Metabolic pathways for sugars, fats, and proteins are key for making energy and keeping our bodies balanced.
1. Sugars (Carbohydrates)
- Where We Get Them: Fruits, vegetables, grains, and dairy products.
- How We Break Them Down: It starts in the mouth with saliva, and then continues in the small intestine.
- How Our Bodies Use Them: Simple sugars like glucose and fructose move into our blood.
- Energy Production:
- Glycolysis changes glucose into pyruvate, creating 2 ATP (energy) for each glucose.
- Pyruvate then goes into the citric acid cycle, making NADH and FADH2. These help produce up to 34 ATP through a process called oxidative phosphorylation.
2. Fats (Lipids)
- Where We Get Them: Oils, butter, nuts, and fatty fish.
- How We Break Them Down: Bile salts help break down fats, which are then split apart by enzymes called lipases.
- How Our Bodies Use Them: Fatty acids and monoglycerides are absorbed through the intestines.
- Energy Production:
- Fats go through beta-oxidation, which turns fatty acids into acetyl-CoA that enters the citric acid cycle.
- This generates a lot of energy, about 108 ATP from a single 16-carbon fatty acid.
3. Proteins
- Where We Get Them: Meat, dairy, beans, and nuts.
- How We Break Them Down: It starts in the stomach with the help of an enzyme called pepsin and is finished in the small intestine.
- How Our Bodies Use Them: Amino acids move through the intestinal wall into the blood.
- Energy Production:
- Our bodies can change amino acids into different forms that can be used for energy.
- Gluconeogenesis can make glucose from some amino acids.
This process of breaking down and using sugars, fats, and proteins gives our bodies the energy they need to function every day.