Analysis and Denaturation of Proteins

Question 1

function as biological catalysts or enzymes, transporter of oxygen and hormone

Answer 1

proteins

Question 2

repeating unit of protein

Answer 2

amino acid

Question 3

4 levels of protein structure

Answer 3

1. Primary structure
2. Secondary structure
3. Tertiary structure
4. Quaternary structure

Question 4

composed of single covalently bonded amino acid

Answer 4

primary structure

Question 5

two types of secondary structure

Answer 5

alpha helix structure
beta-sheet structure

Question 6

contains one strand of amino acid chain that is bonded by intramolecular hydrogen bond

Answer 6

alpha helix structure

Question 7

two chains that are linked by hydrogen bonds

Answer 7

beta-sheet structure

Question 8

combination of pure helix or pure beta, or a combination of both

Answer 8

tertiary structure

Question 9

stabilizing interactions in tertiary level

Answer 9

1. salt linkages
2. hydrophobic interactions
3. disulfide linkages
4. hydrogen bonds

Question 10

interaction of two or more folded polypeptides

Answer 10

quaternary structure

Question 11

is the unfolding of complex secondary, tertiary, and quaternary structure of protein

Answer 11

denaturation

Question 12

what can denature proteins?

Answer 12

1. heat
2. strong acid
3. organic solvents/acids
4. heavy metals

Question 13

it causes the atom within the protein molecule to vibrate more rapidly, causing the hydrogen bonds and hydrophobic interactions to break.

Answer 13

heat

Question 14

they split salt linkages by ionizing the caboxylic group

Answer 14

strong acids

Question 15

it denatures the protein by disrupting the hydrogen bonds

Answer 15

alcohol

Question 16

they denature proteins by combining the carboxylate anions of the acidic amino acid with the metal, causing precipitation

Answer 16

heavy metal ions (silver, lead, mercury)

Question 17

are used to precipitate alkaloids, giving “alkaloidal reagents”

Answer 17

organic acids like picric acid and tannic acid

Question 18

the anion of these acids will react to the protonated amino acid group of protein, causing the disruption of salt linkages

Answer 18

organic acids ( picric acid and tannic acid)

Question 19

Color Tests of Protein

Answer 19

1. Biuret Test (2 mL 10% NaOH + 5 drops CuSO4)
2. Ninhydrin Test
3. Xanthoproteic Test
4. Millon’s Test
5. Hopkin’s Cole Test
6. Sakaguchi Test
7. Lead Acetate Test (Test for Sulfur)

Question 20

Positive result for compounds that contain two or more peptide linkages

Answer 20

Biuret Test

Question 21

Color of biuret test

Answer 21

purple (due to complex by cupric ions)

Question 22

dipeptides and amino acids that do not give positive result to BT

Answer 22

serine, threonine

Question 23

when amino acids are sprayed w/ ninhydrin, it will give

Answer 23

blue to violet

Question 24

the presence of amino group including amine and ammonia will give positive result in NT except

Answer 24

proline & hydroxyproline (yellow)

Question 25

in XT, nitration of amino acids that contain benzene ring will yield the product of ____ that will give color

Answer 25

nitrobenze, yellow to orange

Question 26

in XT, they will produce nitrobenzene when treated w/ concentrated nitric acid

Answer 26

1. tryptophan 2. phenylalanine 3. tyrosine

Question 27

in XT, what do not give a positive reaction

Answer 27

collagen and gelatin

Question 28

in MT, the phenol group in amino acid like tyrosine is nitrated by a solution of ___ in concentrated nitric acid

Answer 28

mercuric and mercurous nitrates

Question 29

what will be formed in millon's test

Answer 29

white precipitate, turning brick red (due to mercury complex)

Question 30

in MT, addition of ____ will turn the precipitate to

Answer 30

NaNO2, darker pink or red

Question 31

color of precipitate in MT

Answer 31

white - brick red (due to mercury complex - darker pink/red (upon addition of NaNO2

Question 32

BT is for

Answer 32

two or more peptide linkages

Question 33

XT is for

Answer 33

amino acids that contain benzene ring

Question 34

Ninhydrin is for

Answer 34

amino group

Question 35

MT is for

Answer 35

phenol group (ex. tyrosine)

Question 36

HT is for

Answer 36

aldehyde

Question 37

in HT, the aldehyde present in reagent will cause the formation of a

Answer 37

blue or violet colored ring (due to formation of a complex bet. reagent and indole ring

Question 38

ST is to identify the presence of

Answer 38

arginine

Question 39

in ST, sodium hypobromite or hypochlorite react with guanido group giving a

Answer 39

red-orange colored complex

Question 40

This is a test for sulfur-containing amino acids like cysteine and methionine

Answer 40

Lead Acetate Test

Question 41

The sulfahydryl or disulfide group are converted to

Answer 41

Na2S (inorganic sulfide)

Question 42

Na2S reacts with lead acetate to form

Answer 42

brownish-black precipitate of lead sulfide (Pbs)

Question 43

Xanthoproteic Procedure

Answer 43

reagents: HNO3, NH4OH albumin - yellow, richer yellow gelatin - no reaction casein - pale yellow, richer yellow

Question 44

Millon's Procedure

Answer 44

reagents: millon's reagent, 0.1% NaOH albumin - red, yellow-orange gelatin - no reaction casein - red, yellow-orange

Question 45

HCT Procedure

Answer 45

reagents: HCT reagent, sulfuric acid albumin - blue ring below the albumin gelatin - no reaction casein - blue ring below the milk

Question 46

Lead Acetate Procedure

Answer 46

reagents: 5 drops 10% NaOH, 3 drops 5% Lead acetate albumin - black precipitate (Pbs) gelatin - no precipitate

Question 47

NT Procedure

Answer 47

reagents: Ninhydrin albumin - dark violet top, white bottom gelatin - no reaction casein - violet

Question 48

Biuret Procedure

Answer 48

reagents: 10% NaOH, 5 drops CuSO4 albumin - slightly cloudy, dark purple gelatin - orange to red casein - purple

Question 49

Heat

Answer 49

albumin + 3 mL water + boiling water bath: after cooling = cloudy color: purple/violet (peptide bond)

Question 50

Heat

Answer 50

albumin + 3 mL water - violet

Question 51

Inorganic Acids

Answer 51

3 mL 5% albumin + HCL = precipitate at 8th drop 3 mL 5% albumin + H2SO4 = precipitate at 8th drop, increased 2 drops

Question 52

Alcohol

Answer 52

reagents: 5 mL 95% ethanol albumin - no precipitate, albumin became opaque gelatin - no precipitate formed casein - white precipitate

Question 53

Heavy Metals

Answer 53

reagents: egg albumin lead acetate - black precipitate silver nitrate - white precipitate mercuric chloride - cloudy or white