DESCRIBE THE HUMAN CELLS AND HOW THEY HARVEST ENERGY (HOW WE DEAL WITH CARBS, LIPIDS AND PROTEINS.)
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Human cells obtain energy through a complex process called cellular respiration, which involves the breakdown of carbohydrates, lipids, and proteins. Let's take a closer look at how each of these molecules is processed to extract energy:
1. Carbohydrates: The primary source of energy for cells is glucose, a simple sugar derived from carbohydrates. When you consume carbohydrates, they are broken down into glucose molecules through the process of digestion. Glucose is then transported from the bloodstream into cells with the help of insulin. Once inside the cell, glucose undergoes a series of reactions in a process called glycolysis, which occurs in the cytoplasm. Glycolysis converts glucose into two pyruvate molecules, along with a small amount of energy in the form of ATP. The pyruvate produced can either enter the mitochondria to continue the breakdown process or be converted into other compounds.
2. Lipids: The cells can also utilize lipids (fats) as an energy source. Lipids are broken down into fatty acids and glycerol through the process of lipolysis, which occurs primarily in the adipose tissue. Fatty acids are transported into the mitochondria, where a series of reactions called beta-oxidation occurs. This process involves sequentially breaking down the fatty acids into acetyl-CoA molecules and generating ATP in the process. Acetyl-CoA then enters the citric acid cycle (also known as the Krebs cycle or TCA cycle), which occurs in the mitochondria, generating more ATP and reducing molecules such as NADH and FADH2.
3. Proteins: Proteins can also serve as a backup energy source when carbohydrates and lipids are insufficient. Protein breakdown, known as proteolysis, occurs in the digestive system and results in the production of amino acids. Before amino acids can be used for energy, the amino group (NH2) is removed in a process called deamination. The remaining carbon skeleton can then be converted into intermediates of the citric acid cycle to generate ATP.
In summary, human cells harvest energy from carbohydrates, lipids, and proteins by breaking them down into smaller molecules, which then enter various metabolic pathways to generate ATP. The specific process is regulated and coordinated by specific enzymes and occurs within the cytoplasm and mitochondria of the cell.