C1.1.1 Enzymes as catalysts Notes

Enzymes as Catalysts

1. Enzymes are biological catalysts that increase the rate of chemical reactions without being consumed in the process.
2. They achieve this by lowering the activation energy required for a reaction to occur.

How Enzymes Work

1. Enzymes are globular proteins with a specific region called the active site, where the substrate binds.
2. The interaction between the enzyme and substrate follows the induced-fit model:
   1. Substrate Approaches: The substrate moves close to the enzyme’s active site.
   2. Binding: The active site undergoes a slight conformational change to fit the substrate more snugly.
   3. Catalysis: The enzyme lowers the activation energy, facilitating the conversion of the substrate into products.
   4. Release: The products are released, and the enzyme returns to its original shape, ready to catalyse another reaction.

Why Enzymes Are Essential in Cells

1. Speeding Up Metabolic Reactions

1. Metabolism consists of thousands of interconnected chemical reactions, divided into two main types:
   1. Anabolic reactions: Build larger molecules from smaller ones (e.g., protein synthesis).
   2. Catabolic reactions: Break down larger molecules into smaller ones (e.g., digestion).
2. Without enzymes, these reactions would occur too slowly to sustain life.

2. Lowering Activation Energy

1. Enzymes reduce the energy barrier required for reactions to proceed.
2. This allows reactions to occur at the moderate temperatures and pressures found in living organisms.

3. Specificity and Control

1. Enzymes are highly specific, meaning each enzyme catalyses only one type of reaction or acts on a specific substrate.
2. This specificity allows cells to control their metabolic pathways precisely.

Intracellular and Extracellular Enzymes

1. Enzymes can function both inside and outside cells:
   1. Intracellular enzymes: Operate within cells to catalyse metabolic reactions (e.g., enzymes in glycolysis).
   2. Extracellular enzymes: Are secreted to work outside cells, such as in digestion (e.g., amylase breaking down starch in the mouth).

Measuring Enzyme Activity

1. Enzyme activity is often measured by the rate at which substrates are converted into products.
2. Several factors can influence this rate:
   1. Temperature: Higher temperatures increase molecular motion, leading to more frequent collisions between enzymes and substrates. However, extreme heat can denature enzymes, reducing their activity.
   2. pH: Each enzyme has an optimal pH range. Deviations from this range can alter the enzyme’s structure and reduce its activity.
   3. Substrate concentration: Increasing substrate concentration initially increases the reaction rate, but the rate plateaus when all active sites are occupied (saturation point).

Why Enzyme-Catalysed Reactions Matter

1. Enzyme-catalysed reactions are fundamental to life.
2. Without enzymes, most biochemical reactions in living organisms would be too slow to sustain life.
3. Enzymes ensure specificity, meaning they only catalyze certain reactions, reducing the likelihood of harmful side reactions.
4. Enzyme activity is essential for maintaining homeostasis and supporting processes like digestion, metabolism, and cellular repair. They enable processes like:
   1. Respiration: Enzymes in the mitochondria facilitate the breakdown of glucose to produce ATP, the energy currency of cells.
   2. Digestion: Enzymes break down food into nutrients that can be absorbed and used by the body.
   3. DNA replication: Enzymes like DNA polymerase ensure accurate copying of genetic material during cell division.