Fundamentals of food enzymes Flashcards

1
Q

what are enzymes

A

complex globular protein catalysts
-accelerate the chemical reaction rate
-exist in almost all living systems, needed for metabolism

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2
Q

activity of an enzyme depends on

A

the species/source
-different foods have a different matrix resulting in a different function

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3
Q

why is knowledge of enzyme activity important

A

shelf life
behaviour of a product

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4
Q

what is the active site of a protein

A

location or portion of enzymes consisting of a binding site at which a chemical reaction occurs

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5
Q

who proposed the lock and key theory and explain it

A

fischer 1894
substrates fits like a key to binding site on protein

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6
Q

who proposed induced fit and explain it

A

Koshland 1965
dissimilar molecules can also be a substrate for the same protein, less rigid
active site is more flexible

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7
Q

what is a cofactor

A

participate directly in reactions or serve as an activator

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8
Q

why are enzyme in food different to regular chemistry

A

enzymes are not in isolation
-they are found with the substrate

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9
Q

what is found in the food matrix

A

enzymes
enzyme inhibitors
enzyme-substrate interactions
reaction products
co-factor/coenzymes
substrate
enzyme inhibitor interactions

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10
Q

what is an enzyme inhibitor

A

compound that decreases rate of enzyme-catalysed reactions

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11
Q

what can enzyme inihibitors react with

A

enzyme
enzyme-substrate complex
both

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12
Q

two classes of inhibitors

A

reversible
irreversible

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13
Q

what is enzyme activity dependant on

A

purity
location
environmental properties
Prescence of other factors
stability of enzyme

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14
Q

what effects enzyme specificity

A

bond
group
absolute specificity

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15
Q

name three types of inhibitors

A

competitive
uncompetitive
non-competitive

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16
Q

what are competitive inhibitors

A

react with the enzyme

17
Q

what are uncompetitive inhibitors

A

react with enzyme-substrate complex

18
Q

what are non-competitive inhibitors

A

react with both the enzyme and ES complex

19
Q

what influences enzyme activity

A

intrinsic: pH, substrate, cofactors, inhibitors, activators, buffer concentrations, ionic strength, water activity
extrinsic: temp, pressure, time exposure

20
Q

what is enzyme stability dependant on

A

sources
varieties
purification steps

21
Q

denaturation vs inactivation

A

denaturation: protein structure alteration
inactivation: loss of enzyme activity not necessarily due to denaturation

22
Q

temp range for most enzymes

23
Q

when do most enzyme begin to denature

24
Q

how can ice inactivate

A

ice changes structure
-may still be active before freezing so need to think how fast a thick product might freeze

25
factors that affect enzyme behaviours in partially frozen systems
composition of medium freezing rate viscosity sample complexity phase changes
26
how does viscosity in frozen systems impact enzyme activity
viscosity is high, diffusion rate is decreased
27
enzymes that can be damaged by cold denaturation
catalase lactate dehydrogenase
28
effect of pH on enzymes
extreme pH may = denaturation velocity of reaction affinity of substrate to enzyme stability of enzyme
29
optimal pH of most enzymes
4.5-8
30
optimal pH of pepsin
1.8
31
optimal pH of arginase
10
32
effect of water activity
water serves as a medium for reaction and vehicle for substrate -still active at dry conditions but rate of reaction is limited by rate of diffusion
33
effect of ionic strength
changes solubility of protein -salting in/out, protein participation
34
what is the michaelis-menten reaction used for
time course of enzyme-catalysed reactions
35
y axis of MM reaction graph
intial velocity
36
x axis of MM reaction graph
substrate concentration
37
when can maximum velocity be acheived
when there is a saturated substrate solution
38
what happens to the velocity during the reaction and why
it decreases as substrate is depleted
39