What is the role of activation energy in enzyme-catalyzed reactions?

Activation energy is the minimum amount of energy required for a reaction to proceed. Enzymes lower this activation energy by providing an alternate reaction pathway, enabling reactions to occur faster and using less energy. This catalytic function allows biological processes to happen efficiently at body temperature without requiring excessive heat or energy input.

How does an enzyme's active site determine which substrates it can bind?

Each enzyme's active site has a specific shape and chemical properties that match only certain substrates. When the correct substrate enters the active site, the enzyme changes shape to achieve higher affinity, facilitating the reaction. The enzyme then releases the products and returns to its original shape, ready to repeat the catalytic cycle with new substrate molecules.

What is the difference between catabolic and anabolic enzymes?

Catabolic enzymes break down larger molecules into multiple smaller products, such as lactase splitting lactose into glucose and galactose. Anabolic enzymes combine multiple substrates into a single larger product, like DNA polymerase joining nucleotides to synthesize DNA. These opposing functions allow organisms to both extract energy and build complex molecules.

How do pH and temperature affect enzyme activity?

Enzymes require specific pH and temperature ranges to function optimally. Deviations from optimal pH alter the charges in the active site, preventing substrate interaction. Similarly, temperature shifts alter the active site shape; returning to optimal temperature usually restores function, but excessive heat can permanently denature the enzyme. These properties are exploited in food preservation through pickling and cooking.

What are cofactors and coenzymes, and why do some enzymes need them?

Cofactors are inorganic substances like ions (Mg2+, Mn2+) required for enzymatic function, while coenzymes are organic biomolecules like B vitamins that participate in catalysis without being consumed. Some enzymes cannot catalyze reactions independently and require these helper molecules to function. For example, vitamin C is an essential coenzyme for collagen synthesis.

How is enzyme reaction rate measured and used as a reference in experiments?

Reaction rate is quantified by measuring the amount of product made per unit time, calculated during the linear phase when product concentration increases steadily until enzyme saturation. Once a baseline reaction rate is established under standard conditions, it serves as a control reference point for comparing how different treatments like temperature or pH variations affect enzyme efficiency.

What are enzyme inhibitors and how do they affect enzyme function?

Enzyme inhibitors are molecules that decrease enzymatic activity by binding to the active site or allosteric sites on the enzyme. Inhibitor binding can be reversible, allowing the enzyme to resume function once the inhibitor detaches, or irreversible, permanently damaging the enzyme. Inhibitors have practical applications as antibiotics to inhibit bacterial growth and as chemotherapeutics to prevent cancer cell division.

Enzyme Activity

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European explorers had adequate knowledge, skills and equipment, but why didn't they reach the New World until the end of the 15th century? You'll be surprised to learn that the answer to this question is related to the small biological molecules called enzymes, that act as catalysts.

What is a catalyst? It is a substance that enables a reaction to occur faster, using less energy. If you plotted a graph of the energy needed for an uncatalyzed biological reaction, it would look something like this. This height represents the activation energy, which is the minimum amount of energy needed for the reaction to proceed. Enzymes, working as a catalyst, provide an alternate reaction pathway, with a lower activation energy.

So, how do enzymes actually work? Most enzymes are proteins. The part of their structure which interacts with the molecules they catalyze, is called the active site, which has affinity for only certain substrates and won't bind with others. When the correct substrates enter the active site, the enzyme changes its shape to attain a higher affinity configuration. This transition state facilitates the reaction and converts the reactants into products. The enzyme, however, has a lower affinity for the products so it releases them and returns to its original shape, ready to repeat the same process. This is an example of a catabolic enzyme because it took a single substrate and broke it to form multiple products. The opposite of this, is the anabolic enzyme, which takes two substrates and joins them together to make a larger product.

There are numerous other ways that enzymes function. For instance, this enzyme transfigures a single substrate into a new shape. Whereas this one, transfers part of one substrate, onto another. Some enzymes cannot catalyze reactions on their own and require cofactors or coenzymes in order to catalyze their reaction.

So, you might be wondering, how does all this relate to the 15th century voyages? At that time, sailors didn't have access to fresh produce containing vitamin C, a coenzyme essential for collagen synthesis. Because of that, the sailors would develop scurvy, a vitamin C deficiency disease, which was often fatal. They solved this problem by pickling vitamin C-rich fruits and vegetables. Pickling reduced the pH of the food, which prevented the activity of microbial enzymes, responsible for rotting them. Therefore, destruction of microbial enzymes and the saving of an essential coenzyme, played a major role in the success of long expeditions.

In this lab, you can quantify how different conditions affect enzyme function, by assessing the reaction rate, the amount of product made, per unit time. You'll first measure the baseline reaction rate at a standard room temperature and neutral pH. The rate will increase at the beginning until all of the enzyme molecules are completely saturated with the substrate. And then, the catalysis will reach a steady level as the enzymes are busy continuing the cycle of binding substrate, catalysis and release. Once the baseline reaction rate has been established, it can be used as reference point for other conditions. The enzyme that you'll work with in this lab is turnip peroxidase. You'll evaluate its activity under varying values of temperature and pH.