Metabolic Pathways

Overview of Metabolism

Metabolism is the sum of all chemical activities occurring inside a living cell. These activities are organized into metabolic pathways, which are series of chemical reactions that proceed in an orderly, step-by-step manner. Metabolic pathways allow one pathway to capture and use energy released in increments, making energy management more efficient for the cell.

• Reactants in enzymatic reactions are called substrates.

• The product of one reaction becomes the substrate for the next reaction in the pathway.

Enzymes

Nature and Function of Enzymes

Enzymes are usually protein molecules that act as organic catalysts to speed up chemical reactions. Every reaction in a cell requires a specific enzyme. Enzyme names are often formed by adding the suffix -ase to the name of its substrate or the reaction they perform.

• Lipase – catalyzes the hydrolysis of lipids.

• Sucrase – catalyzes the hydrolysis of sucrose.

Enzymes lower the activation energy needed for a reaction to occur, allowing reactions to proceed at cellular temperatures without the need for excessive heat.

Enzyme-Substrate Complex

Formation and Function

An enzyme-substrate complex is formed when an enzyme binds to its substrate at a specific region called the active site. The substrate attaches to the enzyme at this site, and the enzyme is not permanently altered by the reaction. Therefore, only a small amount of enzyme is needed since it can be used repeatedly.

Induced Fit Model

Mechanism of Enzyme Action

The induced fit model of an enzyme allows an enzyme-substrate complex to form by slightly altering the shape of the enzyme to achieve the best fit with the substrate. This explains the specificity of enzyme action and is similar to a key fitting into a lock, but with the enzyme undergoing a slight change in shape for optimal binding.

The Product

Outcomes of Enzymatic Reactions

• The product is the substance found at the end of a reaction.

• An enzymatic reaction can bring about synthesis (formation) or catabolism (decomposition) of a substance.

• The product of the reaction is determined by which enzyme/substrate is used.

• Enzymes cannot change the possible outcomes of a reaction; they only speed up the process.

What Affects Enzyme Productivity?

Factors Influencing Enzyme Activity

• Adding more of the substrate increases enzyme activity.

• Achieving optimum temperature and optimum pH is crucial for maximum enzyme activity.

• Inhibition can decrease enzyme productivity by blocking the active site or altering enzyme structure.

Adding More of the Substrate

Substrate Concentration and Enzyme Activity

• Enzyme activity increases as substrate concentration increases.

• There will be more collisions between the substrate and the enzyme.

• This will result in all the active sites being filled.

• Having all the active sites filled will, in turn, result in the formation of more product.

Summary Table: Enzyme Function and Regulation

Key Equations

• Activation Energy (Ea):

is the minimum energy required for a chemical reaction to proceed.

• General Enzyme Reaction:

Where E = enzyme, S = substrate, ES = enzyme-substrate complex, P = product.