Reducing equivalents in fatty acid synthesis are supplied by
Ans. b (NADPH + H+) (Ref. Harper's, Illustrated, 27th/ 87-88, 176)DEHYDROGENASES# Dehydrogenases cause the transfer of hydrogen from one substrate to another in a coupled oxidation-reduction reaction.# These dehydrogenases are specific for their substrates but often utilize common coenzymes or hydrogen carriers, eg, NAD+.# This type of reaction, which enables one substrate to be oxidized at the expense of another, is particularly useful in enabling oxidative processes to occur in the absence of oxygen, such as during the anaerobic phase of glycolysis.# NADH dehydrogenase acts as a carrier of electrons between NADH and the components of higher redox potential. Other dehydrogenases such as succinate dehydrogenase, acyl-CoA dehydrogenase, and mitochondrial glyceroI-3- phosphate dehydrogenase transfer reducing equivalents directly from the substrate to the respiratory chain.# Both NADH and NADPH donate reducing equivalents for the reduction of these cytochromes.# Most of the energy liberated during the oxidation of carbohydrate, fatty acids, and amino acids is made available within mitochondria as reducing equivalents (?H or electrons).# The reduced NADH of the respiratory chain is in turn oxidized by a metalloflavoprotein enzyme--NADH dehydrogenase. This enzyme contains FeS and FMN, is tightly bound to the respiratory chain, and passes reducing equivalents on to Q.# The pentose phosphate pathway, an alternative to part of the pathway of glycolysis, is a source of reducing equivalents (NADPH) for biosynthesis and the source of ribose for nucleotide and nucleic acid synthesis.# The reducing equivalents from the NADH + H+ formed in glycolysis are taken up into mitochondria for oxidation via one of the two shuttles.# NADPH is involved as donor of reducing equivalents in both the reduction of the 3-ketoacyl and of the 2,3-unsaturated acyl derivatives.Also remember:MAJOR OXIDATIVE PATHWAYS WHICH GENERATE ATP AND NADH ARE:# Glycolysis# Fatty acid oxidation# Citric acid cycle and# Electron transport coupled to oxidative phosphorylation (respiratory or electron transport chain)
NADH + H+
NADPH + H+
FADH2
QH2
Lipids