Glycolysis and Cellular Respiration
GlycolysisSometimes, it can be confusing to keep track of what is being oxidized and what is being reduced. Using the trick about the phrase "LEO the lion says GER" helps us remember which is which…but looking at the charge of a molecule can also clue you in about where electrons are going. If a molecule is sporting a + sign (such as NAD+), that is a good sign that it needs an electron. It will likely be reduced, gain an electron, and become neutrally charged, or, not charged at all.
Glycolysis breaks down glucose, so you might think that glucose is the only form of energy acceptable to animals, including humans. On the contrary, glucose is rare in our diets. We eat lots of other sugars (despite the dentist's advice), including sucrose, fructose, and lactose, but not a lot of plain old glucose. The good news is that our bodies can convert other compounds into glucose, including proteins and fats.
Glycolysis is presented here as the first step in cellular respiration, which it is. However, it can also exist without the rest of cellular respiration—organisms that undergo fermentation in anaerobic environments undergo glycolysis, too.
Citric Acid CycleBecause the citric acid cycle makes many different compounds, it is easy to lose track of the main product of the citric acid cycle: energy. The main point of the citric acid cycle is to change pyruvate into ATP, NADH, and FADH2. Pyruvate that originally came from glucose is oxidized in a series of steps that result in ATP, NADH, and FADH2. ATP is energy, and NADH and FADH2 equal energy, too, after they go through the electron transport chain.
FermentationAnaerobic sounds a little bit too much like aerobic for some people's liking. The "aerobic" part means oxygen, and "an" means "no," so anaerobic means "no oxygen." Just remember: you don't have the guts to do anaerobic respiration, but cow guts do.
Carbon dioxide is only produced in alcohol fermentation and not lactic acid fermentation.