Week 15: Digestion Lab

The optimal pH for pepsin activity is _______.

2

Controls provide a standard of comparison for test results. Each assay contains one or more controls. Positive controls contain all the required substances and a positive result is expected. Negative controls do not contain all the required substances and a negative result is expected. Which of following is a positive control for an IKI (Lugol's) test?

Starch + water

What does a strong IKI result indicate?

Substrate is present.

IKI is used to test for the presence of _______.

starch

Which of the following enzyme/substrate combinations is matched INCORRECTLY? • cellulose - cellulase • peptides - peptidase • starch - amylase • All are matched correctly.

All are matched correctly.

What occurred when pepsin was boiled?

It was inactivated.

Why is gastric lipase NOT as active as pancreatic lipase?

The pH of the stomach is too low and no bile is present in the stomach.

Match these prefixes, suffixes and roots to their meanings.

The root word -stalsis means "constriction." The root word chol- means "bile." The root word glyco- means "sugar." The root word mastico- means "chew."

The building blocks for peptides are _______.

amino acids

Pepsin is classified as _______.

an enzyme and a peptidase

The cellulase in this experiment came from _______.

bacteria

Substrates are held in the active site by _______.

hydrogen and ionic bonds

The presence of reducing sugars _______.

is detected using Benedict's reagent

Enzymes are _______.

made of protein and are catalysts

Prior to lipase digestion of triglycerides, the solution would be _______.

more basic

When using the Benedict's assay, which color would indicate the most reducing sugar present?

reddish brown

The substance that the enzyme acts on is called its _______.

substrate

Which tubes demonstrated amylase activity with a small amount of reducing sugar produced?

tubes 7 and 8

The most unsaturated fats have ...

the most double bonds. Every double bond is a place where hydrogen could be added.

Which of following does NOT secrete a lipase? -the salivary glands -the small intestine -the stomach -the pancreas

the small intestine

The substrate of lipase is _______.

triglyceride

What did the results of tube 3 demonstrate?

Amylase does not digest cellulose.

Amylase is secreted by _______.

both the salivary glands and the pancreas

Which test tube had the highest lipase activity?

tube 1

A food company hydrogenated a barrel of fat. The treatment ...

(a) made the fat less fluid. Hydrogenation removes double bonds, so the tails can straighten. Do you know why that makes the fats less fluid?

What do fats, steroids, and waxes have in common?

(b) Low solubility in water. Low water solubility is the trait that defines lipids.

Enzymes are necessary for digestion of carbohydrates, lipids, and proteins. Which of the following statements are FALSE regarding enzymes? Select all that apply. -Enzymes have specificity. -Enzymes are protein catalysts. -Enzymes are always functional. -Enzymes are altered in reactions. -Enzymes are involved in catabolic and anabolic reactions.

-Enzymes are always functional. -Enzymes are altered in reactions. Enzymes are protein catalysts that lower activation energy so a chemical reaction may proceed. Enzymes are specific, used in both catabolic and anabolic reactions, and remain unaltered during these reactions. However, enzymes can be denatured which renders the enzyme nonfunctional.

Ninhydrin is a chemical that reacts with amino acids in proteins to produce a purple color. The ninhydrin test was performed on three substances: distilled water, apple cider, and egg whites (which contain albumin protein). Match the substances, listed at the left, with the correct descriptions at the right. Match the words in the left column to the appropriate blanks in the sentences on the right. Make certain each sentence is complete before submitting your answer.

1. Positive control: Apple cider 2. Negative control: Egg whites 3. Experimental substance: Distilled water

Match the term at the left with the appropriate description at the right. Match the words in the left column to the appropriate blanks in the sentences on the right. Make certain each sentence is complete before submitting your answer.

1. This solution is used to detect the presence of disaccharides in a solution: Benedict 19s solution 2. In the small intestine, maltose is broken down to this monosaccharide: Glucose 3. This solution is used to detect the presence of starch in a solution: IKI solution 4. This disaccharide is the end product of starch digestion in the oral cavity: Maltose 5. The first step in the digestion of starch in the oral cavity is the formation of these small polysaccharide molecules: Dextrins 6. This carbohydrate-digesting enzyme is produced by salivary glands: Amylase

There are methods of treating and living with celiac disease. Select the treatment method that you think would be most beneficial.

A gluten-free diet Individuals with celiac disease must change their diet and avoid any gluten-containing foods. There are many foods produced as gluten free (GF), which allow individuals with celiac disease a variety of options.

Triglycerides _______. -are digested by lipase -dissolve poorly in water -are lipids -are fats -All of the above are true.

All of the above are true.

There are several different assays to detect the products of digestive enzymes (hydrolases). Since chemical changes cannot be seen with the naked eye, these assays require the use of a color-changing indicator. What chemical indicator, when added to a solution and heated, changes from blue to green to orange in the presence of reducing sugars?

Benedict's solution

Drag and drop the correct statements in the correct sequence of events.

Carbohydrate digestion begins in the mouth through the action of salivary amylase. The digestion continues in the stomach until amylase is inactivated due to the low pH environment of the stomach. The di- and trisaccharides enter the small intestine where additional enzymes continue the breakdown into the resulting monosaccharides. These monosaccharides are absorbed into intestinal cells and diffuse into the intestinal capillaries. The blood in these capillaries eventually flows to the liver via the hepatic portal vein. In the liver, the monosaccharide glucose is stored as glycogen for future use.

Match these vocabulary terms to their meanings.

Constriction that moves food through the alimentary canal is peristalsis. The formation of glycogen from glucose is called glycogenesis. The gallbladder releases bile in response to cholecystokinin. Chewing and grinding food is called mastication.

Celiac disease affects the small intestine. The immune system attacks the gluten protein found in wheat, rye and barely, and also damages the lining of the small intestine. What is the primary function of the small intestine?

It is the primary site of chemical digestion and absorption of nutrients. The small intestine has adaptations such as villi and microvilli to increase surface area so it can absorb nutrients from our food. It also includes the brush border cells, which produces enzymes for chemical digestion to occur. Most absorption of nutrients occurs in the small intestine and when this lining is damaged the ability to process and absorb food is decreased.

How does lactose intolerance affect digestion?

Lactose is not digested. It remains in the intestinal lumen and acts as an osmotic particle. Water is pulled into the intestine, and severe diarrhea results.

Celiac disease can also cause more significant issues in the digestive system. Based on your knowledge of the function of the small intestine, which of the following do you think may occur as a result of the resulting inflammation and damage to the lining of the small intestine?

Loss of the villi surface area and a decrease in absorption of nutrients, causing malabsorption. The immune system attack on the mucosa layer of the small intestine results in a loss of villi. This significantly reduces the surface area available for the absorption of the nutrients. The individual will be malnourished no matter how much he or she eats. This can cause weight loss and decrease growth in children. David has had weight loss, diarrhea, and a decrease in his blood iron levels from the loss of villi.

Drag and drop the terms at the left to match the appropriate descriptions at the right.

Lugols solution: reagent for starch test. Pepsin: enzyme that digests protein. Benedicts reagent: reagent for sugar test. Substrate: molecule that an enzyme reacts with. Lipase: enzyme that digests triglycerides. Amylase: enzyme that digests carbohydrates. Product: substance created in a chemical reaction. Pepsinogen: proenzyme. Biurets reagent: reagent for protein test. Hydrochloric acid: activates stomach enzymes.

Drag and drop the correct statements in the correct sequence of events.

Monoglycerides and triglycerides are common dietary lipids. Triglycerides are broken down into glycerol and fatty acids through the action of enzymes known as lipases. Lingual lipase is released in the mouth and pancreatic lipase is released by the pancreas into the small intestine. The majority of lipid breakdown and absorption occurs in the small intestine. New triglycerides are synthesized within the intestinal cells and packaged into chylomicrons that enter lacteals and circulate within the lymphatic system before entering the circulatory system at the subclavian veins to be transported to the liver, other organs, and cells for use or storage.

In the stomach, parietal cells produce hydrochloric acid, which is needed to convert the proenzyme pepsinogen to the protein-digesting enzyme pepsin. Hydrochloric acid dramatically lowers the pH of the stomach contents to around 2.5. When saliva is swallowed will amylase continue to be functional when it enters the stomach?

No, amylase requires a higher pH. The low pH inactivates the enzyme.

After reviewing the digestive processes for carbohydrates, proteins, and lipids, place the description into the correct bin.

Starch and sugar molecules are classified as carbohydrates. Carbohydrates are the primary energy sources of cellular production of ATP. Monosaccharides are the building blocks of carbohydrates and are used to build larger sugar and starch molecules. Proteins have many important functional and structural roles in the body. Proteins make up the cytoskeleton in cells and function as enzymes. Meats and vegetables are important dietary sources of proteins providing amino acids which are the building blocks of proteins. Although lipids have a bad reputation, they are necessary for the normal functioning of the body. Lipids form cellular membranes and are the basis for certain hormones such as estrogen and testosterone. Most dietary lipids are monoglycerides and triglycerides.

Like blood and other body fluids, saliva can be collected at a crime scene and used for DNA analysis during a forensic investigation. DNA is found in cells, but saliva is an acellular fluid. What do you think is the origin of the DNA found in saliva?

The DNA is found in the epithelial cells that are sloughed off due to friction in the mouth.

Drag and drop the correct terms on the left to complete the sentences. Words may be used once, more than once, or not at all.

The shape of the enzyme provides a pocket called the active site, which allows the substrate to temporarily attach. The substrate is the molecule that is acted on by the enzyme. Enzyme is a protein that speeds up the rate of a chemical reaction without being permanently changed. The product is the result of the enzyme catalysis.

Why was a warm-water bath used to incubate all solutions in all three activities?

The warm-water bath provides the optimal temperature for enzyme activity.

What is the difference between cellulose and starch?

They are linked differently.

What do DNA, proteins, and fats have in common?

They contain carbonyl groups.

Dr. Haxton told one of his students, "To move in the bloodstream, fats need the help of phospholipids." What would a good student say?

Yes. Nonpolar molecules aren't compatible with water. Water rejects nonpolar molecules such as fats, so fats travel inside particles that are coated with polar parts of phospholipids and proteins.

When BAPNA is hydrolyzed, it _______.

changes from colorless to yellow

Pepsin is secreted by _______.

chief cells

The highlighted part of this molecule is derived from ...

glycerol. The other parts of the molecule are derived from fatty acids.

In fat synthesis,________and fatty acids combine to make fats plus________.

glycerol; water Water is a by-product of the reaction that makes ester links between glycerol and fatty acids.

In the reaction that builds a fat,________ groups react with ________ groups.

hydroxyl; carboxyl Fatty acids supply the carboxyl groups; the hydroxyls come from glycerol.

Adding bile to triglycerides _______.

increases the surface area of the triglycerides

Which test tubes were used to determine the optimal pH for lipase activity?

tubes 1, 5, and 6

Which test tubes were used to determine the optimal pH for pepsin activity?

tubes 2, 5, and 6

Maltose is a _______.

disaccharide

The proteins we consume in our diets are broken down to amino acids. Which of the following are events in the process of protein digestion? Select all that apply. -Dipeptidases on the intestinal surface break down short peptides into amino acids -Amino acids transported by intestinal capillaries -Transported as chylomicrons -Bile salts released in the small intestine -Pepsin released in the stomach

-Dipeptidases on the intestinal surface break down short peptides into amino acids -Amino acids transported by intestinal capillaries -Pepsin released in the stomach Proteins are composed of long chains of amino acids that are bonded together by peptide bonds. Pepsin, an enzyme released by cells of the stomach, breaks down peptide bonds resulting in shorter peptide chains. The short chains are further broken down by dipeptidases of the intestinal mucosa, ultimately releasing amino acids. The amino acids move into the intestinal cells and diffuse into the intestinal capillaries. Blood from the intestinal capillaries flows to the liver via the hepatic portal vein.

A blood test that can be used to see if celiac disease is possible is the tissue transglutaminase (tTG)-IgA antibodies (tTG-IgA test). Why do you think this test is a good tool as a screening for possible celiac disease?

Antibodies are produced by B cells of the immune system in response to specific antigens. In celiac disease, the immune system recognizes gluten as an allergen and produces antibodies against it. One mechanism the immune system uses to defend the body is the production of antibodies by B cells. These antibodies are formed in response to a specific antigen. In the case of celiac disease, this antigen is gluten. Since gluten is absorbed in the small intestine, the antibodies also damage the small intestine lining and cause inflammation of the mucosa layer.

Which of the following describes the effect of boiling and freezing?

Boiling denatured the enzyme, but freezing had no effect.

The presence of many C-C and C-H bonds causes fats to be ... (a) rich in energy. (b) insoluble in water. (c) low in energy. Both (a) and (b). Both (b) and (c).

Both (a) and (b). The many C-C and C-H bonds make fats nonpolar and insoluble in water. They can also be oxidized, releasing much energy.

Triglycerides vary with respect to the number of ... (a) hydrocarbon tails. (b) C atoms in the tails. (c) double bonds in the tails. Both (b) and (c). All of the above.

Both (b) and (c). Tail lengths of 16 to 22 are common. There may be from 0 to 6 double bonds.

Clinical Scenario: The Digestive System - Celiac Disease

David is a 12-year-old boy who loves wrestling and baseball. His mother has taken him to the pediatrician because she is concerned about David's health. For the last four months, David has complained that his stomach hurts, he has had diarrhea on and off, and he often feels sick to his stomach. His abdomen is bloated and his mother mentions that he seems very irritable and tired. He has lost 6 pounds during the past four months and his mother is very concerned. The pediatrician suspects possible celiac disease, an autoimmune disorder in which the immune system attacks gluten. Gluten is a protein found in wheat, rye, and barley. The immune system produces antibodies that attack the lining of the small intestine and cause inflammation and damage. The pediatrician orders blood work, including tissue transglutaminase (tTG)-IgA antibodies (known as a tTG-IgA test), iron, and a complete blood count (CBC). David's tTG-IgA antibody test is positive (12 U/ml), and his iron levels are a little low. These tests are positive for possible celiac disease, but an endoscopic biopsy from the small intestine is ordered for confirmation.

How do enzymes initiate chemical reactions?

Enzymes are protein catalysts that lower activation energy.

Exercise 28 Review Sheet: Actions of a Digestive Enzyme

Enzymes are proteins that act as biological catalysts—substances that increase the rate at which chemical reactions occur. In this role, enzymes are essential for regulating all of the biochemical reactions in the cells of our bodies. Enzymes are precise in their actions. A particular enzyme will act only on a specific reactant substance, known as the substrate. The substrate binds to a particular region on the enzyme, called the active site, and forms the enzyme-substrate complex. The active site has a specific three-dimensional shape that is designed for binding only to the substrate. Once the enzyme-substrate complex has formed, the enzyme acts to accelerate the formation of a specific product. Subsequently, the newly formed product detaches from the active site. The enzyme is not changed, chemically, during the overall reaction and is recycled for repeated use. The reaction between an enzyme and a substrate can be summarized by the following sequence of events in the picture: Amylase, an enzyme found in saliva, initiates chemical digestion of starch in the oral cavity. Starch is a polysaccharide that contains repeating units of glucose. Amylase breaks down starch to maltose, a disaccharide consisting of two glucose molecules. To complete this Review Sheet, please complete the questions and activities below.

Pepsin is _______.

a peptidase, an enzyme that digests protein and a protein that digests protein

The purpose of this activity was to look at the effect of _______.

enzyme/substrate specificity