Ch 6 Enzymes Flashcards
What significant discovery did NASA announce on Jan. 29, 2025?
NASA discovered amino acids on asteroid Bennu
What are the ways to increase the rate of chemical reactions?
- Increasing the temperature
- Increasing the concentrations of the reacting substances
- Adding a catalyst
What is a catalyst?
A substance that participates in the reaction yet returns to its original form
What are enzymes?
Catalysts used by living systems to increase the rates of chemical reactions
What is the active site of an enzyme?
A specific fraction of the structure where reactions take place
Most enzymes work under what conditions?
Mild conditions
True or False: Enzymes can operate under extreme temperatures and pressures.
False
What is activation energy (ΔG‡)?
Energy input needed to start the reaction
How do enzymes affect activation energy?
Enzymes lower the activation energy
What does a negative ΔG° indicate?
The reaction is spontaneous
What are the seven major classifications of enzymes?
- Oxidoreductases
- Transferases
- Hydrolases
- Lyases
- Isomerases
- Ligases
- Translocases
What is the difference between kinetics and thermodynamics?
Kinetics refers to the speed of a reaction, while thermodynamics refers to the direction and likelihood of a reaction
What is stereospecificity in enzymes?
Most enzymes are very specific with respect to the stereochemistry of substrates
What is the lock-and-key model?
A model where the substrate binds to a portion of the enzyme with a complementary shape
What is the induced fit model?
Binding of the substrate induces a change in the conformation of the enzyme for a complementary fit
What are cofactors?
Substances that aid in catalysis, including metal ions and organic molecules
What are coenzymes?
Organic molecules that act as cofactors, often derived from vitamins
What is acid-base catalysis?
A mechanism where a proton is transferred between the enzyme and the substrate
What is covalent catalysis?
A mechanism where a covalent bond forms between the catalyst and the substrate during the transition state
What is metal ion catalysis?
A mechanism where metal ions mediate oxidation-reduction reactions or promote reactivity
What is the catalytic triad?
The hydrogen-bonded arrangement of Asp, His, and Ser residues in enzymes like chymotrypsin
In the context of enzyme kinetics, what does [S] represent?
Substrate concentration
What analogy is used to describe enzyme activity and velocity?
A monkey is like an enzyme and a peanut is like a substrate
Fill in the blank: Enzymes often use _______ to aid in catalysis.
cofactors
What is enzyme kinetics?
How fast an enzyme catalyzes a reaction under a given set of conditions.
How are rates of enzyme reactions measured?
In units of product produced or substrate consumed per time period, e.g., moles/unit time.
What does Chymotrypsin catalyze?
The selective hydrolysis of peptide bonds, particularly at Phe and Tyr residues.
What is the significance of color change in measuring chymotrypsin activity?
It indicates the rate of colored product formation.
What is Vmax?
The maximum processing speed of the enzyme when it is saturated with substrate.
Is Vmax a constant value?
No, it is dependent on the amount and type of enzyme.
What describes the relationship between initial rate of an enzyme-catalyzed reaction and substrate concentration?
Many enzymes obey Michaelis–Menten kinetics.
What characterizes a unimolecular reaction?
It has a velocity dependent on the concentration of only one substrate.
What is the rate equation for a unimolecular reaction?
𝜈 = k [A], where k has units of sec–1.
What characterizes a bimolecular reaction?
It has a velocity dependent on two substrate concentrations.
What is the rate equation for a bimolecular reaction?
𝜈 = k [A] [B] or k [A]² or k [B]², where k has units of M–1 ⋅ sec–1.
What does ‘steady state’ mean in enzyme kinetics?
It refers to a constant value of the enzyme-substrate complex (E∙S).
Who developed enzyme kinetics?
Maud Menten, MD/PhD, around 1913 in Berlin.
What does KM represent in enzyme kinetics?
The concentration of substrate at which half of the enzyme’s active sites are bound to substrate (½ Vmax).
What does a high KM value indicate?
A low substrate affinity.
What does a low KM value indicate?
A high substrate affinity.
Fill in the blank: The maximum rate when the enzyme is saturated with substrate is called _______.
Vmax
If two enzymes have the same Vmax, how is the enzyme with a higher affinity for substrate determined?
The enzyme with the lower KM value has the higher affinity.
