Two important electron carrier molecules that are used in cell metabolism are- nicotinamide adenine dinucleotide (NAD+)
- flavine adenine dinucleotide (FAD)
- nicotinamide adenine dinucleotide phosphate (NADP+)
For example, when synthesizing ATP, NAD+ carries electrons of a hydrogen
(H) atom, making NADH. FAD carries two electrons of hydrogen making
FADH 2. Very often electrons of hydrogen atoms are the electrons transported by
the carrier molecule. NADP+ is used to reduce CO 2 to carbohydrates during the
Dark Phaseof photosynthesis.
Making Power: ATP Production
When enzymes break down nutrients (larger molecules) into smaller molecules,
the energy that is released can be stored and used for future anabolic reactions.
Here are the steps to form ATP:
1.Substrate-level phosphorylation: Phosphate is transferred from another
phosphorylated organic compound to ADP to make ATP during an exer-
gonic reaction.
2.Oxidative phosphorylation: Energy from redox reactions of biochemical
respiration is used to attach an inorganic phosphate to ADP to make ATP.
3.Photophosphorylation: Energy from sunlight is used to phosphorylate ADP
with inorganic phosphate.What’s Your Name:
Naming and Classifying Enzymes
Enzymes are named according to the substrate that they act upon, and most end
in the suffix “-ase.” Enzymes are classified into six major groups based on their
actions. These classifications are:
- Hydrolases: Enzymes in the hydrolasesgroup increase a catabolic reaction
by introducing water into the reaction. This reaction is called hydrolysis.
For example, lipase(lipid + ase) is an enzyme that is used to break down
lipid molecules.
CHAPTER 5 The Chemical Metabolism^89