Chapter 3.1 - Enzyme Structure and Mode of Action | Cambridge A-Level 9700 Biology

Summary

In this lecture on enzymes, key concepts such as enzyme structure, specificity, and mode of action are discussed. Enzymes are biological catalysts that speed up reactions by lowering activation energy. The structure of enzymes is globular, with a precise active site where substrates bind, ensuring specificity. The induced fit model is highlighted, showing how enzymes flexibly adjust to fit substrates. Enzymes can work both intracellularly and extracellularly, and they remain unchanged after catalyzing reactions. This process is crucial for regulating metabolism and accelerating biochemical reactions in living organisms.

Takeaways

• 😀 Enzymes are biological catalysts that speed up chemical reactions in the body by lowering activation energy.
• 😀 Enzymes are highly specific, with each enzyme binding to only one or a few substrates.
• 😀 Enzymes remain unchanged after a reaction, allowing them to catalyze many reactions with a small amount.
• 😀 Enzymes have a high turnover number, meaning they can catalyze many reactions per unit of time.
• 😀 Enzymes can either synthesize new compounds or break them down in metabolic reactions.
• 😀 The activation energy is the energy needed to start a chemical reaction, and enzymes lower this energy barrier.
• 😀 All enzymes are globular proteins, mostly with tertiary structures, some with quaternary structures.
• 😀 The active site of an enzyme is where the substrate binds, and its shape is complementary to the substrate.
• 😀 The lock and key model suggests the active site is rigid and fits perfectly with the substrate, but the induced fit model is more accurate, suggesting the active site molds around the substrate.
• 😀 Enzymes can function both intracellularly (inside cells) and extracellularly (outside cells).
• 😀 Enzymes catalyze reactions by forming an enzyme-substrate complex, lowering activation energy, and enabling the formation of products.

Q & A

What is the main function of enzymes in the body?

Enzymes act as biological catalysts that speed up chemical reactions in the body, either by synthesizing new compounds or breaking down existing ones.

What does it mean when we say enzymes are 'specific'?

Enzymes are specific in that each enzyme can only bind to one or a few substrates that fit its active site, and it does not bind to others.

How do enzymes catalyze reactions?

Enzymes catalyze reactions by lowering the activation energy required for the reaction to occur, making it easier for reactants to be converted into products.

What is activation energy, and how is it related to enzymes?

Activation energy is the energy needed for a chemical reaction to begin. Enzymes lower this energy barrier, making reactions occur more quickly and with less input energy.

What is the difference between an uncatalyzed and a catalyzed reaction in terms of activation energy?

In an uncatalyzed reaction, the activation energy is high, while in a catalyzed reaction, enzymes reduce the activation energy required, facilitating a quicker reaction.

What is the basic structure of an enzyme?

Enzymes are globular proteins with a specific 3D structure, often composed of tertiary or quaternary structures. Their active sites are where substrates bind.

What role does the active site play in enzyme function?

The active site is the region where the substrate binds to the enzyme. The shape of the active site determines the enzyme's specificity for a particular substrate.

What is the lock and key model of enzyme action?

The lock and key model suggests that the enzyme's active site is perfectly shaped to fit the substrate, without any change in the active site's shape.

How does the induced fit model differ from the lock and key model?

The induced fit model suggests that the enzyme's active site is flexible and molds around the substrate, providing a better fit during the reaction, unlike the rigid fit described by the lock and key model.

Where do enzymes typically operate in the cell?

Enzymes can operate both inside the cell (intracellular) and outside the cell (extracellular), such as in lysosomes or secreted to the outside, like lysozyme in tears.

What is the process that leads to the formation of an enzyme-substrate complex?

The enzyme and substrate collide with the correct orientation and sufficient energy, allowing the enzyme's active site to bind to the substrate, forming an enzyme-substrate complex.

How does enzyme activity lead to product formation?

The enzyme-substrate complex forms, causing the substrate to undergo chemical changes, breaking or forming bonds more easily, lowering activation energy and allowing products to form while the enzyme remains unchanged.