Topic 10: Introduction to Enzymes

Question 1

What 4 factors impact rates of reactions

Answer 1

Concentration
Temperature
Enzyme activity
Surface area of solid catalyst is applicable

Question 2

How do enzymes affect the equilibrium

Answer 2

An enzyme does not change the free energy of reactants or products, and therefore does not effect the equilibrium constant, and hence does not effect the concentration of products and reactants. It simply allows the reactants to reach equilibrium quicker

Question 3

Describe the two models of enzyme-substrate activity

Answer 3

Lock-and-key model: In the lock-and-key model, enzymes are described as having a specific, rigid, and pre-existing active site that exactly matches the shape and chemical properties of their substrate.
The substrate (reactant molecule) is considered the “key” that fits perfectly into the enzyme’s “lock,” the active site. This model implies that the active site of the enzyme and the substrate have a fixed and complementary shape, and they fit together like a lock and key
The lock-and-key model suggests that the binding of the substrate to the enzyme is highly specific, and only substrates with the exact shape and properties can bind and be catalyzed.
This model doesn’t account for any conformational changes in either the enzyme or the substrate upon binding.

Induced fit model: The induced fit model, proposed by Daniel Koshland in 1958, suggests that both the enzyme and the substrate are flexible and dynamic structures. In this model, the enzyme’s active site is not a rigid, pre-existing structure but rather a flexible site that can adjust its shape upon substrate binding
The substrate is also considered to be somewhat flexible, and its binding to the enzyme induces conformational changes in both the enzyme and the substrate.
The conformational changes that occur upon binding help to optimize the fit between the enzyme and the substrate, allowing for tighter and more specific binding
The induced fit model accounts for the idea that the active site’s shape can change slightly to accommodate the substrate, and the binding is not solely dependent on a precise pre-existing match

Question 4

Define cofactors and coenzymes

Answer 4

Cofactor: A component that works with the enzyme in effecting catalysis. Any chemical factors that assist the activity of an enzyme-catalyzed reaction.

Enzymes can be divided into two categories based on their need for cofactors

Apoenzymes: These are enzyme proteins that are inactive or have reduced activity without the presence of a cofactor. Apoenzymes require the binding of a cofactor to become fully functional.
Holoenzymes: A holoenzyme is the complete, active form of an enzyme, which consists of the apoenzyme and the cofactor.
Cofactors can be further classified into two main types:

Inorganic Cofactors: These are typically metal ions that bind to the enzyme and participate in catalytic reactions. Common inorganic cofactors include ions like zinc (Zn²⁺), magnesium (Mg²⁺), iron (Fe²⁺ or Fe³⁺), and copper (Cu²⁺).
Organic Cofactors (Coenzymes): These are small, organic molecules that are required for enzyme function. Coenzymes often act as carriers of chemical groups or electrons, shuttling them between different reactions. Examples of coenzymes include NAD+ (nicotinamide adenine dinucleotide), FAD (flavin adenine dinucleotide), and coenzyme A (CoA).
Generally derive from β-vitamins