enzymes Flashcards
What are some examples of processes that would take a very long time in the absence of enzymes?
○ Extracting energy from glucose
○ Burning hydrocarbon fuels
○ Nitrogen fixation
○ Digesting food
What are the two ways a reaction can be accelerated?
- Adding heat: Increases the number of reactants with sufficient energy to overcome the activation energy barrier.
- Adding a catalyst: Decreases the activation energy barrier but does not react.
What are enzymes?
○ Mostly proteins.
○ Have primary, secondary, tertiary, and quaternary structures.
○ Typically globular proteins.
○ Their structure is determined by the same forces that govern protein structure (e.g., hydrogen bonds, Van der Waals interactions).
What are the key characteristics of enzymes as catalysts?
○ They accelerate reaction rates.
○ They are regenerated at the end of the reaction.
○ Can increase reaction rates by 106 to 1020 fold.
○ Highly specific for their substrates.
○ Do not produce side reactions.
What are some common features of enzyme nomenclature?
○ Enzyme names typically end in “-ase”.
○ The name often describes the process, substrate, product, or chemical reaction.
Ex: Citrate synthase, alcohol dehydrogenase, pyruvate decarboxylase.
How are enzymes regulated?
Enzymes are regulated through
* allosteric regulation
* competitive inhibiton
* reversible covalent modification
* gene expression and subcellular localization
* feedback inhibition
* Ionic signals
* substrate availability
Their structures are flexible & changing their shape can alter their function
What determines the speed of a thermodynamically favorable biochemical reaction?
the size of the activation energy barrier.
Do enzymes affect the free-energy change (ΔG) of a reaction?
No, they only affect the activation energy.
How do enzymes reduce the free energy of the transition state?
○ Removing substrates from aqueous solution (desolvation).
○ Proximity and orientation effects.
○ Taking part in the reaction mechanism.
○ Stabilizing the transition state.
What is the active site of an enzyme?
- The region of the enzyme where catalysis occurs.
- Usually a small portion of the protein.
- Contains key amino acids involved in binding and catalysis.
- Determines affinity, specificity, and rate of the reaction.
- Complementary to the substrate or transition state.
- Shape, hydrophobic interactions, hydrogen bonds, and ion pairs contribute to substrate binding.
Describe the lock and key model of enzyme-substrate binding.
This model suggests a rigid interaction where the enzyme’s active site is a perfect fit for the substrate, like a lock and key.
Describe the induced fit model of enzyme-substrate binding.
This model proposes that the active site changes shape as the substrate binds, leading to a more precise fit
What are the advantages of desolvation in enzyme catalysis?
- Removal of the water shell accelerates reactions.
- Enhances polar interactions (hydrogen bonds, ion pairs).
- Prevents side reactions
How do proximity and orientation effects contribute to catalysis?
○ Chemical reactions require substrates to come together in the correct orientation.
○ Active sites bind substrates close to each other (proximity) and in the correct geometry (orientation).
○ This can enhance reaction rates by up to a thousandfold.
How can enzymes participate in reactions?
○ Some enzymes use functional groups in the active site to participate in reactions.
○ These groups may act as:
■ Acid/base catalysts
■ Covalent catalysts
■ Metal ion catalysts
○This can be achieved through amino acids or cofactors (or both).