Final answer:
NAD and NADPH differ in the presence of an extra phosphate group on the ribose sugar in NADPH, which is involved in metabolic processes and photosynthesis.
Step-by-step explanation:
NAD and NADPH are distinguished from each other by the phosphate group that's bonded to the sugar ring attached to the adenine. The molecule Nicotinamide adenine dinucleotide (NAD+) is a coenzyme that exists in two forms: NAD+, which is the oxidized form, and NADH, the reduced form. The difference between NAD+ and its phosphorylated counterpart, Nicotinamide adenine dinucleotide phosphate (NADP+), lies in the presence of an extra phosphate group attached to the ribose sugar in the latter. This additional phosphate group is what differentiates NADPH from NADH. The molecules, both being derived from niacin (vitamin B3), play critical roles in metabolic processes, with NAD+ being central to energy production and NADP+ being important in anabolic reactions and photosynthesis.