Energy yield

How many net ATP molecules are obtained in glycolysis per glucose molecule, and how many in total (classic theoretical figure) when completely respired aerobically?

State how many ATP molecules are obtained, according to currently accepted values, for each NADH and for each $\text{FADH}_2$ that deliver their electrons to the respiratory chain.

In aerobic respiration, about $36$-$38\ \text{ATP}$ are obtained per glucose, of which only $2$ come from glycolysis. Calculate what percentage of the total yield is contributed by the mitochondrial stages (taking $36\ \text{ATP}$ as the total) and comment on the result.

Why is fermentation much less energy-efficient than aerobic respiration, even though both begin with glycolysis? Explain what happens to pyruvate in each case.

Rank from highest to lowest energy yield per glucose molecule: aerobic respiration, lactic acid fermentation, and alcoholic fermentation. Justify the ranking.

Calculate how many glucose molecules a cell needs to break down to obtain $180\ \text{ATP}$ aerobically ($36\ \text{ATP/glucosa}$) and how many by fermentation ($2\ \text{ATP/glucosa}$). Comment on the implication of this difference for anaerobic organisms.

What does it mean that a metabolic pathway has an energy yield of $40\ \%$? Explain what happens to the rest of the energy contained in the food.

The combustion of $1\ \text{g}$ of glucose releases about $4\ \text{kcal}$ and that of $1\ \text{g}$ of fat about $9\ \text{kcal}$. Explain what that difference is due to and calculate how many grams of fat provide the same energy as $90\ \text{g}$ of glucose.

Under standard biochemical conditions ($\text{pH} = 7{,}0$, $25\ ^\circ\text{C}$), the complete combustion of $1\ \text{mol}$ of glucose yields $\Delta G^{\circ\prime} = -2870\ \text{kJ/mol}$ and the hydrolysis of $1\ \text{mol}$ of ATP yields $\Delta G^{\circ\prime} = -30{,}5\ \text{kJ/mol}$. However, in the cytoplasm of a living hepatocyte, the actual concentrations of ATP, ADP, and $\text{P}_\text{i}$ mean that the phosphorylation of ADP requires around $+50{,}0\ \text{kJ/mol}$, with roughly $30\ \text{mol of ATP}$ net per mole of oxidized glucose obtained experimentally.

1. a) Calculate and compare the theoretical percentage energy efficiency under standard conditions (assuming $36\ \text{ATP/glucose}$) versus the actual intracellular thermodynamic efficiency. Justify the fate of the fraction of free energy that is not stored in the phosphate bonds of ATP and its significance for homeothermic animals.
2. b) 2,4-Dinitrophenol (DNP) is a lipophilic molecule capable of transporting protons across the inner mitochondrial membrane, dissipating the electrochemical gradient. Predict, with reasoning, how treatment with DNP will affect the net yield of ATP per glucose, the rate of $\text{O}_2$ consumption by the cell, and the body temperature of the organism.

During a marathon, a runner performs about $10000\ \text{kJ}$ of useful work. If their organism has an overall yield of $25\ \%$, calculate how much chemical energy from food they have had to mobilise and reason why their body heats up so much during the race.

The adult human brain has a mass of about $1400\ \text{g}$ (around $2\ \%$ of body mass), but at rest it consumes $20\ \%$ of the oxygen and glucose of the entire body, degrading approximately $120\ \text{g}$ of glucose per day (molar mass $= 180\ \text{g/mol}$).

1. a) Justify at a molecular and membrane transport level which continuous physiological processes of neurons explain such a basal expenditure of ATP at rest.
2. b) Calculate the daily moles of ATP produced by the brain assuming a net yield of $30\ \text{mol of ATP}$ per mole of oxidized glucose. If the total intracellular reserve of ATP in brain tissue is $2{,}5\ \mu\text{mol/g}$, calculate how many seconds of activity this reserve would last if oxidative phosphorylation were stopped instantaneously.
3. c) Based on the results of b), justify why cerebral ischemia causes loss of consciousness in less than $10\ \text{seconds}$, and explain why the brain cannot sustain its energy viability through fermentation from endogenous glycogen, unlike skeletal muscle fibers.

A migratory bird weighing $30\ \text{g}$ must face an uninterrupted journey requiring a metabolic energy expenditure equivalent to $2\ \text{mol}$ of ATP.

Data:

• Glucose: $180\ \text{g/mol}$; yield = $36\ \text{mol}$ of ATP per mole of glucose. Glycogen is stored hydrated with $2\ \text{g}$ of water per gram of dry polysaccharide.

• Palmitic acid: $256\ \text{g/mol}$; yield = $106\ \text{mol}$ of ATP per mole of fatty acid. Triacylglycerols are stored in anhydrous form.

1. a) Calculate the total reserve mass (in grams) that the bird should incorporate into its body before the journey if it stored that energy exclusively as fat versus if it did so exclusively as hydrated glycogen.
2. b) Based on the results obtained, interpret the biomechanical impact on flight and predict what would happen to the viability of migration if glycogen were used.
3. c) Justify biochemically why one dry gram of palmitic acid yields more than double the ATP of one gram of glucose, considering the oxidation state of their carbon atoms.