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1 Enzymes Flashcards

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1
Q

what methods can you use to prove that enzymes are protein in nature?

A

chemical hydrolysis
enzyme hydrolysis
conventional protein assays
x-ray crystallography

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2
Q

how does chemical hydrolysis prove that enzymes are protein in nature?

A

enzyme interacts with H+ or OH- (acids/bases); broken down into peptides and amino acids

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3
Q

how does enzyme hydrolysis prove that enzymes are protein in nature?

A

enzymes react to proteases/proteolytic enzymes; broken down into peptides and amino acids

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4
Q

what are some conventional protein assays and what happens?

A
  • Lowry method: protein reacts to Cu ions. aromatic residues are oxidated and the solution turns blue
  • ninhydrin method: detects ammonia or primary/secondary amines. turns purple
  • Folin-phenol method: reacts with any reducing substance
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5
Q

how does x-ray crystallography prove enzymes are protein in nature?

A

shows composition of amino acids linked by peptide bonds

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6
Q

what is the term for an functional/active compound that consists of either just an apoenzyme or an apoenzyme & an essential prosthetic group?

A

holoenzyme

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7
Q

what’s an apoenzyme?

A

the protein part of the enzyme

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8
Q

what’s a prosthetic group?

A

non-protein part. aka co-factor

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9
Q

list some enzymes that lack a prosthetic group

A

trypsin, chymotrypsin, pepsin

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10
Q

list some enzymes that are comprised of both an apoenzyme and prosthetic group

A

PPO (polyphenol oxidase), xanthine oxidase

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11
Q

define enzyme active site

A

location on enzyme where catalysis occurs (substrates to products)

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12
Q

what is catalysis? what are the 2 steps?

A

the facilitation of a reaction. bonds may be formed or existing bonds may be broken.

2 steps are: 1) binding of substrate 2) transformation of substrate to product

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13
Q

what happens if there is binding of a substrate, but no transformation?

A

not catalysis lol

an example of this is when an inhibitor binds instead of a substrate

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14
Q

describe the active site

A

3d entity. shaped like pockets and crevices. small (duh)

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15
Q

what’s the significance of enzyme specificity?

A

enables consistent formation of products without the formation of undesirable co-products

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16
Q

define absolute specificity and give examples of enzymes with this trait

A

very stringent in what they select

ex) glucose oxidase, glucokinase, catalase

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17
Q

define group specificity and give examples of enzymes with this trait

A

sects a group of closely related molecules to transform

ex) hexokinase, lipase, proteases

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18
Q

what is stereospecificity (with regard to enzymes)?

A

when a reaction selects one stereoisomer to transform (cis/trans)

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19
Q

distinguish between racemases and epimerases

A

racemases catalyze inversion around an achiral carbon with only ONE achiral center

epimerases do that, but with more than one achiral center.

if there are >1 achiral centers, it can still be an enantiomer if and only if all of the centers have been mirrored.

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20
Q

why do we purify enzymes?

A

to remove interfering compounds, silly

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21
Q

what characteristics of enzymes can be manipulated during purification

A
  • size
  • solubility
  • charge
  • selective adsorption
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22
Q

what are four size based purification techniques?

A
  • dialysis
  • ultrafiltration
  • centrifugation
  • gel filtration
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23
Q

what happens during dialysis?

A

particles small enough to pass through the semi-permeable membrane move down concentration gradients until equilibrium is achieved. this means that you can’t isolate 100% of a sample using this method

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24
Q

what happens during ultrafiltration?

A

pressure is applied to a membrane. more efficient than dialysis

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25
Q

what happens during centrifugation?

A

the sample has the devil spun out of it. also the larger particles settle at the bottom first

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26
Q

what happens during gel filtration?

A

small resins (tubes) are put in a gel. smaller molecules get stuck in the tubes and filter out after larger ones. (aka bigger comes out first)

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27
Q

what are three charge based separation techniques?

A
  • ion exchange chromatography
  • Electrophoresis
  • isoelectric focusing
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28
Q

which separation technique involves the use of charged resins?

A

Ion exchange chromatography

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29
Q

define strong/weak cation/anion exchangers

A

strong - charges on resins stable over wide pH range
weak - small pH range

cation - attracts cations (negatively charged resin)
anion - attracts anions (positively charged resins)

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30
Q

sulfonic acid is a…

A

strong cation exchanger

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31
Q

quaternary ammonium is a…

A

strong anion exchanger

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32
Q

carboxy methyl cellulose is a…

A

weak cation exchanger

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33
Q

diethylaminoethane (DEAE) is a…

A

weak anion exchanger

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34
Q

the technique involving the migration/mobility of charged molecules under the influence of a current in an electric field is called:

A

Electrophoresis

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35
Q

what 2 factors does migration/mobility depend on?

A

charge (q) - proportional

size (r) - inversely proportional to square of radius

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36
Q

what’s lauryl sulfate do?

A

imparts equalizing large net charge on different molecules. after treatment, electrophoresis, they will separate based on size.

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37
Q

the technique in which molecules migrate through a pH gradient until they reach their isoelectric point is:

A

isoelectric focusing (or electric focusing)

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38
Q

what’s chromatographic focusing?

A

molecules move through pH gradient until they reach their isoelectric point, but within a column

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39
Q

larger enzymes are (more/less) soluble than smaller ones?

A

less

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40
Q

molecules with hydrophobic chains are (more/less) soluble in aqueous solvents

A

less

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41
Q

what’s significant about the amino acids: phenylalanine, valine, leucine, and isoleucine?

A

they all contain hydrophobic side chains

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42
Q

molecules with hydrophilic side chains are (more/less) soluble in aqueous solvents

A

more

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43
Q

what’s significant about the amino acids: serine, glutamic acid, aspartic acid, and threonine?

A

they all contain hydrophilic side chains

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44
Q

what is salting in?

A

increasing the ionic strength of a solution increases the solubility of a solute (lower concentrations of salt)

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45
Q

what is salting out?

A

high concentrations of salt, the solubility of the proteins drop sharply and proteins can precipitate out

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46
Q

what are three separation techniques based on solubility differences?

A
  • isoelectric precipitation
  • salt fractionation
  • solvent precipitation
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47
Q

the technique involving bringing a solution to a protein’s isoelectric point to decrease its solubility and make it precipitate:

A

isoelectric precipitation

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48
Q

what’s salt fractionation? why does it work?

A

the very same thing as salting out babeyy

imparts charge onto protein and limits water available to dissolve it

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49
Q

the technique involving the use of organic solvents to precipitate proteins is:

A

solvent precipitation

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50
Q

how does solvent precipitation work?

A

the solvent strips the thin film of moisture normally present on the enzyme and disrupts the enzyme’s activities

do this at 4°C and neutral pH to avoid inactivation.

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51
Q

what’s a good salt to use for separation purposes?

A

ammonium sulfate

52
Q

what are good solvents for solvent precipitation?

A

acetone (preferred), ethanol

53
Q

what are 2 binding site based separation techniques?

A
  • affinity chromatography

- hydrophobic interaction chromatography (HIC)

54
Q

the technique involving the placement of ligands in a column to limit the movement of the enzyme of interest is:

A

affinity chromatography

55
Q

the technique involving the use of hydrophobic resins on which to stick the hydrophobic enzymes is called

A

hydrophobic interaction chromatography

56
Q

what are 4 things you can do to test for enzyme purity?

A
  • homogeneity (presence of a single band in electrophoresis)
  • chromatography behavior (graph absorbance vs fraction #: pure curve will be bell shaped)
  • activity testing
  • isoelectric focus
57
Q

name the enzyme groups in order

A

1) Oxidoreductase
2) Transferase
3) Hydrolase
4) Lyase
5) Isomerase
6) Ligase

58
Q

what group of enzymes catalyze redox reactions? what are some examples?

A

Group 1 - Oxidoreductases

PPO, GOX (removes sweetness and oxygen from egg white and powdered milk), DOPA, Xanthine

59
Q

what group of enzymes catalzye the transfer of groups from one molecule to another? what are some examples?

A

Group 2 - transferases

transglutaminase (TGase): transfers groups between gamma-carboxamide residue of glutamine to epsilon-NH2 group of lysine, liberating ammonia and forming an isopeptide bond (C=O)-NH-lys. makes molecules bigger. used to prepare consolidated meats, or to firm up soft fish flesh in surimi.

60
Q

1) what groups get transferred by TGase?

2) what molecules does TGase transfer groups between?

A

1) γ-carboxamide and ε-NH2

2) glutamine and lysine respectively

61
Q

what group of enzymes break down larger molecules into smaller ones using WATER as a CO-REACTANT? examples?

A

Group 3 - Hydrolases

ex) proteolytic enzymes, amylases, lipases

62
Q

what’s the most important group of enzymes in the food industry?

A

group 3

63
Q

what group of enzymes break or create DOUBLE BONDS?

A

Group 4 - Lyases

ex) fumarase (removes db), histidine decarboxylase

64
Q

what group of enzyme does aldolase belong to?

A

lyase. it cleaves fructose-1,6-bisphosphate into G3P and DHAP, forming a double bond

65
Q

what group of enzymes converts molecules into isomers? examples?

A

Group 5 - isomerases

ex) glucose isomerase (converts glucose to fructose)

66
Q

what group of enzymes put smaller molecules together to make larger ones? examples?

A

group 6 - Ligases

ex) stringing together of nucleotides, carboxylase (formation of oxaloacetate using pyruvate and CO2)

67
Q

by what mechanism does enzyme catalysis occur?

A

enzymes decrease the activation energy of a reaction.

68
Q 
ΔG = ?
ΔH¢ = ?
ΔS = ?
R = ?
Ea = ?
A 
ΔG = change in free energy of activation
ΔH¢ = change in enthalpy
ΔS = change in entropy
R = universal gas constant
Ea = activation energy
69
Q

you can increase rate of catalysis by (increasing/decreasing) concentration of enzyme and (increasing/decreasing) concentration of substrate

A

increase, increase

70
Q

rate Rx depends on what parts of the enzyme reaction?

A

[E], [S], T, stability of ES, [p], pH

71
Q

how do you measure Rx rates?

A
  • appearance of P

- disappearance of S

72
Q

what two methods of measurements can you use to determine Rx rate

A
  • initial rate method (take measurements immediately after zero time; true measurement bc no inhibitory products yet)
  • end-point method (take measurements after a set amount of time after zero time; no expensive equipment or skill required)
73
Q

what are the 3 stages of enzymatic activity curve?

A

pre-steady state, steady state, post steady state

74
Q

state where curve appears exponentially shaped

A

pre-steady state

75
Q

state where curve appears linear

A

steady state

76
Q

state where curve appears like a horizontal line

A

post steady steady state

77
Q

what are K1, K2, and K3?

A 
K1 = putting together of E and S
K2 = dissociation of ES back to E+S
K3 = formation of E + P from ES
78
Q

K1 = K2 + K3

what does this mean?

A

ES is breaking down at the same rate it is formed

79
Q

in what state are catalytic measurements usually taken?

A

steady state

80
Q

V0 = ?

A

initial/observed velocity

1/2 Vmax

81
Q

how do you find vmax?

A

stick a tangent line approximately where the leveling off of the curve is and then read where it intersects with the y axis

82
Q

Km = ?

A

ratio of breakdown of complex to formation (K3+K2)/K1 - represents affinity of E for S

numerically equal to [S] when: V0=1/2Vmax

83
Q

how useful is the michaelis-menten plot?

A

not useful in practice because there is no true levelling off of the curve. it actually keeps going up, so you don’t get a tru Vmax or Km

instead we use lineweaver-burke method

84
Q

what does the lineweaver-burke plot look like?

A

linear

85
Q

what is the slope and intercept of the lineweaver-burke plot?

A

slope: Km’/Vmax
int: 1/Vmax

86
Q

what does Vmax signify?

A

ease of catalysis

87
Q

what signifies catalytic efficiency?

A

Vmax/Km’ ratio

higher ratios = more economical

88
Q

what do enzyme inhibitors do?

A

minimize activity/reduce rates of enzyme catalysis

89
Q

what are the 3 types of reversible inhibition?

A

1) competitive
2) non-competitive
3) uncompetitive

90
Q

when “I” binds to active site, this is ___ inhibition

A

competitive

91
Q

when “i” binds not at active site and prevents transformation of S to P, this is ___ inhibition

A

noncompetitive

92
Q

when “i” binds to site on “E” that becomes available only after “S” has bound to active site (i.e. to the ES complex), this is ___ inhibition

A

uncompetitive

93
Q

benefits of enzymes in food processing?

A
  • viewed as natural
  • specific
  • don’t need high concentrations
  • no need for expensive and corrosive equipment
  • easy to stop enzyme action with mild heat treatment
  • easy removal
94
Q

what enzymes are involved in cheese making?

A

rennin/rennet, pepsins/chymosins

peptide binds calcium ions, bringing other caseins together to form curd

95
Q

how are proteases used in the beer industry?

A

if you don’t use proteases to break down proteins, then at a low temp you will find sediments at the bottom. the proteases keep peptides in solution. this is called *chill proofing)

96
Q

what use are amylases in baking?

A

break down starches into simple sugars so that yeast can eat it and release CO2, allowing loaves to swell

97
Q

what use are proteases in baking?

A

modify proteins like gluten to make the product more pliable

98
Q

what use are lipoxidases in baking?

A

bleaches flour by breaking down carotenoids

99
Q

what is TGase used for????

A

slapping together of meat scraps into a larger hunk o’meat

100
Q

what are lipases used for in the meat industry?

A

flavors

101
Q

what are proteases used for in the meat industry?

A

texture, solubilization

102
Q

what are the primary reactions in foods catalyzed by enzymes? (4)

A
  • protease
  • carbohydrase
  • lipase
  • oxidoreductase
103
Q

what 2 types of proteases are there/?

A

1) endoproteases - act randomly

2) exoproteases - act at end of protein molecules

104
Q

what subgroups do exoproteases attack?

A

amino peptidase and carboxy peptidase

105
Q

what are endoproteases used for?

A

converting proteins from solid to liquid (you want extensive breakdown for small liquified molecules)

106
Q

what are exoproteases used for?

A

debittering agents. done by removing amino acid from the terminals of proteins

107
Q

generally speaking, action of lipases is (desirable/undesirable). why?

A

undesirable. FFAs formed are less stable than the acyl glycerides and are responsible for rancid odors

108
Q

when is lipolysis desirable?

A

characteristic flavors of certain food products like buttermilk, roquefort, milk chocolate, margarines, baked goods, coffee whiteners, imitation dairy products, soups, pizza)

109
Q

what are 7 important group 1 enzymes?

A
  • ascorbic acid oxidase
  • PPO
  • glucose oxidase (GOX)
  • catalase
  • lipoxygenase (lipoxidase)
  • xanthine oxidase
  • peroxidase
110
Q

what properties are enzymes good for modifying?

A
  • solubility
  • functional properties
  • flavor
111
Q

what is bitterness due to?

A

hydrophobic amino acids at terminal ends of proteins

112
Q

significance of whey and proteases?

A 
whey has a lot of good proteins:
- lactalbumins
- lactoglobulins
- albumin
- immunoglobulin
proteases hydrolyze them into hydrolysates which are less allergenic than the unhydrolyzed versions
113
Q

how do can proteases help with Celiac’s?

A

can hydrolyze wheat proteins to break down gluten to form peptides and hydrolysates that can be used for food flavorants

114
Q

how are proteases used in the making of alcoholic beverages?

A

flavor development

115
Q

how do enzymes contribute to dental care?

A

plaque is comprised of mouth bacteria, dextrins/sugars and glycoproteins.

  • lysozymes break down bacteria cell walls
  • dextranases break down sugars
  • proteases break down glycoproteins
116
Q

how do enzymes get rid of hair?

A

hair contains keratin proteins. use keratinase to break it down, but don’t leave it too long on the skin or else you can irritate your skin

117
Q

how do enzymes improve tea solubility?

A

tannins in tea are large, insoluble molecules. tannases break them down into them down to make them more soluble in cold teas

118
Q

do you experience more flavor when a beverage is hot or cold?

A

warm. molecules move faster and interact with taste receptors more

119
Q

how do enzymes help with the preparation of sturgeon roe?

A

there’s a membrane that must be removed. traditionally, eggs are shaken over a screen, but this has high losses.

enzymes increase yields

120
Q

how do enzymes help with the deskinning/descaling of fish

A

use macerating enzymes to cause less cut damage in fish fillets

121
Q

temperature based control methods

A

blanching, freezing, chilling, pasteurization

122
Q

water activity based control methods

A

salting, dehydration

123
Q

chemical based control methods

A

sulfites, acids, alkalis, antioxidants, chelating agents

124
Q

what are some novel methods of enzymatic control?

A
  • high pressure treatment processing
  • enzyme treatment using killer enzymes/anti-enzymes
  • inhibitors
  • chemical modification
  • ionizing radiation
125
Q

how does high pressure treatment work?

A

causes compaction in molecule. the change in volume is enough to change the configuration of the enzyme and causes a loss in activity

126
Q

what is one thing you can do for chemical modification?

A

attach alcohols to essential residues

127
Q

how does ionizing radiation work?

A

causes formation of free radicals that can polymerize causing a reduction in enzyme activity

food chem 2 (5 decks)

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