Enzymes and the Principles of Catalysis Flashcards
(29 cards)
Why are enzymes necessary for life
They accelerate metabolism and biochemical reactions, making them fast and specific enough to sustain life
What is an example of an enzyme that accelerates a crucial metabolic step
Hexokinase – it helps align substrates properly and excludes water from the active site to prevent side reactions with ATP
Why must glycolysis be efficient
Because ATP production alone doesn’t provide enough energy; efficient catalysis is necessary for viability
How do enzymes accelerate reactions
By stabilising the transition state, lowering the activation energy (Ea)
What is the transition state
A high-energy, unstable intermediate between substrate and product
Do enzymes affect reaction equilibrium
No they affect kinetics not the equilibrium position
What is the role of the enzyme active site in catalysis
It promotes transition state formation by being complementary to the transition state, not the substrate
What happens if the enzyme is too complementary to the substrate
ΔG becomes too high, and the substrate is less likely to convert to the transition state
What are the general features of an active site
A crevice in the enzyme
Key catalytic groups precisely oriented
Typically excludes water unless it’s a reactant
Mostly hydrophobic but includes some hydrophilic residues for catalysis
What are the two functional areas of an active site
- Binding site – binds and orients substrates
- Catalytic site – reduces activation energy, chemically reactive
What is covalent catalysis
The enzyme forms a temporary covalent bond with the substrate
What is acid-base catalysis
A molecule (other than water) donates or accepts protons during the reaction
What is metal ion catalysis
Metal ions bind substrates, stabilise negative charges, and assist oxidation reactions
What does enhancing proximity of reactants do
Increases the likelihood of functional group transfer between molecules
How does chymotrypsin catalyze reactions
Uses a nucleophile to attack the unreactive carbonyl in peptide bond hydrolysis
What are the four examples of enzymes with similar catalytic mechanisms
- Acetylcholinesterase – removes acetylcholine from synapses
- Transpeptidases – break crosslinks in bacterial cell walls
- COVID-19 MPro – uses cysteine as a nucleophile
- PETases – evolved to digest plastic
What does the Michaelis-Menten model describe
Kinetic parameters of enzyme-substrate interaction and reaction rates
What does Km represent
Affinity of the enzyme for the substrate (lower Km = higher affinity)
What does kcat represent
The number of reactions per enzyme per second once the substrate is bound
What is Vmax
Vmax is the maximum velocity of an enzyme-catalysed reaction when the enzyme is saturated with substrate. It reflects the rate when all active sites are occupied
What does (kcat/Km) indicate
Catalytic efficiency of an enzyme under diluted conditions
What are the three key assumptions of the Michaelis-Menten model
- Measuring initial reaction velocity
- Substrate is in excess
- Reaction is at steady state (formation and breakdown of ES are balanced)
What does a Michaelis Mention plot show
The relationship between substrate concentration [S] (x-axis) and reaction rate (velocity) V₀ (y-axis)
Why is understanding enzyme kinetics important
It allows prediction of metabolite concentrations under steady-state conditions in cells
