how enzymes work

Enzymes are crucial proteins that catalyze chemical reactions, performing thousands of reactions every second in living cells.
They initiate reactions, accelerate their progress, and ensure a consistent outcome regardless of the conditions.
Enzymes often operate in concert to form complex pathways, such as the citric acid cycle, which is vital for energy production in cells from carbohydrates.

Enzymes regulate critical life processes, including:
- Metabolism
- Protein synthesis
- Cell renewal and growth
They can catalyze reactions under mild conditions of pH, temperature, and pressure, which is essential for maintaining cellular environments.
The reaction rates of enzymatic reactions are dramatically faster—ranging from millions to trillions of times quicker than similar reactions occurring without enzymes.

Enzymes lower the activation energy required for reactions, allowing them to proceed more easily:
- Without an enzyme, reactions require additional energy, typically in the form of heat, to reach an unstable transition state that can lead to product formation.
Enzymes serve as templates for reactions, binding substrates in precise orientations to facilitate the formation of products.
By surrounding substrates with chemically reactive groups, enzymes stabilize the transition state, thereby accelerating the reaction.

Aconitase is an enzyme within the citric acid cycle that catalyzes a specific reaction:
- It binds to citrate and catalyzes the removal and repositioning of a hydroxyl group and hydrogen atom, transforming citrate into isocitrate through the intermediate cis aconitate.
- The process involves dehydration followed by hydration, with histidine acting as an acid and serine functioning as a base during the reaction steps.

The active site of aconitase contains strategically positioned amino acids to effectively recognize and bind substrates:
- Histidine one zero one donates protons, while serine six forty two accepts protons, facilitating the reaction.
An iron-sulfur cluster in the active site aids in stabilizing substrates and aligning them for catalysis.
The reaction proceeds through several steps that include:
1. Dehydration (removal of water) facilitated by histidine.
2. Formation of cis aconitate, which undergoes inversion.
3. Rehydration (addition of water) leading to isocitrate.
Throughout this process, the enzyme remains unchanged, highlighting its role as a catalyst:
- It reforms its original state by extracting then resupplying the hydroxyl and hydrogen groups, allowing continuous catalytic activity.

The shape of an enzyme's active site is often flexible, which helps to better enclose and interact with substrates, creating an optimal environment for reactions.
Enzymes are indispensable for life, involved constantly in maintaining cellular processes across all living organisms, underscoring their fundamental role on Earth.

Lock and Key Model: This model suggests that the enzyme's active site (the "lock") is complementary in shape to the specific substrate (the "key"). This specificity ensures that only the right substrate can fit into the active site, facilitating a reaction.
Induced Fit Model: According to this model, the active site of the enzyme is flexible and can change shape to better accommodate the substrate when it binds. This conformational change enhances the enzyme's ability to catalyze the reaction.

Enzyme activity generally increases with temperature up to an optimum point, beyond which it decreases due to denaturation (loss of structure) of the enzyme. The optimum temperature varies for different enzymes but is typically around 37°C for many human enzymes.

Inhibitor: A molecule that decreases an enzyme’s activity, thus reducing the rate of the reaction catalyzed by that enzyme.

Competitive Inhibition: The inhibitor resembles the substrate and competes for the active site of the enzyme. Its presence can be overcome by increasing substrate concentration.
Non-Competitive Inhibition: The inhibitor binds to an enzyme at a site other than the active site, altering the enzyme's shape and reducing its activity, regardless of substrate concentration.

A cofactor is a non-protein molecule that binds to the enzyme and is essential for its activity. Cofactors can be inorganic (like metal ions) or organic (like coenzymes) and assist enzymes by stabilizing transition states or participating in the chemical reaction.