ATP Yield Per Mole by Functional Group
Direct Answer
Hydrogen atoms yield the most ATP per mole among the functional groups listed, as energy is fundamentally derived from hydrogen through metabolic processes that require oxygen to generate ATP. 1
Biochemical Basis of ATP Production
Hydrogen as the Primary Energy Source
Energy is derived from hydrogen by metabolic processes that require oxygen, with protons shuttling due to a gradient serving as the motor for ATP generation from substrates 1
The transmembrane movement of protons back into mitochondria through ATP-synthase drives the production of ATP from ADP through three fundamental steps: (1) release of hydrogen from water and nutrients, (2) production of a proton gradient during cellular respiration, and (3) production of ATP by consumption of this proton gradient 1
In practical terms, what is measured during energy metabolism is the amount of oxygen consumed for energy production, which directly relates to hydrogen oxidation 1
Comparative ATP Efficiency by Substrate Type
Glucose is the most efficient substrate in terms of ATP production via oxygenation, yielding 120 kcal per liter of oxygen, compared with 100 kcal from fat 1
The difference in efficiency relates to the metabolic pathways utilized: glucose metabolism relies heavily on nicotinamide adenine dinucleotide (NAD), while metabolism of fat uses relatively more flavin adenine dinucleotide (FAD) 1
Fat yields more calories per gram utilized overall, resulting in a lower respiratory quotient (RQ), but this does not translate to superior ATP production per oxygen consumed 1
Functional Group Analysis
Why Other Groups Are Less Efficient
Carboxyl groups (-COOH): These are typically found in metabolic intermediates and represent partially oxidized carbon states, not the primary energy source 1
Carbonyl groups (C=O): Present in many metabolic intermediates but represent intermediate oxidation states rather than primary hydrogen donors 1
Amino groups (-NH2): While amino acids can be catabolized for energy, they are less efficient ATP sources and require deamination before entering energy-producing pathways 1
Oxygen atoms: These serve as the terminal electron acceptor in aerobic respiration but do not themselves yield ATP; they facilitate hydrogen oxidation 1
Double bonds: These represent structural features that may affect the energy content of molecules but are not themselves the primary determinant of ATP yield 1
Clinical Relevance
Thiamine's Role in Hydrogen Metabolism
Thiamine diphosphate (ThDP) is key to ATP production as a coenzyme for enzymes that catalyze hydrogen transfer and is essential for pyruvate dehydrogenase activity 1
Thiamine is essential for carbohydrate metabolism and energy metabolism, serving as an indispensable cofactor for four enzymes involved in ATP production 1
Magnesium must be corrected concomitantly when treating thiamine deficiency, as it is necessary for adequate function of thiamine-dependent enzymes 2
Practical Implications
The theoretical ATP yield from complete glucose oxidation varies among organisms between 26 and 38 ATP molecules per glucose molecule, though older textbook values of 36-38 ATP/hexose overestimate actual yields 3, 4
Plant respiratory ATP yield is approximately 27.5 ATP/hexose from sucrose (0.5 ATP/hexose more from starch), which is smaller than often assumed 4
Actual ATP yield is often smaller than potential yield due to bypasses of energy-conserving reactions in the respiratory chain, even in unstressed conditions 4
Important Caveats
The cellular concentration hierarchy follows [ATP] > [ADP] > [AMP] > [adenosine], and high yields of low-energy metabolites during extraction may indicate artifactual production from more abundant higher-energy species rather than true biological concentrations 1
Incomplete quenching during metabolite measurement can lead to transformation of ATP into ADP, confounding accurate assessment of energy status 1
The ATP:ADP and ATP:AMP ratios are more biologically informative measures of energy status than ATP concentration alone 1