30 Questions
What happens to the rate of an enzyme-catalyzed reaction when the substrate concentration becomes the limiting factor?
It becomes independent of the enzyme concentration
What is the relationship between enzyme concentration and reaction rate when substrate concentration is not limiting?
Directly proportional
What is the significance of the Q10 value in enzyme-controlled reactions?
Quantifies the rate increase with temperature rise
Why do cold-water fish die at 30°C?
Their enzymes denature at this temperature
What happens to most enzymes at 70°C?
They denature completely
What is the pH range preferred by most enzymes for optimal activity?
Neutral (pH 6-8)
What induces a change in the enzyme's conformation when it combines with a substrate?
Stretching of substrate bonds
What is the primary function of the active site of an enzyme?
To make the chemical environment suitable for the reaction
In the Michaelis-Menten equation, what does the KS constant stand for?
Enzyme-substrate complex concentration
According to Michaelis and Menten's assumptions, what is a key aspect of the enzymatic reaction?
Low substrate concentration compared to enzymes
What is the primary focus of the Michaelis-Menten equation?
Velocity of enzymatic reactions with a single substrate
What is one assumption made by Michaelis and Menten about enzyme reactions?
The process continues essentially to its completion
What is the Michaelis-Menten constant denoted by in the given equation?
Km
How is enzyme activity commonly expressed?
Moles of substrate converted to product per unit time
Why does the rate of an enzyme-catalyzed reaction increase with an increase in substrate concentration?
More substrate molecules collide with enzyme molecules
In what scenario would the initial rate of an enzyme-catalyzed reaction be proportional to the concentration of enzyme ([E])?
[S] > [E]
How does an increase in enzyme concentration affect the reaction rate?
Increases reaction rate
At what point does an enzyme become saturated in terms of substrate concentration?
When further increase in substrate has no effect on reaction rate
What is the primary role of inorganic metal ions in enzyme catalysis?
Forming coordination bonds with side chains at the active site
Which coenzyme is responsible for transferring acyl groups during metabolic reactions?
Coenzyme A
What is the function of a transient carrier coenzyme in biochemical reactions?
Transferring specific atoms or functional groups
Which vitamin serves as a dietary precursor for mammals and is essential for various carboxylation reactions?
Biotin
What is the main function of inhibitors on enzyme activities?
To lower the enzyme's catalytic rate
Which inorganic element acts as a cofactor for the enzyme carbonic anhydrase?
Zn2+
What is a coenzyme when it comes to enzyme cofactors?
An organic compound
Which type of cofactor is referred to as a prosthetic group?
Organic or inorganic compounds tightly bound to the apoenzyme
What is the composition of a holoenzyme?
Apoenzyme + Coenzyme
In enzyme catalysis, coenzymes often function as what?
Intermediate carriers of electrons
What role does NAD play in certain oxidations/reductions?
Carrier of electrons
What distinguishes coenzymes from other enzyme cofactors?
Their association with the enzyme is transient
Study Notes
Enzyme Catalysed Reactions
- The rate of an enzyme-catalysed reaction is directly proportional to the enzyme concentration when the substrate concentration is not limiting.
- Increasing enzyme concentration will increase the rate of reaction until the substrate concentration becomes the limiting factor.
Effect of Temperature on Velocity
- Enzymes have an optimal temperature, with a balance between the Q10 (temperature coefficient) and denaturation.
- Q10 is the increase in reaction rate with a 10°C rise in temperature, with a typical value of 2-3 for chemical reactions.
- Most enzymes are fully denatured at 70°C, but some can withstand high temperatures up to 100°C.
Effect of pH Value on Velocity
- The pH optimum varies for different enzymes, with most having a neutral pH (6-8).
- When a substrate combines with an enzyme, it induces a change in the enzyme's conformation, making the chemical environment suitable for the reaction.
Michaelis-Menten Equation
- The Michaelis-Menten equation describes the velocity of enzymatic reactions, with the equation: VO = Vmax[S] / Km + [S]
- VO is the initial velocity of the reaction, Vmax is the maximum velocity, Km is the Michaelis-Menten constant, and [S] is the substrate concentration.
Enzyme Velocity and Activity
- Enzyme activity is expressed by the initial rate (V0) of the reaction being catalyzed.
- Enzyme activity is measured in moles of substrate converted to product per unit time.
- Velocity decreases as time increases due to factors such as substrate depletion, product inhibition, pH change, and cofactor depletion.
Effect of Substrate Concentration
- An increase in substrate concentration increases the rate of enzyme-catalysed reaction, but eventually reaches a point of saturation where further increases have no effect.
Effect of Enzyme Concentration
- The initial rate of an enzyme-catalysed reaction is proportionate to the concentration of enzyme.
Coenzymes and Cofactors
- Coenzymes are organic molecules that are derivatives of vitamins and act as transient carriers of specific atoms or functional groups.
- Examples of coenzymes include Coenzyme A, Flavin adenine dinucleotide, and Nicotinamide adenine dinucleotide.
- Inorganic metal ions such as Cu2+, Fe2+/Fe3+, K+, Mg2+, Mn2+, Mo, Ni2+, Se, and Zn2+ serve as cofactors by forming coordination bonds with side chains at the active site and with the substrate.
Inhibition of Enzyme Activities
- Inhibitors are molecules that act directly on an enzyme to lower its catalytic rate, often at low concentrations and with specificity.
- Cofactors can be organic compounds (coenzymes) or inorganic groups (metal ions).
- Prosthetic groups are organic or inorganic compounds that are tightly bound to the apoenzyme.
Learn about how substrates combine with enzymes to induce a change in conformation, create a suitable chemical environment for reactions, and lower the activation energy. Explore the Michaelis-Menten equation and different mechanisms of enzyme reactions proposed by biochemists.
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