Fundamentals of food enzymes

Question 1

what are enzymes

Answer 1

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

Question 2

activity of an enzyme depends on

Answer 2

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

Question 3

why is knowledge of enzyme activity important

Answer 3

shelf life
behaviour of a product

Question 4

what is the active site of a protein

Answer 4

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

Question 5

who proposed the lock and key theory and explain it

Answer 5

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

Question 6

who proposed induced fit and explain it

Answer 6

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

Question 7

what is a cofactor

Answer 7

participate directly in reactions or serve as an activator

Question 8

why are enzyme in food different to regular chemistry

Answer 8

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

Question 9

what is found in the food matrix

Answer 9

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

Question 10

what is an enzyme inhibitor

Answer 10

compound that decreases rate of enzyme-catalysed reactions

Question 11

what can enzyme inihibitors react with

Answer 11

enzyme
enzyme-substrate complex
both

Question 12

two classes of inhibitors

Answer 12

reversible
irreversible

Question 13

what is enzyme activity dependant on

Answer 13

purity
location
environmental properties
Prescence of other factors
stability of enzyme

Question 14

what effects enzyme specificity

Answer 14

bond
group
absolute specificity

Question 15

name three types of inhibitors

Answer 15

competitive
uncompetitive
non-competitive

Question 16

what are competitive inhibitors

Answer 16

react with the enzyme

Question 17

what are uncompetitive inhibitors

Answer 17

react with enzyme-substrate complex

Question 18

what are non-competitive inhibitors

Answer 18

react with both the enzyme and ES complex

Question 19

what influences enzyme activity

Answer 19

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

Question 20

what is enzyme stability dependant on

Answer 20

sources
varieties
purification steps

Question 21

denaturation vs inactivation

Answer 21

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

Question 22

temp range for most enzymes

Answer 22

30-40C

Question 23

when do most enzyme begin to denature

Answer 23

45C

Question 24

how can ice inactivate

Answer 24

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

Question 25

factors that affect enzyme behaviours in partially frozen systems

Answer 25

composition of medium
freezing rate
viscosity
sample complexity
phase changes

Question 26

how does viscosity in frozen systems impact enzyme activity

Answer 26

viscosity is high, diffusion rate is decreased

Question 27

enzymes that can be damaged by cold denaturation

Answer 27

catalase
lactate dehydrogenase

Question 28

effect of pH on enzymes

Answer 28

extreme pH may = denaturation
velocity of reaction
affinity of substrate to enzyme
stability of enzyme

Question 29

optimal pH of most enzymes

Answer 29

4.5-8

Question 30

optimal pH of pepsin

Answer 30

1.8

Question 31

optimal pH of arginase

Answer 31

10

Question 32

effect of water activity

Answer 32

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

Question 33

effect of ionic strength

Answer 33

changes solubility of protein
-salting in/out, protein participation

Question 34

what is the michaelis-menten reaction used for

Answer 34

time course of enzyme-catalysed reactions

Question 35

y axis of MM reaction graph

Answer 35

intial velocity

Question 36

x axis of MM reaction graph

Answer 36

substrate concentration

Question 37

when can maximum velocity be acheived

Answer 37

when there is a saturated substrate solution

Question 38

what happens to the velocity during the reaction and why

Answer 38

it decreases as substrate is depleted