Lesson 7: Bioenergetics and Redox

Homolytic cleavage

Bond breaks evenly; each atom gets one electron.

Heterolytic cleavage

Bond breaks unevenly; one atom gets both electrons.

Nucleophile

Electron-rich species that donates an electron pair.

Electrophile

Electron-poor species that accepts an electron pair.

Aldol condensation

Joins carbonyl compounds and forms a C–C bond.

Claisen condensation

Joins esters to form a β-keto ester.

Elimination reaction

Removes groups to form a double bond.

Isomerization

Rearranges atoms to form a different isomer.

Group transfer reaction

Transfers a functional group from one molecule to another.

Kinase

Transfers a phosphoryl group, usually from ATP.

Phosphoryl group transfer

Moves a PO₃²⁻ group between molecules.

Phosphorylase

Adds phosphate using inorganic phosphate (Pi).

Phosphatase

Removes a phosphate group by hydrolysis.

Synthase

Catalyzes synthesis without directly using ATP.

Synthetase

Catalyzes synthesis using ATP energy.

Ligase

Joins molecules, usually using ATP energy.

Lyase

Breaks or forms bonds without hydrolysis or oxidation.

Dehydrogenase

Catalyzes oxidation-reduction by transferring hydrogen/electrons.

Oxidation-reduction reaction

A reaction involving transfer of electrons.

ATP hydrolysis free energy

ATP hydrolysis has a large, negative ΔG under cellular conditions.

Mg²⁺ and ATP

Mg²⁺ binds ATP and helps stabilize its negative charges.

High-energy phosphate compound

Compound whose hydrolysis has a large, negative ΔG.

Phosphoenolpyruvate hydrolysis

Has very large negative ΔG because products are strongly stabilized.

1,3-Bisphosphoglycerate hydrolysis

Releases substantial free energy due to product stabilization.

Phosphocreatine hydrolysis

Releases more free energy than ATP hydrolysis.

Acetyl-CoA hydrolysis

Thioester hydrolysis releases substantial free energy.

Thioester

Compound containing a sulfur-linked acyl group; hydrolysis is favorable.

Thioester vs oxygen ester hydrolysis

Thioesters generally have more negative hydrolysis ΔG than oxygen esters.

ATP energy

first step

ATP energy

second step

ATP energy mechanism

ATP usually provides energy through group transfer, not simple hydrolysis.

High-energy phosphate ranking

PEP > 1,3-BPG > phosphocreatine > ATP > lower-energy phosphates.

High-energy vs low-energy phosphates

High-energy compounds have more negative hydrolysis ΔG than ATP; low-energy have less negative ΔG.