9.3 Digestive Enzymes Flashcards
What are digestive enzymes?
proteins that speed up specific chemical reactions
What is starch?
a carbohydrate that’s digestion begins in the mouth
What is salivary amylase?
an enzyme in saliva that digests starch to maltose
What is maltose?
disaccharide molecule that cannot be absorbed by the intestine
What is glucose?
a monosaccharide that can be absorbed, digestive action in the small intestine converts maltose to glucose
Where does protein digestion begin?
in the stomach
Why are gastric juices secreted by gastric glands very acidic?
(pH 2) because it contains hydrochloric acid
What is pepsinogen?
a precursor that is converted to the enzyme pepsin when exposed to HCl that is present in gastric juice
What is pepsin?
an enzyme that acts on proteins (polymers of amino acids) to produce peptides
Describe peptides from the stomach.
usually too large to be absorbed by the intestinal lining, but later in the small intestine they are broken down to amino acids
What is pancreatic juice?
enters the duodenum and has a basic pH because it contains NaHCO3 (sodium bicarbonate)
What does NaHCO3 do?
neutralizes the acid in chyme, producing the slightly basic pH that is optimum for pancreatic enzymes including pancreatic amylase and trypsin
What is pancreatic amylase?
a pancreatic enzyme that digests starch
What is trypsin?
a pancreatic enzyme that digests protein
What is trypsin secreted as?
trypsinogen, which is converted to trypsin in the duodenum
What is lipase?
a pancreatic enzyme that digests fat molecules in the fat droplets after they have been emulsified by bile salts
What are fats?
triglycerides, composed of glycerol and three fatty acids
What are the end products of lipase digestion?
glycerol and fatty acid molecules that are small enough to cross the cells of the intestinal villi where absoprtion takes place
glycerol and fatty acids enter the cells of the villi, and within these cells, they are rejoined and packaged as lipoprotein droplets before entering the lacteals
What is peptidases?
enzyme secreted by the surface cells of the small intestine villi and completes the digestion of proteins to amino acids
What is maltase?
enzyme secreted by the surface cells of the small intestine villi and completes the digestion of starch to glucose
What is lactose intolerance caused by?
fermentation of of non-digested lactose by intestinal bacteria
When do enzymes function best?
at an optimum temperature and pH, which helps maintain the proper shape to fit their substrate
What does the compartmentalization of the digestive system do?
assists in the regulation of enzymatic activity
Why is enzymatic activity largely controlled by pH?
because the entire digestive system of humans is maintained at a constant temperature of 37 C
What is the pH of the stomach?
between 1 and 2, allowing the activation of pepsinogen enzyme
When does the pH of the stomach change?
shortly after chyme proceeds into the duodenum, the sodium bicarbonate released from the pancreas returns the pH to around 7.4-7.8
What does the change in pH of the stomach do?
serves the activate digestive enzymes released by the pancreas, thus allowing the digestion of carbohydrates, fats, and proteins
