Biology Forum Cell Biology Food to ATP energy?

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    • #17836

      Hi everyone,

      I have read the Forum Rules, however I am new to this forum and I apologize in advance if somehow this question is not acceptable.
      I also am not sure if this is the right category, as the questions seem to pertain to many concepts.

      I am not a biologist but the following is my understanding:
      I suppose humans have an average daily intake of 2,000 calories in the form of food, using an average of 90 calories per hour while idle and awake.
      I suppose this food is digested and separated into nutrients such as carbohydrates, proteins and fats. I guess this is a process during which the food looses some of the energy as our digestive system does not operate under 100% efficiency.
      I also suppose some of the energy is lost during the oxidation of those nutritients as well. The rest of the energy is used to convert ATD to ATP.
      Now, in one of my mothers older medical books, and many links on the internet afterwards (such as this one, I have found it says that just one mole of ATP can generate 8000 calories!

      My question is how the human body can need and spend so little calories, but create so much energy in the form of ATP (1 billion of calories worth per day if you are to believe the link)?
      And how is all this energy surplus used? There is no way so much of it is lost to heat as I also read that the energy efficiency of the human body is around 25%. Can it be used at all or is it lost in some other way?


    • #115296

      The recommended daily intake is more than 2000 kilocalories! … ily_intake
      The daily turnover of ATP is equivalent of about 1000 kcal.

    • #115366

      It seems that you may have a misunderstanding between the meaning of calorie and Calorie (with a capital "C"). a lowercase "C" indicates a true calorie, and an upper case "C" represents a kilocalorie. We use the upper case "C" when talking about foods and the lower case "c" when talking about metabolism. Your 8000 calories is really only 8 Calories.

      The rest of this reply is going to be a little bit Math-intense, but I’ll try to summarize at the end (I think I answered the bulk of your issue above):

      The molecular weight of glucose is ~180 grams/mol. That means one mole of glucose weighs 180 grams. One mole of glucose could, at 100% efficiency (theoretical yield) be converted into about 30 moles of ATP.
      Many biology textbooks will state 38, but they do not account for the cost of transporting pyruvate and ADP into the mitochondria, and other costs to move molecules for the entire process.

      There are ~4 kilocalories, our ~4 Calories (with a capitol "C") in each gram of glucose (it’s really closer to 3.75). Therefore 180 grams of glucose would contain about 675-720 kilocalories (Depending on how you calibrate the calorimeter). and would produce 30 mole of ATP from ADP (if the glucose is used entirely for ATP production).
      – It should be noted that not all molecules of glucose are used in ATP production. Some are used to produce lactic acid, glycogen, glycerol, fat, and I’m sure there are other metabolites that I’m not thinking of.

      When glucose is consumed in excess (eating more calories than you burn), you will store glucose as fat. This is done in a multi-step process called a biochemical pathway.

      One mole of ATP can be oxidized to ADP and releases about 7.3 kilocalories in that process. So, the 30 moles of ATP produced can only be converted into 219 kilocalories. That means glucose oxidation releases most of its heat during the process of making ATP (Lucky you!) .
      Now, 7.3kilocalories is the same as 7,300 calories (or 7.3 Calories with a capital "C").

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