Ppt 2 Flashcards
Reacting molecules in enzyme catalysis (conversion of R to P) must overcome what?
Energy barrier
How do enzymes facilitate reactions?
reduce the energy barrier
What is a catalyst?
an agent that accelerates the rate of reaction without undergoing net chemical modification. Reduces energy barrier required to transform a reactant to product
What is the simplest way to quantitatively account for rates of chemical reactions/catalysy?
Collision theory
What is the formula for the collision theory? What does each variable stand for?
K=PXe^(-Ea/RT)
- K = reaction constant
- P = probability of reaction
- Z = collision frequency
- Ea = activation energy
- R = gas constant
- T = temperature
What is the transition state theory?
For a reaction of [S] to (P) to occur, the ground state S must reach “activated or transition” state - becomes committed to forming P
Activation energy is the difference between what?
energy of S and transition state
What is delta G?
The minimum amount of energy needed to overcome the energy barrier to get to the activated complex of the transition state
The ______ the activation energy, the more difficult it is for the reaction to occur
larger
Enzymes as a type of ______ accelerate the chemical reactions by ______ the activation energy
- catalyst
2. lowering
What is the equation for an enzymatic reaction?
E + S –>(arrow goes both ways)–> ES –> E + P
How can we measure reaction rate?
rate of disappearance of S or rate of formation of P
How do enzymes enhance reactions?
Bind with S to form complex with a lower delta G
What does the overall Rx rate depend on?
[E], [S], T, stability of ES, [P], pH
In what 2 ways can reaction rate be measured?
- appearance of P
2. disappearance of S
What are 2 methods used in initial rate experiments?
- continuous method
2. discontinuous method
Continuous method
while the catalysis is taking place measure/calculate the reaction rate within the linear period
discontinuous method
stop the reaction or create an end point (also called end pt method). After catalysis has been taking place for some time, some chemicals such as acids, alkali, inhibitors are added to stop the reaction.
Rx =
(delta [P])/(delta t)
3 advantages of continuous method
- easy to find linear range
- enzyme is active
- finish in short time
2 disadvantages of continuous method
- expensive equipment
2. need good experimental skills
2 advantages of discontinuous method
- cheap equipment
2. easy to preform
3 disadvantages of discontinuous method
- may be beyond linear range
- enzyme is denatured or inhibited
- time consuming
What are 8 different factors that influence enzyme catalysis?
- [E]
- [S]
- Temp
- pH
- activation
- ions or ion strength
- inhibitors
- solvent
Km’ =
affinity of E for S
Vmax =
ease of catalysis
Vmax/Km =
catalytic efficiency
What do inhibitors cause?
reduction rates in enzyme-catalysis
Is inhibition reversible, irreversible, or both?
both
What 3 type of inhibitions are reversible?
competitive, non-competitive, uncompetitive
What must be done to relieve competitive inhibition?
dilute [S] or add [E]
What must be done to release the inhibitors in non-competitive inhibition?
remove inhibitors via separation techniques
Example uncompetitive inhibition?
high sucrose concentration in the reaction {sucrose –>glucose + fructose} invertase enzyme and water allow reaction to proceed. Addition of more sucrose inhibits invertase.
What industry uses uncompetitive inhibition?
confection industry to produce fructose (not easy to crystallize)
What are 2 examples of competitive inhibition?
- natural compounds inhibit lipase
2. glycosidase - control obesity, diabetes
Irreversible inhibition. Ex?
covalently binds with E & inactivates it. Common separation techniques can not receive the irreversible inhibitors
High [acid], [alkali], [metals], [salts]
Competitive
inhibition
1 example
I binds to active site of E, prevents S from binding. I resembles S in structure.
inhibition of succinate dehydrogenase by malonate
Uncompetitive
inhibition
1 example
I binds to site on E molecule which becomes available only after S has bound to the active site and formed ES complex.
S inhibition which occurs at very high [S]. Inhibition of invertase by high [sucrose]
Effect of low temperature on enzyme catalysis. Why is it used for food
Slows enzyme catalysis. Used in food to retard undesirable effects like texture softening, off flavours, ripening
Effect of high temperature on enzyme catalysis
enhances enzyme catalysis but may deactivate enzymes
What does the peak of a Velocity vs Temp graph represent?
Temperature optimum
Q10 rule + formula
rate of enzymatic reaction increases x2 with every 10 degree change
Q10 = (Reaction Rate at T+10C)/(rate at T) = 2
What are 2 examples of food processes that expose enzymes to high temperatures and may denature them?
- blanching
2. pasteurization
What are 7 factors that are affected by temperature during enzyme catalysis?
- enzyme stability
- affinity of E for S, I or Activators
- rate of conversion of S to P
- Changes in solubility of gases
- pH of buffer
- competing reactions
- ionization of prototypic groups
A graph of Enzyme Activity vs. Tempurature takes what shape? Where is activation and inactivation represented on this graph?
Bell-shaped
Activation < optimum temp
Inactivation > optimum temp
What are the 2 equations of Arrhenius Equation?
Draw graph
k = Ae^(Ea/RT)
Ln (x) K = LnA - Ea/RT
Under what pH range are enzymes normally optimum?
5-8
What is pepsin’s optimum pH?
1.5
What enzyme has a broad pH range? What is it?
Papain: 4-8
What are endogenous enzymes?
food enzymes that exist in food, affect the quality
What are exegenous enzymes?
added to food to cause DESIRABLE change
What are 5 beneficial aspect of pH and temp on enzyme catalysis?
- natural/non-toxic
- specificity - uniform products
- efficient - small amount under mild reaction conditions
- enzyme can be inactivated after desirable catalysis achieved
- enzyme can be recovered/reused
Steps to immobilize trypsin
Draw this out
- trypsin used to hydrolyze protein into peptides
- add hydrolase
- blanching / high temp - now you have killed trypsin and hydrolase
- use materials like resin to immobilize E in solution
- centrifuge to take out trypsin that is on the resin
- now left with only hydrolase in solution
