Exam 2 (6) - Enzymes Flashcards
What is a Catalyst?
Speed up chemical reactions but are unchanged by the reaction
What is an enzyme?
Large Protein —> Catalysts
What are substrates?
Reactant of enzymatically accelerated reaction.
Each enzyme accelerates specific reactions. (T/F)
True
Each enzyme in metabolic pathway requires a unique and specific enzyme ( T/F)
True
What is necessary for the end product to appear in a metabolic pathway?
All enzymes need to be present and functional. ( precisely regulated)
What is the energy of activation?
- reactants are often reluctant to participate in reactions
- energy must be added to 1 or more reactants
- enzymes operate by LOWERING the energy of activation
How do enzymes lower the energy of activation?
1) bring substrates into contact w/ one another
2) strain/ stretch the bonds in reactants
3) changing the local environment of reactant
4) Adding or removing functional group to or from substrate
What is the cleft/grove on the surface of the large enzyme?
active site
What does the substrate bind to?
The active site
What is the induced fit model?
shape change forces substrates together insinuating bond
What happens when a specific substrate binds to an active site?
It causes the active site to change shape
- induced fit model
The same enzyme can catalyze the forward reaction and the reverse reaction. T/F
T, both a degradation reaction and a synthesis reaction are possible with the same enzyme
General sequence for an enzymatically catalyzed sequence
?
E+Substrate–> E-S complex–> E + Products
How would a degradation reaction work with the general sequence for enzyme reactions?
- Enzyme complexes with a single substrate molecule
- Substrate Is broken apart into two product molecules ( Hydrolysis)
- Enzyme walks away unharmed
How would a synthesis reaction work with the general sequence for enzyme reactions?
- Enzyme complexes with two substrate molecules
- Substrates are joined together and released as a single product molecule
What are the factors that affect enzyme reactions?
- Enzyme concentration
- Substrate concentration
-Vmax
-temperature - pH
- denaturation,
-cofactors - coenzymes (vitamins)
- modulators or inhibitors
How does Enzyme concentration affect the rate of a reaction?
The rxn rate increases as enzyme conc increases ( w/excess substrate) — a linear relationship
How does substrate concentration affect the rate of a reaction?
- enzyme activity increases w/ substrate concentration to a point ( saturation)
- more collisions between substrate molecules and the enzyme
- Vmax
What is Vmax?
plateau where nearly all active sites are occupied by substrates
What is the relationship between Km and affinity?
Lower Km =Higher affinity
What is Km
1/2 Vmax
What is the relationship between enzymes and temperature?
temp. increase = enzyme activity increase
( too high for too long = denaturation)
What is the relationship between enzymes and pH?
most enzymes are optimized for a particular ph
What are cofactors
inorganic molecules required to activate enzymes
What are coenzymes
organic molecules required to activate enzymes
what is a modulator?
enhances enzyme activity
what is an inhibitor?
blocks enzyme activity
What are the different kinds of enzyme inhibitors?
- competitive inhibition
-noncompetitive inhibition
-feedback inhibition - irreversible inhibition
What is competitive inhibition?
Substrate and inhibitor are both able to bind to the active site
- normally inhibitors can bind more tightly, and high affinity
- inhibitor temporarily binds to active site blocking normal molecule
What is noncompetitive inhibition?
the inhibitor binds not at the active site, but at the allosteric site
what is the allosteric site?
Some other pocket or groove on that enzyme that binds with the inhibitor or modulator
why is feedback inhibition important?
- can be both competitive or non-competitive
- found in all cells
- an important regulatory process in enzyme function.
-
what is feedback inhibition?
Where some end product feeds back into an early step and shuts the enzyme off temporarily ( until it is needed again)
What is irreversible inhibition?
Materials that irreversibly inhibit an enzyme.
poison
Materials that irreversibly inhibit an enzyme.
PRACTICE QUESTION:
An alcoholic can be treated with Antabuse. This drug causes the accumulation of acetaldehyde, an alcohol byproduct, resulting in chest pains, headaches, vomiting, anxiety, and other symptoms, causing the patient to cease alcohol consumption. Acetaldehyde is normally degraded by the enzyme aldehyde oxidase. The Antabuse molecule resembles acetaldehyde. Use YOUR knowledge of enzymes to speculate as to how the drug may work.
This is a case of competitive inhibition. Antabuse replaces acetaldehyde at the enzyme’s active site preventing the enzyme from degrading its normal substrate. The buildup of acetaldehyde leads to unpleasant symptoms the more the person drinks alcohol.
