In preparing pyruvate to enter the citric acid cycle, which of the following steps occurs Quizlet

the oxygen atom is very electronegative

The high electronegativity of the oxygen atom is the reason that oxygen gas (O2) is such a good oxidizing agent (why it can oxidize so many compounds). The two atoms of the oxygen molecule (O2) share their electrons equally but, for example, when oxygen reacts with the hydrogen from methane, forming water, the electrons of the covalent bonds spend more time near the oxygen than the hydrogen. In effect, each oxygen atom has partially "gained" electrons, so the oxygen molecule has been reduced. Because oxygen is so electronegative, it is one of the most potent of all oxidizing agents. Energy must be added to pull an electron away from an atom, just as energy is required to push a ball uphill. The more electronegative the atom (the stronger its pull on electrons), the more energy is required to take an electron away from it. An electron loses potential energy when it shifts from a less electronegative atom toward a more electronegative one, just as a ball loses potential energy when it rolls downhill. A redox reaction that moves electrons closer to oxygen, such as the burning (oxidation) of methane, therefore releases chemical energy that can be put to work.

Fats are better electron donors to oxygen than are sugars.

Fats contain more hydrogen and less oxygen than sugars and it is the transfer of electrons from good donors, such as hydrogen atoms, to good acceptors, such as oxygen, that provides the energy in respiration.
Catabolism can also harvest energy stored in fats obtained either from food or from storage cells in the body. After fats are digested to glycerol and fatty acids, the glycerol is converted to glyceraldehyde 3-phosphate, an intermediate of glycolysis. Most of the energy of a fat is stored in the fatty acids. A metabolic sequence called beta oxidation breaks the fatty acids down to two-carbon fragments, which enter the citric acid cycle as acetyl CoA. NADH and FADH2 are also generated during beta oxidation; they can enter the electron transport chain, leading to further ATP production.
Fats make excellent fuel, in large part due to their chemical structure and the high energy level of their electrons (equally shared between carbon and hydrogen) compared to those of carbohydrates. Unfortunately, the high energy yield of fats also means that a person trying to lose weight must work hard to use up fat stored in the body because so many calories are stockpiled in each gram of fat.