Question

Answer the following questions regarding to the second step of Citric acid cycle (isomerization of citrate to isocitrate)

1. how does the second step of CAC fits into the larger metabolic pathway? overall outcome?

2. enzymes involved. Also categorize the type of the enzyme. explain!

3. Thermodynamics? endergonic or exergonic? if any differences between standard state and actual free energy.

4. regulations?

Answer 1

CITRIC ACD CYCLE

In citirc acid cycle/ kerbs cycle/ tricarboxylic acid cycle, what actually happens s the oxidation of the fuel molecules (glucose derivatives, carbohydrates, fatty acids) into the carbon dioxide and thus obtained electrons are transported to the electron transport chain for reducing oxygen during generating ATP.

1. In the 1 st step the condensation of acetyl CoA with oxaloacetate to form citrate by the citrate synthase enzyme.

n the 2nd step isomerization of citrate to isocitrate takes place. the citrate contains a tertiary alcohol group. the tertiary alcohol group cannot be attacked for oxidation if no breaking of a carbon bond. but through a rearrangement, the tertiary alcohol can be converted into secondary alcohol (in isocitrate)

for ths the OH group is transferred from the 1 st carbon atom to the 2 nd carbon atom by changing the location of the water molecule. The interchanging of H and OH molecules re interchangeable wth the enzyme here ACONTASE.

2. The enzyme here n second step involved is the ACONITASE. the ACONITASE enzyme is considered as an iron-sulfur protein.it is not considered as an isomerase. but it is a lyase enzyme. this is because during each step of the reaction the substrate molecules are released.

3.endergonc reaction: higher free energy for product molecules than the reactants.

Exergonic reaction: higher free energy for the reactants than product molecules.

From citrate to isocitrate the reaction is Endergonic reaction because free energy for isocitrate is higher than citrate molecules.

From citrate to isocitrate-

=6.4KJ/MOL.

That is free energy s positive.if another reaction consumed faster the isocitrate as it made then the value is always positive.

4. The amount of reactants(citrate) if decreases then a regulation can happen always for every reaction.

Also regulation in the enzyme aconitase can also regulate the isocitrate synthesis