Enzyme-mediated Biochemical Reactions

Identify the six (6) enzyme-mediated biochemical reactions.

1. Group-transfer reactions

2. Formation/removal of carbon-X bonds

3. Isomerization reactions

4. Ligation reactions

5. Hydrolysis and dehydration synthesis reactions

6. Oxidation-reduction reactions

Explain group transfer reactions.

Group-transfer reactions are mechanisms that transfer a functional group from one molecule (donor) to another (acceptor).

Explain the formation/removal of carbon-X bonds.

This mechanism is a lyase-mediated synthesis/cleavage pathway that does not involve hydrolysis or oxidation. These reactions run in two (2) distinct directions:

(1) Forward reaction pathway (cleavage)

• In this mechanism, lyase cleaves a single bond across a molecule.

• This yields two distinct molecules with a new double bond, respectively, at the cleavage site.

(2) Reverse reaction pathway (synthesis)

• In this mechanism, lyase adds a functional group across a double bond.

• In the reverse reaction, lyase might be referred to as “synthase” instead.

In a lyase-mediated reaction pathway, the forward and reverse reactions occur simultaneously. The dominant directionality is determined by where the reaction is situated at equilibrium, which is determined by the overall free energy (ΔG).

Explain isomerization reactions.

Isomerization reactions occur when a molecule undergoes structural rearrangement to produce an isomer: a class of molecules that share the same molecular formula.

Explain ligation reactions.

Ligation reactions are ATP-mediated synthesis pathway that joins two (2) molecules together.

Explain hydrolysis reactions.

Principally, hydrolysis is a catabolic mechanism that involves the addition of water to break down polymers into their monomeric constituents.

More specifically, hydrolysis involves a nucleophilic reaction between a functional group center and water:

• Electrophile: Phosphate or carboxylic acid (δ+ center)

• Nucleophile: Water’s oxygen (δ-)

The leaving group of hydrolysis reactions will end up being an alcohol or an amine.

Explain dehydration synthesis.

Principally, dehydration synthesis (condensation) is an anabolic pathway that involves the removal of water to join monomers into a larger polymer structure.

More specifically, dehydration synthesis involves a nucleophilic reaction between the partial charges of two (2) functional groups:

• Electrophile: Phosphate or carboxylic acid (δ+ center)

• Nucleophile: Alcohol or amine (δ-)

The leaving group will always end up being water.

What broad mechanistic category do hydrolysis and dehydration synthesis reactions fall into?

Both reactions are a crucial component of macromolecule catabolism and anabolism.

Both mechanistic pathways involve a nucleophilic reaction that takes place at a partially-positive, electrophilic functional group center. The nucleophile is a partially-negative molecule (i.e., water, alcohol, or amine).

Explain oxidation-reduction reactions.

Oxidation-reduction reactions involve the transfer of electrons between two (2) reacting molecules.

• Oxidation = loss of electrons = net-positive charge

• Reduction = gain of electrons = net-negative charge