PROTEIN SECTION LECTURE #3 Flashcards
Where does protein digestion start in the human body?
Protein digestion starts in the stomach.
What role does the hormone gastrin play in protein digestion?
Gastrin triggers stomach churning and the release of gastric juice, which is essential for the digestion of proteins.
How does hydrochloric acid (HCl) facilitate protein digestion?
HCl denatures and unravels proteins and converts pepsinogen to pepsin, which then begins to digest proteins by hydrolyzing peptide bonds.
Why is mucus important in the stomach during protein digestion?
Mucus is important because it protects the stomach lining from the acidic environment and the enzymatic activity of pepsin and HCl.
Why do chief cells of the stomach secrete pepsinogen rather than active pepsin?
Chief cells secrete pepsinogen, which is an inactive form of pepsin, to prevent the enzyme from digesting the stomach cells themselves. Pepsinogen is converted to active pepsin by HCl in the stomach only when it is needed for digestion.
In what type of environment does pepsin operate, and why is this important?
Pepsin operates in an acidic environment, which is important because it ensures that the enzyme is active only in the stomach where it is needed, preventing it from damaging other tissues.
What is chyme, and where does it go after leaving the stomach?
Chyme is the mixture of partially digested proteins and other foodstuff. It enters the small intestine through the pyloric sphincter after leaving the stomach.
How is the acidity of chyme neutralized in the small intestine?
Secretin stimulates the pancreas to release bicarbonate into the small intestine, which neutralizes the acidity of the chyme.
What happens to proteins after they have been partially digested by pepsin?
After partial digestion by pepsin, proteins are further broken down by enzymes released from the pancreas, such as trypsin and chymotrypsin, into smaller peptide chains and eventually into individual amino acids in the small intestine.
Where are most amino acids absorbed in the small intestine?
Most amino acids are absorbed at the brush border in the proximal third of the small intestine, which includes the duodenum and the upper portion of the jejunum.
What type of cells in the small intestine have amino acid transporters?
Enterocytes, the cells lining the small intestine, have amino acid transporters.
How are amino acids transported across the brush border membrane?
Amino acids are carried from the lumen across the brush border membrane to the enterocyte via sodium-dependent transporters, which is a type of active transport.
Can the absorption rate of amino acids be affected by diet?
Yes, since several amino acids compete for the same transporter, the ingestion of large amounts of one amino acid or groups of amino acids may affect the rate of absorption of other amino acids.
Are only free amino acids absorbed into the villi of the enterocyte?
No, sometimes intact small peptides also get absorbed into the villi of the enterocyte, not just free amino acids.
What happens to amino acids once they are inside the enterocyte?
Inside the enterocyte, amino acids are sometimes broken down into free amino acids by brush border enzymes. If not needed, they can be secreted into the bloodstream (circulation).
