Individuals on low-fat, low protein diets obtain the bulk of their energy needs from carbohydrates.?

Question

Complex carbohydrates such as starch and disaccharides such as sucrose (table sugar) are first broken down into glucose. Through a series of metabolic reactions and pathways, the glucose is completely converted to CO2, and the energy it contains is used to produce glucose. Can anyone describe this process in detail?

Answer 1

Science teacher is right that there seems to be a problem with the last part of the last sentence. There is, however, one process that humans use to 'produce' glucose, but they can't do it using CO2. This process is called 'gluconeogenesis', where gluco=glucose, neo=new, genesis=creation.

The complex carbs and disaccharides such as sucrose are broken down into glucose. The series of metabolic reactions are numerous and complex (need good chemistry knowledge for good understanding), but the pathways themselves are easier to summarize:

Glycolysis (breaking or cutting of glucose) essentially 'breaks' the 6-Carbon glucose molecule into two 3-carbon molecules of pyruvate (in some books, referred to as pyruvic acid).

Pyruvate is then degraded to CO2 in a pathway known as either tricarboxylic acid cycle (TCA cycle) or Kreb's cycle. The key to the TCA cycle is the removal of electrons and hydrogen ions (H+) from the pyruvate, which are then used in the next pathway.

The final energy-producing pathway is known as the electron transport system, or in some books the chemiosmotic pathway. This is where the electrons and H+s are used to produce the majority of energy (in the form of ATP); this is also where O2 comes in to the story. The electrons and H+s are added to the O2 molecule to form 2 molecules of H2O.

Fabulous, isn't it?

Answer 2

There seemed to be an improper step in your process. Yes glucose is broken down into CO2 and H2O. Then you say the energy it contains is used to produce glucose. Animals do not produce glucose. The energy is obtained as the glucose is broken down. Individua;s on low fat, low protein diets get their energy from complex carbohydrates.