biochemistry pre test lab experiment 4

Question 1

3 kinds of proteins in milk

Answer 1

casein, lactalbumin, lactoglobulin

Question 2

What is the most nutritionally complete food found in nature

Answer 2

milk

Question 3

_______ is the main protein in milk. It is a phosphoprotein

Answer 3

casein

Question 4

3 similar proteins in milk

Answer 4

β-casein, α-casein, κ-casein

Question 5

__-casein and __-casein are both insoluble in water

Answer 5

β-casein, α-casein

Question 6

__-casein is responsible for solubilizing the other two casein in water by promoting the formation of micelles.

Answer 6

κ-casein

Question 7

Casein exists in milk as the calcium salt, _________ ________

Answer 7

calcium caseinate

Question 8

Calcium caseinate has an isoelectric point of pH ____.

Answer 8

4.6

Question 9

The pH of milk is about ____

Answer 9

6.6

Question 10

second most abundant protein in milk is __________

Answer 10

lactalbumin

Question 11

________ carries out the immunological properties of milk. They protect the younger mammal until its immune system has developed

Answer 11

lactoglobulins

Question 12

EXTRACTION OF CASEIN:
1. Measure 30 mL of nonfat milk and place it in a 100-mL beaker. Add 30 mL of distilled water. Heat on a hot plate to about 1___°C (top of the hot plate at about 2___°C). Monitor the temperature of the milk using a thermometer.

Answer 12

1- 55°C, 2- 65°C

Question 13

EXTRACTION OF CASEIN:
2. When the mixture has reached 55°C, add the ____ ______ _____ dropwise to the warm
milk with stirring using a glass rod. Do not add the acid too rapidly. Continue the acid
addition, keep the beaker on the hot plate until the liquid changes from milky to
almost clear, and the casein no longer separates (No more than 2 mL of the acid is
needed).

Answer 13

10% acetic acid

Question 14

EXTRACTION OF CASEIN:
3. Stand the mixture for __ minutes.

Answer 14

5

Question 15

EXTRACTION OF CASEIN:
4. Stir the precipitated casein until it forms a large ___________ ______; then remove it with a stirring rod or tongs (or by filtration) and place it in another beaker. Label the beaker “casein”.

Answer 15

amorphous mass

Question 16

EXTRACTION OF CASEIN:
5. Keep the filtrate (______ _______) for PART III.

Answer 16

whey solution

Question 17

EXTRACTION OF CASEIN:
6. Place the obtained casein in a 100 mL beaker and add 5 mL of a mixture of : _____ _____ and ________. Stir the casein in the mixture for a few minutes, decant the liquid, and repeat the process with a second 5 mL portion of the solvent. These washings remove any small quantities of fat that may have precipitated with the casein. Place the casein between several layers of filter paper to help dry the product, and let it stand in the air for 10-15 minutes.

Answer 17

1- 1:1 ethyl ether, 2- ethanol

Question 18

7. Divide the extracted casein into two. Place one portion in an Erlenmeyer flask with ___ mL of _______ and ____ mL of ___ ______, stopper the mixture, shake it to ensure solution of as much of the casein as possible, and save it for use in the chemical tests below. The other portion is for observation of its physical properties. Record the physical appearance of casein in Table 1.

Answer 18

35 mL of water and 0.5 mL of 1M NaOH

Question 19

The 1______ Test is a general test for the presence of proteins, which is dependent on the presence of peptide bonds.

Answer 19

Buiret Test, Piotrowskis test

Question 20

A positive result for the Buiret Test or Piotrowskis test

Answer 20

Violet color, if it contains peptides, proteoses, and peptones, a minimum of 2 peptide bonds

Question 21

reagents of the biuret test

Answer 21

CuSO4 and NaOH

Question 22

_______ test is a general test for the presence of proteins, which is dependent on the presence of free alpha amino groups.

Answer 22

Ninhydrin test

Question 23

reagents of the Ninhydrin test

Answer 23

0.1 Ninhydrin solution

Question 24

A positive result for the Ninhydrin test

Answer 24

Presence of diketohydrin, a color complex that is also known as Ruhemans purple. (Deep blue or violet color)

Question 25

The __________ test is used to indicate the presence of amino acids containing phenyl (benzene ring), namely phenylalanine, tyrosine, and tryptophan

Answer 25

Xanthoproteic test

Question 26

reagents of the Xanthoproteic test

Answer 26

HNO3 and ammonia NH3

Question 27

A positive result for the Xanthoproteic test

Answer 27

(Yellow to orange color)

Question 28

________ reaction is a specific test for the presence of the amino acid tryptophan

Answer 28

Adamkiewicz reaction

Question 29

A positive result for the Adamkiewicz reaction

Answer 29

Formation of violet ring

Question 30

___________ test is a general test for the presence of carbohydrates in a solution

Answer 30

molisch’s test

Question 31

reagents of the molisch’s test

Answer 31

Molishs reagent and sulfuric acid (concentrated H2SO4)

Question 32

_________ test is a test for phosphate in the solution.

Answer 32

Phosphate test

Question 33

reagents of the Phosphate test

Answer 33

Concentrated HNO3 and 0.2M ammonium molybdate

Question 34

Tests for characterization of protein

Answer 34

Biuret Test, Ninhydrin Test, Xanthoproteic test, Adamkiewicz Test, Molischs test, and Phosphate test

Question 35

Test for other nutrients in milk

Answer 35

Test for lactose, test for calcium, Test for chlorides, and test for sulfates

Question 36

reagents of the Test for lactose

Answer 36

Benedicts reagent

Question 37

A positive result for the Test for lactose

Answer 37

Formation of a brick-red precipitate

Question 38

reagents of the test for calcium

Answer 38

Potassium Oxalate (K2C2O4)

Question 39

A positive result for the test for calcium

Answer 39

A white precipitate of calcium oxalate (CaC2O4)

Question 40

reagents of the test Test for chlorides

Answer 40

Silver Nitrate (AgNO3)

Question 41

A positive result for the Test for chlorides

Answer 41

A white precipitate of silver chloride (AgCl)

Question 42

reagents of the test Test for sulfates

Answer 42

Barium Chloride (BaCl2)

Question 43

A positive result for the Test for sulfates

Answer 43

A white precipitate of barium sulfate (BaSO4)