Bioquímica - Aula 05 - Enzimas

Summary

This video lecture, presented by Professor Ângelo Cortalas, explores the fascinating world of enzymes, which are essential biological catalysts for organic reactions. Enzymes speed up reactions by lowering activation energy, making metabolic processes more efficient. The lecture delves into enzyme structure, with a focus on the active site, and explains how temperature, pH, and cofactors influence enzyme activity. The importance of enzyme specificity and the role of cofactors like vitamins is also discussed. Furthermore, the lecture touches on enzyme classes, isoenzymes, and the concept of zymogens, emphasizing their role in metabolism and cell function.

Takeaways

• 😀 Enzymes are biological catalysts that speed up organic reactions by lowering activation energy, which is necessary for metabolic processes.
• 😀 Catalysts, including enzymes, increase the rate of chemical reactions without altering the reactants or products, by lowering the activation energy required for reactions.
• 😀 Enzymes are mostly proteins, and their discovery dates back to the early 19th century. In the 1850s, they were referred to as 'ferments'.
• 😀 The activation energy of a reaction can be lowered by enzymes, allowing more molecules to react and increasing the speed of the reaction by billions of times.
• 😀 Enzymes have an active site that binds with a specific substrate, forming an enzyme-substrate complex that facilitates the reaction.
• 😀 The enzyme-substrate interaction is often compared to a 'lock and key' mechanism, where the enzyme's active site is specific to its substrate.
• 😀 Changes in pH and temperature can affect enzyme activity. Extreme pH or temperatures can alter the enzyme's structure, reducing its efficiency.
• 😀 Enzymes have an optimal pH and temperature at which they function most efficiently, which varies for different enzymes depending on their environment.
• 😀 Cofactors, such as metal ions or organic molecules, are required by some enzymes to be functional. These non-protein components are called cofactors and coenzymes.
• 😀 Some enzymes are produced in an inactive form called zymogens, which are activated through modifications outside the cell. Examples include pepsinogen, trypsinogen, and chymotrypsinogen.
• 😀 Isoenzymes are multiple forms of the same enzyme, which result from different genes or alleles, while isoforms are variations that occur after protein translation and affect enzyme function.

Q & A

What are enzymes and why are they important in biochemical reactions?

Enzymes are biological catalysts that speed up the rate of chemical reactions without being consumed in the process. They are crucial in biochemical reactions because they allow processes in the body to occur at a viable pace, particularly when organic molecules are large and reactions would otherwise be too slow.

What is the concept of activation energy in chemical reactions?

Activation energy is the minimum energy required for a chemical reaction to occur. It is the energy needed to break bonds in reactants to form products. Enzymes lower the activation energy, enabling more molecules to react and increasing the reaction rate.

How do enzymes reduce the activation energy of a reaction?

Enzymes reduce the activation energy by forming a temporary complex with the substrate, called the enzyme-substrate complex. This complex stabilizes the transition state, lowering the energy required for the reaction to proceed.

What is the 'active site' of an enzyme?

The active site of an enzyme is the specific region of the enzyme where the substrate binds. It has a unique shape that allows it to interact specifically with the substrate, facilitating the chemical reaction.

How do temperature and pH affect enzyme activity?

Both temperature and pH influence enzyme activity by affecting the enzyme's structure. High temperatures or extreme pH levels can alter the enzyme's shape, potentially reducing its ability to bind to the substrate. Each enzyme has an optimal temperature and pH at which it functions most efficiently.

What are cofactors and coenzymes in enzymatic reactions?

Cofactors are non-protein chemical compounds that assist enzymes in their function. They can be metal ions like magnesium or zinc. Coenzymes are organic molecules that bind to enzymes and are necessary for their activity, often derived from vitamins (e.g., vitamin B complexes).

What is the difference between a holoenzyme and an apoenzyme?

A holoenzyme is the complete, functional enzyme, including its protein portion (apoenzyme) and any necessary cofactors or coenzymes. An apoenzyme is the enzyme without its cofactors or coenzymes, rendering it inactive.

What are zimogens (or proenzymes), and why are they important?

Zymogens are inactive enzyme precursors. They are synthesized in an inactive form to prevent them from breaking down cellular components. Once they reach their activation site, they undergo structural changes to become active enzymes. An example is pepsinogen, which activates to pepsin in the stomach.

What are isoenzymes and how do they differ from isoforms?

Isoenzymes are enzymes that catalyze the same reaction but are derived from different genes or gene loci, meaning they are molecularly different. Isoforms, on the other hand, are different forms of the same enzyme that result from post-translational modifications after the enzyme is synthesized.

What is the significance of enzyme specificity in catalysis?

Enzyme specificity ensures that only certain substrates can bind to the enzyme's active site. This specificity is vital for proper metabolic control, as it prevents undesired reactions and ensures that the correct products are formed from the correct reactants.