![]() ![]() In the pancreas, vesicles store trypsin and chymotrypsin as trypsinogen and chymotrypsinogen. In order to avoid breaking down the proteins that make up the pancreas and small intestine, pancreatic enzymes are released as inactive proenzymes that are only activated in the small intestine. HCl in the stomach aids in proteolysis, and hormones secreted by intestinal cells direct the digestive processes. Enzymes in the stomach and small intestine break down proteins into amino acids. Together, all of these enzymes break complex proteins into smaller individual amino acids, which are then transported across the intestinal mucosa to be used to create new proteins, or to be converted into fats or acetyl CoA and used in the Krebs cycle.įigure 1. ![]() The pancreas releases most of the digestive enzymes, including the proteases trypsin, chymotrypsin, and elastase, which aid protein digestion. Secretin also stimulates the pancreas to release sodium bicarbonate. The small intestine also releases digestive hormones, including secretin and CCK, which stimulate digestive processes to break down the proteins further. This helps to protect the lining of the intestine. When the food-gastric juice mixture (chyme) enters the small intestine, the pancreas releases sodium bicarbonate to neutralize the HCl. Pepsin cuts proteins into smaller polypeptides and their constituent amino acids. The latter produces an environmental pH of 1.5–3.5 that denatures proteins within food. When protein-rich foods enter the stomach, they are greeted by a mixture of the enzyme pepsin and hydrochloric acid (HCl 0.5 percent). The digestion of proteins begins in the stomach. Although the body can synthesize proteins from amino acids, food is an important source of those amino acids, especially because humans cannot synthesize all of the 20 amino acids used to build proteins. Proteins are not stored for later use, so excess proteins must be converted into glucose or triglycerides, and used to supply energy or build energy reserves. ![]() Amid all these necessary functions, proteins also hold the potential to serve as a metabolic fuel source. Protein is also used for growth and repair. That is not even the complete list! There is protein in bones (collagen), muscles, and tendons the hemoglobin that transports oxygen and enzymes that catalyze all biochemical reactions. They represent cell signaling receptors, signaling molecules, structural members, enzymes, intracellular trafficking components, extracellular matrix scaffolds, ion pumps, ion channels, oxygen and CO 2 transporters (hemoglobin). Much of the body is made of protein, and these proteins take on a myriad of forms. Explain how protein can be used for energy.Differentiate between glucogenic and ketogenic amino acids.Explain how the urea cycle prevents toxic concentrations of nitrogen.By the end of this section, you will be able to: ![]()
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