Experiment 9 Chemical Digestion of Foods

(digestive system) (carbohydrates, proteins, lipids) (intestines) (transported) (vasculature) (tissues and cells) (mastication and chemical digestion).

The function of the (_____________) is to break down large food molecules (_______, ______, ______) into the smaller subunits that make them up. This process ensures molecules following digestion are small enough to be absorbed within the (___________) and then (___________) through the (___________) of the body to the (____________) where those molecules can then be used. The means by which food is broken down following (_____and______).

(proteins) (37oC) (above or below) (60oC) (denatured) (decrease) (0oC) (pH sensitivity) (acidic pH (2.0)

One must remember that enzymes are (________) and since enzymes are (1) (_______), the environment that they are found will affect their effectiveness. For humans, digestive enzymes function the best at temperatures of (______) and will be drastically impacted by temperatures (______or______) this temperature. Being heated above (_______) will lead to the protein being (_________) and thus will no longer function properly. Conversely being cooled will progressively (________) activity for some enzymes to the point of no activity once a temperature of (_____) is reached. Additionally, enzymes will function within an optimal range based on (__________) of the molecule. This (9) (____________) is an indication as to where within the pathway of digestion the enzyme will principally function. An example of this would-be pepsinogen that must be exposed to the (___________) within the gastric secretions to become active and digest proteins into short-polypeptide chains.

(polar environment) (alimentary canal) (emulsification) (bile salts)

Lastly, the ability for the enzymes within the (_____________) of the (____________) to interact with non-polar substances will be dependent upon the (____________) that comes about through the exposure and interaction with (__________).

(mucus, bile salts, bilirubin, hydrochloric acid (HCl), and sodium bicarbonate (NaHCO3) (digestive enzymes) (not occur) (HCl and NaHCO3)

The Importance of Enzymes in Chemical Digestion

There are many different substances that are secreted into the different segments of the alimentary canal. Many of these substances facilitate the breakdown of food (i.e. _______, _____, ___, _________, ______). However, the most important substances secreted for the purpose of digestion are the (_____________). (2) (______________) greatly enhance the rate at which the covalent bonds that link subunits together to form polymeric biomolecules are broken. Indeed, without the presence of these enzymes, chemical digestion would essentially (________). Although substances such as (_____&____) can alter non-covalent bonding patterns within and among biomolecules, they typically cannot break down covalent bonds.

(alimentary canal) (accessory organs) (substrate) (carbohydrates) (simpler carbohydrates) (lipids) (glycerol and free-fatty acids) (amino acid units) (not digest)

These enzymes within the (______________) (stomach and intestines) and secreted by the (____________) (liver, pancreas, salivary glands, gall bladder) will perform the action of digestion based on specificity to a (________). Where some enzymes will digest complex (___________) (polysaccharides) into (____________) (disaccharides and monosaccharides), while others will only digest (_____) (large fatty acids and triglycerides) into (_______________________), and others will digest proteins into their (______________). In which an enzyme that digest the carbohydrate will (______) the lipid or the protein, and the enzyme for the lipid will not digest the carbohydrate or protein, nor will the enzyme for protein digestion digest the carbohydrate or lipid.

(Carbohydrates) (oral cavity) (salivary amylase) (ptyalin) (polysaccharide amylose) (disaccharide maltose) (stops)

(_____________) are the first type of biomolecule to be chemically digested in the alimentary canal, as chemical digestion begins in the (_________) through a salivary enzyme called (______________) (or (_____). (3) (____________) begins the breakdown of the (____________) (starch, the principal storage carbohydrate in plants) into the (_______________). However, when food is swallowed and transferred to the small intestine, chemical digestion of carbohydrates effectively (______).

(chyme) (pancreatic amylase) (starch and glycogen) (disaccharides and oligosaccharides) (brush-border enzymes) (intestinal epithelium)

Only when the (________) passes into the small intestine will carbohydrate digestion resume. In the small intestine the (1) (_______) is exposed to (______________) (which continues the process of breaking down (______&______) into (__________&____________) and certain (_____________) (e.g., lactase, sucrase, and maltase) that break down specific oligosaccharides into the monosaccharides that are absorbed by the (_____________).

(stomach) (gastric juice) (neural stimulation) (changes) (hydrochloric acid (HCl) and the protease pepsin)

Chemical digestion of protein begins in the (_________). The (1) (__________) produces a mixture of fluids called (_________) in response to (___________) (induced by smell, site, and taste of food), by distension of the stomach as food enters, and by pH (_______) induced as the more neutral pH food enters the acidic stomach. Gastric juice contains several substances, but the two most important for initiating protein digestion are (_______&________).

(HCl) (parietal cells) (gastric mucosa) (denatures the tertiary structures) (pepsin)

(____) is secreted by (________) in the (_________). The low pH (~2) of the gastric juice aids protein digestion in a couple of ways. First, the low pH (________________) of ingested protein, making them easier to digest enzymatically. Secondly, the low pH is required for the activation of (________).

(chief cells) (pepsinogen) (weak proteolytic) (peptide bonds) (amino acids) (hydrophobic side chains)

Pepsin is produced by (_______) of the gastric pit in the molecule’s inactive form called (________), but once it diffuses into the lumen of the stomach the acidic conditions enable it to have a (__________) activity). (3) (__________) can digest some ingested protein, but more importantly (3) (___________) molecules will partially digest one another, removing inhibitory segments of the polypeptide chain and thus converting each other into the fully active enzyme pepsin. Pepsin breaks (_________) between (_______) with (_______________) in the middle of polypeptides, thus it cleaves long polypeptides into shorter polypeptides.

(small intestine) (gastrostomies) (homogenization) (chemical and physical)

Although the chemical digestion of protein begins in the stomach through the actions of pepsin, most of the digestion of protein takes place in the (_______). Indeed, individuals with complete (________) can still completely digest protein, although the (____________) of chyme through (______&_______) digestion in the stomach aids this process.

proteases) (membrane bound) (brush-border) (pancreas) (pyloric sphincter)

The (________) that function in the small intestine comes from two major sources: (___________) enzymes on the (_________) of the intestinal mucosa, and enzymes secreted into the small intestine from the (________). The pancreatic enzymes, along with bicarbonate salts, are components of pancreatic juice that is secreted primarily when food enters the small intestine through the (__________).

(hormones secretin) (water and bicarbonate) (cholecystokinin (CCK) (duodenal papilla)

Chemicals in the chyme induce cells in the small intestine to secrete the (_____________), which stimulates (_______&_______) secretion in the pancreas, and (____________), which stimulates enzyme secretion in the pancreas. These hormones, in turn, cause the pancreas to release pancreatic juice through the (___________).

(pancreatic juice) (zymogens) (free amino acids, dipeptides, and oligopeptide) (intestinal epithelium)

A few different proteases are found within (___________), but most are released as (_________) (inactive enzymes). Enzymes in the brush-border activate these (2) (___________), which ultimately digest the polypeptides into a combination of (____, _______, and _____) that are absorbed by (___________).

(Lipids) (hydrophobic) (large droplets) (water soluble) (triglyceride)

(_____) are a particularly challenging group of molecules to chemically digest, as fats being (_________) tend to aggregate into (_________) within the water environment of the alimentary canal. The result of the aggregation minimizes the surface area of contact between the fat and the surrounding water. Since the digestive enzymes are (__________), they can only come into contact with and digest those (___________) molecules at the surface of the droplets.

(surface area) (enzymes) (substrate)

Thus, for fat digestion to be efficient, the large droplets must be broken into much smaller droplets and held in these smaller droplets to increase (_________) and enable (________) (lipases) adequate contact with their (_________).

(gastric lipase) (stomach) (fat digestion) (salivary lipase) (pancreatic and intestinal brush) (liver and gall bladder)

Although there is a (_________) secreted in the (________) that causes a small amount of (__________), and infants produce a (__________), almost all the digestion of fat takes place in the small intestine. Like protein digestion, fat digestion is achieved through the activity of both (______&_____________) border lipases. However, efficient fat digestion also involves the secretion of bile from the (_____&________).

(Bile) (bile salts) (emulsify) (large fat droplets)

(___) contains a mixture of bilirubin, cholesterol, phospholipids, inorganic ions, phospholipids, and negatively charged cholesterol derivatives called (______) that functions to (_______) the lipids in the water of the alimentary canal assisting the digestion of the (___________).

(triglycerides) (hydrolyze) (amphipathic free fatty acids) (monoglyceride) (intestinal epithelium)

The interaction with bile in the small intestine greatly increases the surface area over which lipases can come into contact with the (_________) and (_________) them into (_________________) and (______________), both of which can be absorbed by the (____________).

(pH) (bicarbonate) (pancreatic juice’s)

The liberation of free fatty acids, which are acids, would lead to a decrease in the (___) of the fluid passing through the intestine, although normally the presence of (___________) in the (____________) buffers against a decrease in (1) (___).