Classification of enzymes | Biomolecules | Biology | Khan Academy

Summary

This video script delves into enzyme nomenclature and their classification into six main categories: oxidoreductases, transferases, hydrolases, lyases, isomerases, and ligases. It explains the historical development of enzyme naming, starting with the suffix '-ase' and evolving to more descriptive names indicating the reactions they catalyze. The script uses examples like lactate dehydrogenase and alanine transaminase to illustrate how enzymes function in biochemical pathways, aiming to demystify the complex world of enzymes and make it more accessible and interesting.

Takeaways

• 🔬 Enzymes are biocatalysts that speed up chemical reactions in the body.
• 📝 Traditional enzyme names often end with the suffix -ase, indicating their catalytic function.
• 🔍 The naming of enzymes was historically inconsistent, leading to confusion among scientists.
• 🌐 The International Union of Biochemistry established the International Commission on Enzymes to standardize enzyme naming.
• 📚 Enzymes are classified into six main classes: oxidoreductases, transferases, hydrolases, lyases, isomerases, and ligases.
• ⚔️ Oxidoreductases catalyze both oxidation and reduction reactions, such as lactate dehydrogenase in lactic acid fermentation.
• ✂️ Transferases transfer functional groups from one molecule to another, exemplified by alanine transaminase.
• 💧 Hydrolases catalyze hydrolysis reactions, breaking molecules with the addition of water, like pyrophosphatase.
• ⚡️ Lyases catalyze the removal of groups from substrates without hydrolysis or oxidation, such as pyruvate decarboxylase.
• 🔄 Isomerases catalyze the rearrangement of atoms to form isomers, like aldose reductase.
• 🔗 Ligases join two molecules with the help of ATP, an example being DNA ligase.
• 📘 Studying specific biochemical pathways, like the Krebs cycle or glycolysis, can help in understanding the role of enzymes in cellular processes.

Q & A

What are enzymes and what role do they play in the body?

Enzymes, also known as biocatalysts, are proteins that speed up the rate of chemical reactions inside the body without being consumed in the process.

Why were enzymes initially named with an 'ase' suffix?

The 'ase' suffix in enzyme names originated as a way to honor the scientist who first discovered an enzyme, diastase. Subsequent enzymes were named using this suffix as a convention.

What is the limitation of the initial enzyme naming system using the 'ase' suffix?

The initial naming system did not provide information about the reaction the enzyme catalyzes, making it difficult to understand the enzyme's function just by its name.

How did scientists begin to incorporate more information about enzyme function into their names?

Scientists started to name enzymes with a hint of the reaction they catalyze, such as 'glucose oxidase', which indicates the substrate and the type of reaction.

What was the purpose of the International Union of Biochemistry in establishing the International Commission on Enzymes?

The International Commission on Enzymes was established to classify and standardize enzyme naming, addressing the confusion and chaos caused by the lack of specific rules for naming enzymes.

What are the six classes of enzymes as classified by the International Commission on Enzymes?

The six classes of enzymes are oxidoreductases, transferases, hydrolases, lyases, isomerases, and ligases.

What type of reaction is catalyzed by oxidoreductases?

Oxidoreductases catalyze reactions involving both oxidation (gain of oxygen, loss of electrons, or loss of hydrogen) and reduction (loss of oxygen, gain of electrons, or gain of hydrogen).

Can you give an example of an oxidoreductase and the reaction it catalyzes?

Lactate dehydrogenase is an example of an oxidoreductase that catalyzes the conversion of lactate to pyruvate by oxidizing lactate and reducing NAD+ to NADH.

What is the function of transferases in enzymatic reactions?

Transferases catalyze the transfer of functional groups from one molecule (the donor) to another (the acceptor), often requiring the input of energy.

How do hydrolases contribute to biological systems?

Hydrolases catalyze the breakdown of various types of bonds in the presence of water, playing a crucial role in digestion and the metabolism of molecules.

What is the primary action of lyases?

Lyases catalyze the removal of groups from their substrates without hydrolysis or oxidation, often resulting in the formation of double bonds.

What is the role of isomerases in enzymatic reactions?

Isomerases catalyze the rearrangement of atoms within a molecule to form isomers, which are molecules with the same molecular formula but different geometric arrangements or functional group positions.

How do ligases function in biological processes?

Ligases catalyze the joining of two molecules, often using energy from ATP hydrolysis, to form larger molecules or repair breaks in macromolecules like DNA.

What is a practical way to study enzymes and understand their functions in living cells?

Studying the chemical reactions that occur in living cells, such as the Krebs cycle or glycolysis, and analyzing the role of enzymes at each step can help in understanding their functions and classifications.