation.
What is the overall purpose of steps 5-7 in glycolysis?
Oxidation stage. Aldehyde groups in GAP are converted to carboxyl groups that are more stable. The energy released from this process is subsequently used to phosphorylate 2 molecules of ADP per GAP.
Why is triose phosphate isomerase (TIM) considered a ‘perfect enzyme’?
- Its rate of catalysis is almost instantaneous once all the substrates have bond.
- Increasing the catalytic efficiency of the enzyme has no effect on rate of reaction.
- Rate of reaction only limited by the rate at which the substrate-enzyme complex forms.
What is the overall purpose of steps 8-10 in glycolysis?
Rearrangement stage. C=C and C=O bond in PEP are converted to 2 C=O bonds that are more stable. The energy released from this reaction is used to phosphorylate another ADP to ATP.
What is the overall reaction of glycolysis?
Glucose + 2 ADP + 2Pi + 2 NAD+ → 2 Pyruvate + 2 NADH + 2H+ + 2ATP + 2H2O