Explain what it means for the activation energy to be lowered from 18 to 13 kcal

Question

Explain what it means for the activation energy to be lowered from 18 to 13 kcal/mol by ferric ions but from 18 to 7 Kcal/mol by catalase. Select all that apply As shown in the reaction below, hydrogen peroxide, H2 02, decomposes to H2O and O2 The activation energy, EA for the uncatalyzed reaction at 20 °C is 18 kcal/mol. The reaction can be catalyzed either by ferric ions (E-13 kcal/mol) or by the enzyme catalase (EA 7 kcal/mol). Part A Part B Explain what it means for the activation energy to be lowered from 18 to 13 kcal/mol by ferric ions but from 18 to 7 kcal/mol by catalase. Select all that apply. Catalase provides a surface that is more conducive to reaction then ferric ions Catalase provides a surface that is less conducive to reaction then ferric ions Ferric ions have a surface on which the molecules are positioned such that their reaction is more favorable than when the molecules are present in solution Ferric ions have a surface on which the molecules are positioned such that their reaction is less favorable than when the molecules are present in solution Submit Request Answer Part C Choose two properties of catalase that make it a more suitable intracellular catalyst than ferric ions. Select all that apply. O The active site of the enzyme favors maximally the decomposition of H2 02 molecules. O The enzyme is insensitive to temperature changes The active site of the enzyme provides a surface that is very specific for the binding of H202 decomposition products: H2O and O2 O The active site of the enzyme provides a surface that is very specific for the binding of H2 02 molecules. Submit

Explanation / Answer

Lowering down the activation energy from 18 to 7 means catalase enzyme favors the decomposition of H2O2 in better ways than Fe ion, which is indicated by activation energy values. For a reaction to occur with fe ions as catalyst the reactants requires higher energy to cross the reaction energy barrier whilw it is lowered down with the help of catalase enzyme by providing specific conformations and space for the reaction to occur.

Part B

Catalase provides the surface which is more conducive to reaction then feric ions.

For an enzyme to work, it must have a highly specific active site or pocket in which the substrate can fit. Beside this, for decomposition of H2O2, one proton of H2O2 must be removed from one end of mole and to be tranferrd to the other end which is done by a histidine residue in the active site of enzyme after binding of H2O2 to heam group and oxidising it to Fe(IV). This results into breakage of O-O bond and release of water molecule.

So the whole reaction has been facilitated by active site of enzyme by providing a surface for required components to interact. This is actvation energy is lowered down by the enzymes.

Part C

The active site of the enzyme maximally favors the decomposition of H2O2 and The active site of the enzyme provides a surface which is very specific for the binding of the H2O2 molecules.

The active sites of enzymes are very specific for the substrates and these sited energetically favor the binding of the substrate.

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