Questions and Answers
What is the formula for Vitamin A?
C20H30O
Which of the following nutrients is present in egg yolk but not in egg white?
The specific gravity of skimmed milk is higher than that of fresh milk.
True
What is the main protein found in milk that can be precipitated by acid?
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What is the enzyme involved in the breakdown of hydrogen peroxide into water and oxygen?
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Which of the following food samples tested positive for the presence of starch?
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To test for the presence of oil or fat in food samples, one should shake a small portion of the food with 3 mL of ___ in a test tube for several minutes.
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Retinoic Acid serves as an extracellular messenger.
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Match the food sample with the positive test result obtained: (Food Samples : Test Results)
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What enzyme is responsible for the darkening of exposed sliced fruits when exposed to air/oxygen?
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What enzyme catalyzes the decomposition of hydrogen peroxide to water and oxygen gas?
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Oxidases are enzymes that catalyze redox reactions and use ______ as electron acceptors.
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What happens to the catalytic effectiveness of enzymes when the potato extract is boiled?
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What is the cause of coagulation in the coagulation test?
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What causes the changes observed in Moore's test?
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To what class of protein does casein belong?
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What test involves the polymerization of aldehyde groups of sugars?
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What chemical is used for testing the presence of phosphorus?
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What is the Heller's Ring Test used for?
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Is bilirubin normally present in the urine?
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What does the presence of bilirubin in the urine indicate?
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What is the Benedict's Test used for?
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What is the Nitroprusside Test used for?
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What is the Benzidine Test used for?
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What is the Gmelin's Test used for?
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What is the purpose of Paper Chromatography?
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What is the formula for calculating the Rf value?
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What happens to salivary digestion after a 10-20 minute period?
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What is the relationship between pH and digestion for acids?
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What inorganic constituents are found in bile?
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What color does the litmus paper turn when tested with bile?
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Bile salts reduce the surface tension of the liquid, allowing stable foam formation when shaken.
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Hay's Test of Surface Tension Test is based on the principle that bile acids or bile salts have the property of reducing the ________ of the fluid.
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What is the difference between the pH of the resting saliva and the stimulated saliva?
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Is there any relation between the pH of the saliva and the susceptibility of dental caries?
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What is the precipitate formed when testing for mucin in saliva?
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What is the function of mucin in saliva?
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Which inorganic salt is found abundant in saliva?
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What is responsible for reducing the action in the Benedict's test?
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How long did it take for a complete transformation of starch into reducing sugar?
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How long does salivary digestion continue in the stomach?
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What is the danger of excessive amounts of cholesterol in the bile?
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What is the volume of the 24-hour urine?
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What substances are responsible for the normal color of urine?
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What happens when the urine is allowed to stand for some time, exposed to air?
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What is the specific gravity range of normal urine?
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What constituents of the urine tend to precipitate when the reaction is acidic?
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What is produced in the Sulphates detection test?
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What is produced in the Chloride detection test?
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What is the normal amount of chlorides eliminated in 24 hours?
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In what forms are chlorides in urine eliminated?
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Study Notes
Enzyme Activity
- Enzymes are complex organic compounds secreted by living cells that initiate and hasten chemical reactions without being affected themselves.
- Enzyme activity is influenced by:
- Concentration of the enzymes
- Concentration of the substrate
- Concentration of the products of the reaction
- Temperature
- pH
- Inorganic salts
- Presence of activators and inhibitors
Oxidases from Fruits
- Oxidases are enzymes that catalyze redox reactions and use oxygen as electron acceptors.
- Examples of oxidases include:
- Monophenol Oxidase (Tyrosinase): responsible for oxidizing phenol to catechol, to o-quinone and finally forms condensation brown compounds of unknown composition.
- Polyphenol Oxidase (Catechol Oxidase): acts on catechol to form o-quinone, then the unknown brown compounds.
- Cytochrome Oxidase: acts in conjunction with cytochrome, oxidizing phenylenediamine, which in the presence of alpha-naphthol forms indophenol.
Peroxidase from Potato
- Peroxidase is an enzyme that:
- Requires a co-factor, phenol-oxidase, to complete its action.
- Requires H2O2 as the source of oxygen, and upon which the phenol-oxidases act.
Catalase from Liver
- Catalase is an enzyme that:
- Catalyzes the decomposition of hydrogen peroxide to water and oxygen gas at a rate of 40 million molecules of hydrogen peroxide per second.
- Helps the liver filter the body by making harmful substances less toxic, such as hydrogen peroxide to water and oxygen, and alcohol to aldehyde.
Experiment 9: Test for Nutrients in Food
- The purpose of this experiment is to identify and understand the nutritional value with specific presence of organic molecules in foods.
Starch Test
- A deep blue color indicates the presence of starch in food samples.
Glucose Test
- A yellow to red precipitate indicates the presence of simple sugars such as glucose or fructose in food samples.
Carr-Price Test for Vitamin A
- A blue solution indicates the presence of Vitamin A in food samples.
Fat Test
- A translucent spot on white paper indicates the presence of oil or fat in food samples.
Cholesterol Test
- Cholesterol can be detected using microscopical examination, Acetic Anhydride–H2SO4 Test or Lieberman-Burchard Test, and Sulphuric Acid Test or Salkowski’s Test.
Protein Test
- A violet solution indicates the presence of proteins in food samples using the Biuret Test or Piotrowski’s Test.### Vitamin A
- Vitamin A (Retinol) is the immediate precursor to two important active metabolites: Retinol and Retinoic Acid
- Retinol plays a critical role in vision, while Retinoic Acid serves as an intracellular messenger that affects the transcription of a number of genes
- Vitamins A does not occur in plants, but many plants contain carotinoid (such as beta carotene) that can be converted to vitamin A within the intestine and other tissues
- Formula of Vitamin A: C20H30O
- Chemical structure: 3,7-dimethyl-9-(2,6,6-trimethylcyclohex-1-yl) nona-2,4,6,8-tetraen-1-ol
Importance of Vitamin A
- Vitamin A is essential for vision, growth, and maintenance of epithelial cells and mucous membranes
- Vitamin A deficiency can lead to night blindness, xerophthalmia, and impaired immune function
Experiment 11: Milk
Purpose
- To understand the reactions of milk, prepare casein, and the presence of organic materials in milk
Apparatus and Materials
- Test Tube, Test Tube Rack, Beaker, Funnel, Filter Paper, Bunsen Burner, Clay Flame Shield, Wire Gauze, Evaporating Dish, Vials, Litmus Papers (Blue & Red), Densimeter
- Fresh Milk, Diluted Canned Milk, Skimmed Milk, Congo Red, Phenolphthalein Solution, Acetic Acid, 6 M & Dilute Sodium Hydroxide, Ethyl Alcohol, Ether, etc.
Results and Observations
- Positive Result: Violet Solution with Egg White (Cooked), Egg Yolk (Cooked), Peanut Butter, Cheese, and Dilis
- Positive Result: White Powdery Residue with Cheese and Dilis
- Positive Result: Bluish-Red to Cherry Red and Purple with Chloroform (CHCl3) Layer and Marked Green Fluorescence with Sulfuric Acid (H2SO4) Layer
Importance of Milk
- Milk is a complete food that contains proteins, fats, carbohydrates, inorganic salts, and vitamins
- Fresh Unboiled Milk contains enzymes such as Protease, Lipase, Phosphatase, Catalase, and Peroxidase
- Casein is the chief protein of milk and can be precipitated by acid, carrying with it the milk fat
- Milk fat is believed to have its origin in the phospholipids of the blood
- Milk lactose is derived from the glucose of the blood
- Inorganic salts in milk include Calcium, Magnesium, Sodium, Phosphates, Citrates, and Chlorides
Determination of Specific Gravity
- Fresh Milk has a specific gravity of around 1.03
- Skimmed Milk has a specific gravity of around 1.04
- Milk fat is inversely proportional to specific gravity
Coagulation Test
- Coagulation of milk occurs due to the presence of whey protein, mainly composed of beta-lactoglobulin
- Coagulation can be induced by acidification with acetic acid and heat
Solubility of Casein
- Casein is insoluble in water and dilute HCl
- Casein is slightly soluble in 10% NaCl solution
- Casein is soluble in dilute NaOH solution
Moore's Test (Action of Hot Alkali)
- Moore's Test is used to detect the presence of reducing sugars like lactose
- The test involves mixing milk with 6 M NaOH and heating, resulting in the formation of caramel due to the reducing end of glucose
Millon's Test
- Millon's Test is used to detect the presence of tyrosine in casein
- The test involves adding Millon's reagent (1 Hg : 2 HNO3) to casein, resulting in a flocculent red precipitate formation
Preparation of Casein
- Casein can be prepared by acidifying milk with dilute acetic acid, followed by filtering and washing with ethyl alcohol and ether
- Casein is a heterogeneous group of four phosphoproteins and phosphoglycoproteins
Test for Presence of Phosphorus, Calcium, and Reducing Sugar
- The presence of phosphorus can be detected using conc. HNO3 and (NH4)2MoO4
- The presence of calcium can be detected using (NH4)2C2O4
- The presence of reducing sugar (lactose) can be detected using Benedict's Reagent### Whey
- Whey contains all other substances found in milk, apart from the separated casein, such as lactalbumin, lactoglobin proteins, phosphorus, calcium, and lactose.
- Tests for whey components:
- Phosphorus: yellow ppt. of ammonium phosphomolybdate
- Calcium: white ppt. of calcium oxalate
- Lactose: orange ppt. of cuprous oxide (Benedict's)
- Coagulation by heating: forms a coagulum consisting of lactalbumin and lactoglobin
- Biuret test: violet solution (+)
Milk Fat
- Milk fat is the residue left after evaporating the ether from the filtrate obtained in no. 6
- Milk fat forms a translucent spot when touched with a piece of paper
Salivary Digestion
- Purpose: to understand the reactions of saliva and stimulate salivary digestion
- Saliva:
- Secreted by 3 pairs of glands and hundreds of small buccal glands
- Contains protein (mucin), enzyme (ptyalin), and inorganic salts
- Flow is stimulated by psychic, chemical, and mechanical factors
- Salivary digestion:
- Hydrolysis of starch by salivary amylase (ptyalin)
- Takes place in the buccal cavity and to a certain extent in the fundic end of the stomach
- pH of saliva:
- Resting saliva: slightly basic (pH = 6.2-7.6)
- Stimulated saliva: more basic (pH = 7.0-8.0)
- Relation between pH of saliva and susceptibility to dental caries:
- Acidic pH is essential in enamel dissolution to produce dental caries
- Tests on saliva:
- Test for chloride: turbid white ppt. (AgCl)
- Test for phosphate: clear, colorless ppt. (NH4)3PO4 12MoO3
- Test for sulfate: slightly turbid ppt. (BaSO4)
- Test for calcium: clear, colorless ppt. (CaC2O4)
Starch Digestion
- Ptyalin is responsible for starch digestion
- Stages of starch digestion by ptyalin:
- Boiled starch + ptyalin = soluble starch
- Soluble starch + ptyalin = erythrodextrin + maltose
- Erythrodextrin + maltose + ptyalin = achrodextrin + maltose
- Achrodextrin + maltose + ptyalin = isomaltose + maltose
- Difference between starch acid hydrolysis and starch digestion by ptyalin:
- Starch acid hydrolysis is a nonspecific chemical reaction requiring harsh conditions to achieve complete breakdown of starch into glucose
- Starch digestion by ptyalin is an enzymatic, specific, and controlled process occurring under physiological conditions
- Influence of acid and alkali on starch digestion:
- Acid: disrupts the basicity of saliva, necessary for buffering capacity
- Alkali: ↑ concentration/alkalinity = ↑ digestion
- Effect of gastric juice on salivary digestion:
- Gastric juice starts protein digestion and inhibits salivary digestion
- Salivary digestion continues in the stomach for 10-20 minutes due to the slow penetration of acidic gastric juice into the bolus
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Observe how enzymes react with sliced fruits, leading to darkening. Analyze the reactions and understand enzyme activity.