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Food Chemistry 2 > Enzymes > Flashcards

Enzymes Flashcards

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1
Q

What are functions of enzymes?

A
  • reduces activation energy

- enables biological rections to proceed at faster rates

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2
Q

properties of enzymes?

A
  • enzymes can be hydrolyzed by dilute acids or alkali to form free AA or low molecular weight peptides
  • E can be broken down by proteases to form AA or peptides with participation of H2O
  • E can respond to typical common protein tests (ie. ninhydrin and lowry)
  • E is comprised of AA linked together by peptide bonds
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3
Q

what can hydrolyze enzymes?

what do they form?

A

dilute acids or alkali; or peptides

forms free AA or low molecular weight peptides

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4
Q

what links AAs together?

A

peptide bonds

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5
Q

sizes of collagen, myosin, trypsin, amylose?

A

collage: 100-400kDa
myosin: 200kDa
trypsin: 20kDa
amylose: 40-50kDa

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6
Q

def of proenzyme?

A

immature and inactive enzyme

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7
Q

def of holoenzyme?

A

complete enzyme that is active

it is bound to its cofactor

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8
Q

def of apoenzyme?

A

enzyme that requires a cofactor

it is inactive

becomes active when it is bound to a cofactor

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9
Q

def of a prosthetic group?

A

the non-protein part that forms a part of a protein

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10
Q

examples of prosthetic groups?

A

metal ions: Ca, Fe, Zn

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11
Q

relationship between holoenzyme and prosthetic group?

A
  • sometimes, the holoenzyme is the whole protein
  • other times, the holoenzyme needs the essential non-protein part for the protein to be active (ie. the prosthetic group)
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12
Q

what are features of the enzyme active site? (3)

A

small
3D
clefts/crevices

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13
Q

what are 2 events that occur at the active site?

A

binding and transformation

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14
Q

Relationship between binding and transformation?

A
  • binding of substrate preceeds transformation
  • not all binding leads to transformation
  • no transformation occurs without binding
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15
Q

4 levels of enzyme specificity?

A
  1. bond specificity
  2. group specificity
  3. absolute specificity
  4. sterospecificity
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16
Q

how are enzymes bond specific?

A
  • E acts on compounds with one type of bond (ie. lipase can act on lipids as long as they have an ester bond)
  • can have relative or low specificity
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17
Q

How are enzymes group specific?

A

when an enzyme acts on a group of closely related compounds

  • ie. pepsin can hydrolyze peptide bonds where there is are aromatic AAs
  • ie trypsin can hydrolyze peptide bonds where there are basic AA
  • moderate specificity
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18
Q

how are enzymes absolutely specific?

A

when enzyme acts on one single substrate

  • ie lactase only acts on lactose. Sucrase only acts on sucrose
  • very high specificity
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19
Q

how are enzymes sterospecific?

A

when enzyme acts on one isomer of a molecule

-ie L-AA oxidase acts only on L-AA

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20
Q

why is it necessary to understand specificity in a baking company?

A
  • linear starch has alpha(1-4) bonds.
  • branched starch has alpha (1-6) bonds
  • linear starch is stickier than branched starch
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21
Q

how many enzyme classifications are there? what are these classifications based on?

A

6 classifications

based on recommendation of enzyme commission of the international union of biochemists

also based on types of reaction catalyzed

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22
Q

what is the numbering system that enzyme nomenclature

A

enzyme commission = EC

EC = (A.B.C.D) –> letters are digits

A = 1st group
B = sub group
C = sub sub group
D = numbering
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23
Q

what are the 6 enzyme classifications?

A
  1. oxidoreductase
  2. transferase
  3. hydrolyse
  4. lyases
  5. isomerases
  6. ligases
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24
Q

what are oxidoreductases?

A

can catalyze oxidation or reduction reactions

ie. polyphenol oxidase (PPO), glycose odidase (GOX), peroxidase, lipoxygenase

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25
Q

what are transferases

A

transfers groups from one substrate (the donor) to another substrate (Acceptor)

eg. transglutaminase

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26
Q

what are hydrolyases

A

catalyzes cleavage or hydrolysis of larger molecules into smaller molecules with H2O as a co-reactant

eg. proteases and lipases

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27
Q

what are lyases

A

removes group from one molecule, leaving behind a product with a lower molecular weight (usually with unsaturated bonds)

eg. histidine decarboxylase, pectin, lyase

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28
Q

what are isomerases

A

catalyzes the conversion of molecules into their isomers

eg. glucose isomerase

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29
Q

what are racemases and epimerases?

A

isomerase enzymes that catalyzes the inversion of stereochemistry

racemases: catalyzes sterochemical inversion around the asymmetric carbon atom (in a substrate has only one center of asymmetry)
epimerases: catalyzes sterochemical inversion of the configuration around an asymmetric carbon (in a substrate with more than one center of assymmetry)

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30
Q

what are ligases

A

catalyzes the joining together of two or more molecules

eg. fatty acyl CoA synthase

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31
Q

why is it necessary to purify enzymes

A

to remove undesirable components from source materials (ie toxins and other enzymes)

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32
Q

steps in enzyme purification

A

extration then purification

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33
Q

describe the extraction process

A
  1. blend or homogenize raw materials in buffer solution
  2. filtration
  3. results in crude enzyme extract (But may still have other enzyme components: salt, nucleic acids, sugars, enzymes, minerals)
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34
Q

what are enzyme purification methods that are based on size differences

A

dialysis
ultrafiltration
centrifugation
gel filtration

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35
Q

describe the dialysis enzyme purification process

A
  • uses a dialysis bag (semipermeable membrane with polysaccharide)
  1. sample is placed into dialysis bag
  2. bag is placed in beaker with solvent solution that is lower than conc that solution in bag
  3. small molecules in sample travel through pore to outside of dialysis bag, but larger molecules stay inside bag
  4. process continues until equilibrium concentration
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36
Q

is the dialysis process efficient?

A

no because molecules can still re-enter into bag at equilibrium concentration

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37
Q

describe the ultrafiltration process

A
  • purification based on size difference
  • uses semi permeable membrane
  • uses pressure from gas (N2) or vacuum to force small molecules through pores in membrane
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38
Q

describe the centrifugation process

A
  • purification based on size difference
  • uses centrifugal force for large molecules o go to the bottom as fast as possible
  • larger and heavier molecules sediment faster than small and light molecules
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39
Q

in centrifugation, which molecules sediment faster?

A

large/ heavier are faster than small and light

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40
Q

describe the gel filtration chromatography

A
  • purification based on size difference
    1. place resin in column
    2. apply sample on top of column
    3. sample will migrate down column

large molecules elute faster than small ones

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41
Q

in gel filtration, what size molecules pass through (or elute) faster

A

large molecules elute faster

42
Q

what are 3 methods of purification based on solubility differences

A
  1. isoelectric precipitation
  2. salt fractionation
  3. solvent precipitation
43
Q

describe isoelectric precipiation

A

at the isoelectric point, E has minimal solubility

when Pi = pH of an enzyme, the enzyme will precipitate

44
Q

describe salt fractionation

A

type of protein separation based on SOLUBILITY DIFFERENCE

  1. adding neutral salts (eg ammonium sulfate) to compress the solvation layer and increase protein-protein interactions.
  2. charges on surface of protein interacts with the salt –> exposes hydrophobic patches on protein surfaces –> causes protein to fall out of solution –> aggregation and precipitation
  3. ionic strength increases –> proteins interact via hydrophobic pathes on surface
45
Q

why is ammonium sulfate used in salt fractionation

A

since it preserves protein activity and promotes precipitation at lower concentrations than other salts

46
Q

describe what salting in and out is. (salt fractionation)

A

salting in: when protein solubility increases (at low salt concentrations)

salting out; when protein solubility decreases (at high salt concentrations)

47
Q

describe solvent precipitation

A

type of protein separation based on SOLUBILITY DIFFERENCE

  1. adding miscible solvents (eg ethanol or methanol) to cause proteins in solution to precipitate. (Miscible organic solvents decrease dielectric constant to water, which allows proteins to come close together)
  2. solvation layer around protein decreases as the organic solvent displaces water from protein surface and binds it in hydration layers around the organic solvent molecule
48
Q

what is the use of miscible organic solvents in solvent precipitation?

A

they decrease dielectric constant to water

allows two proteins to come close together

49
Q

what are protein separation methods based on charge differences

A
  1. ion exchange chromatography
  2. electrphoresis
  3. isoelectric focusing (IEF)
50
Q

what are protein separation methods based on specific binding sites

A
  1. affinity chromatography
  2. hydrophobic interaction chromatography (HIC)
  3. hydrophillic interaction chromatography (HILIC)
51
Q

describe ion exchange chromatography

A

type of protein separation based on CHARGE DIFFERENCE

  • purifying a negatively charged enzyme using IEX
    1. resin is positively charged
    2. apply sample
    3. negatively charged enzyme binds resin
    4. positively charged enzymes won’t bind and will elute using buffer
    5. bound enzymes are removed by charging the pH or ion strength of the elution buffer
52
Q

describe electrophoresis

A

type of protein separation based on CHARGE DIFFERENCE

  1. restriction enzymes cleave DNA into smaller segments of various sizes
  2. DNA segments are loaded into wells in a porous gel
  3. gel floats in buffer solution within a chamber between two electrodes
  4. an electric current is passed through the chamber –> DNA gragments move towards pos-charged cathode
  5. similar DNA segments move faster and farther than larger DNA segments
53
Q

describe isoelectric focusing (IEF)

A

type of protein separation based on CHARGE DIFFERENCE

  • uses a gel made of AA and peptides
  • pH gradient gel is generated by ampholyte
  1. apply electric current
  2. E with different charges will migrate up to a pH point in the gel until overall charge of the E is 0
  3. sample with pos charge moves toward cathode. Sample with neg charge moves towards anode
54
Q

what are anion and cation exchanges (in ion exchange chromatogrpahy)?

A

anion exchange: pos charged particles that bind with negatively charged resin

cation exchanges: neg charged particles that bind with pos charged resin

55
Q

what is SDS page

A

involved in ion exchange chromatography

mobility is related to size of enzyme

aka polyacrylamide gel electrophoresis (used to separate molecules based on electrophoretic mobility)

56
Q

what does amypholyte do in IEF?

A

generates a pH gradient gel

57
Q

describe affinity chromatography

A

enyzmes with specific binding will bind to substances in resin

unbound enzymes will elute from column first

bound enzymes can be washed out of column by changing the pH or ion strength of elution buffer

58
Q

describe hydrophobic interaction chromatography (HIC)

A
  1. Hydrophobic groups are attached to stationary column. If stationary phase is too weak in water, buffers (ie. Na2SO4 and NaCl) are added)
  2. Proteins with hydrophobic AA side chains on their surfaces interact with and bind to groups on the column
  3. Buffer with high ionic strength (eg. Ammonium sulfate) is applied to the column –> reduces solvation of sample solutes –> solvation decreases and hydrophobic regions are absorbed by the medium

(higher hydrophobicity = less salt is needed)

  1. molecules elute in order of increasing hydrophobicity
59
Q

describe hydrophillic interaction chromatography (HILIC)

A
  • separates polar and hydrophillic compounds with an amide/amino bonded phase column
  • involves polar stationary (retains polar compounds) phase and mobile phase
60
Q

in HIC, higher hydrophobicity means ___ salt is needed

A

less

61
Q

how do enzymes facilitate reactions?

A

by reducing the energy barrier

62
Q

In the transition state theory, what is the activation energy?

A

minimum energy needed to overcome the energy barrier to get to the activated complex of the transition state

delta G = (energy of transition – energy of substrate)

63
Q

what does a higher activation energy mean?

A

harder for reaction to occur

64
Q

how do enzymes lower activation energy?

A

Decreases the delta G to achieve the transition state (delta G catalyzed is much smaller than delta G un-catalyzed)

E can transiently bind with S to produce a transition state “ES” having a lower energy of activation that the transition state of un-catalyzed reaction

S + E ES –> E+P

65
Q

how can we measure enzyme activity?

A

rxn rate of enzymatic reaction

66
Q

how can we measure rxn rate?

A
  1. measure rate of disappearance of S

2. measure rate of formation of P (normally used)

67
Q

describe the state of substrates and products during at the beginning of a reaction

A
  • S is saturated
  • P production is increasing in a linear relation with t

Rx = delta [P] / delta t
(constant slope)

68
Q

describe the state of substrates and products after some time after the beginning of a reaction

A
  • S is saturated
  • P is increasing but slowing down

Rx = delta [P] / delta t
(Rx is decreasing)

69
Q

describe the state of substrates and products after a long time after the beginning of a reaction

A
  • S is finished
  • P is 0 (no production of enzyme. Amount of enzyme remains constant)
  • thus, Rx = 0 (slope becomes horizontal)
70
Q

what are the 2 types of initial rate experiment?

A
  1. continuous method: with catalysis taking place, measuring the Rx rate within the linear period
  2. discontinuous method (aka end point method): after catalysis takes place, some chemicals (ie acids, alkali, inhibitors) are added to stop the reaction
71
Q

what does the overall reaction rate depend on?

A

[E], [S], T, stability of ES, [P], pH, etc…

72
Q

if the enzyme concentration increases, catalysis ___?

A

increases

73
Q

if the substrate concentration increases, catalysis ___?

A

increases up to a certain point until the enzyme is saturated

74
Q

a lower KM means ____ affinity

A

higher

75
Q

how do you increase rxn rate? how to decrease rxn rate?

A

increase: raising temperature or pressure
decrease: catalysts (lowers activation energy)

76
Q

a high Vmax/Km ratio means…?

A

high efficiency

77
Q

what is competitive inhibition

A

when compounds compete for same active site

will decrease amount of substrates bounded and products produced

78
Q

what is non-competitive inhiibtion

A

inhibitor can bind anywhere other than active site (doesn’t affect substrates or products)

79
Q

what is uncompetitive inhibition

A

inhibitor binds to site on enzyme which becomes available only after substrate has bound to active site

80
Q

how to relieve competitive inhibitions

A

increase [s]

81
Q

how to relieve non-competitive inhibitions

A

remove inhibitors using separation techniques

82
Q

how to relieve un-competitive inhibitions

A

dilute [s] or add [E]

83
Q

describe the bell shaped graph (effect of temperature on enzyme catalysis)

A
  1. low temp slows down enzyme catalysis
  2. as temp increases, enzyme catalysis increases (Q10 rule)
  3. after optimal temp, catalysis of enzyme decreases
  4. extreme high temp denatures enzymes
84
Q

what is optimum enzyme pH

A

5-8

85
Q

optimum oH of pepsin?

A

1.5

86
Q

what enzyme has a broad optimum pH range?

A

papain (papaya proteinase)

87
Q

beneficial aspedts of enzymes in food industry

A
  1. natural and non toxic
  2. specific (uniform product)
  3. efficient
  4. enzymes can be inactivated by heat or pH
  5. enzymes can be re-used
88
Q

what is an immobilized enzyme

A

protein hydrolyzed by trypsin to get protein hydrolates

89
Q

waht are undesirable effects of enzymes

A
  1. enzymatic browning by PPO
  2. spoilage
    3, safety issues
90
Q

what are enzymes that cause flavor change in spoilage?

A
  1. lipooygenase (LOX): catalyzes oxidation of unsat FA causing odors in foods (unsat FA + O2 –> Fa hydroperoxide)
  2. lipase: causes rancid odor in FA that are not stable
  3. proteases: can form bitter peptides in protein foods
91
Q

what are undesirable effects of safety issues of histidine?

A

histidine is toxic and gives an off-odor

92
Q

disirable and undesirable effects are….?

A

relative

93
Q

what are desirable effects of PPO?

A

black tea and coffee

94
Q

desirable effects of LOX?

A

blanching flour by degrading pigments

95
Q

what is the most common source of industrial enzymes?

A

microbial sources

80-90%

grows fast and needs only limited space and nutrients

eg amylase and transglutaminase

96
Q

what is transglutaminase:

A

catalyzes cross linking of proteins to form firm texture

used in meat recombination and restructing

97
Q

use of glucose isomerase?

A

converts glucose to fructose in corn syrup

98
Q

chemical reactions in oxidoreductases?

A
  1. PPO
  2. peroxidase
  3. LOX
  4. glucose oxidase
  5. ascorbic acid oxidase
99
Q

what does glucose oxidase do? what is it?

A

it is an oxidoreductase

oxidizes glucose into gluconic acid

100
Q

describe fresh broccoli sterilization using peroxidase

A

can be used to determine if broccoli treatment involved heat

if peroxidase activity is how, it means they used high sterilization temp

Food Chemistry 2 (4 decks)

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