enzyme

Early observations of catalytic activity:
- Fermentation of fruit juices.
- Souring of milk.
- Spoiling of meat.
19th-century scientists discovered that some reactions occurring in natural conditions might not happen in artificial environments, such as test tubes.
Enzymes:
- Recognized as vital forces inseparable from living cells.
- Composed of protein molecules that show extraordinary catalytic power, surpassing synthetic catalysts.
- Exhibit a high degree of specificity in reactions.
- Function efficiently in dilute aqueous solutions under mild conditions (temperature and pH).
Approximately 2,000 known enzymes, but the focus will be on their properties and characteristics common across most.

By the end of this unit, you should be able to:

Discuss the general concept of chemical catalysis.
Describe the chemical nature of enzymes.
Enumerate different types of enzymes, and their nomenclature and examples.
Discuss factors affecting enzyme activity.
Explain enzyme kinetics, particularly using the Michaelis-Menten model.
Explain and illustrate how $K<em>M$ and $V</em>{max}$ characterize competitive and non-competitive inhibition.
Discuss the significance of coenzymes in living systems.
Provide examples of coenzymes.

Catalysts: Substances that speed up chemical reactions without altering the products formed in their absence.
- They lower the activation energy needed for reactions.
- Not consumed in the reaction and can be used repeatedly.
- Visualizing activation energy: Compared to riding over a hump in terrain, where finding a shortcut equates to the presence of a catalyst.

Enzymes serve as biological catalysts, hastening biochemical reactions.
- Increase reaction rates by lowering activation energy by about one million times.
- Example: Digestion of food would take approximately 50 years without enzymes present.

Naming enzymes involves identifying the substrate and the action performed:
- Example: For the reaction $RCH<em>2OH ightarrow RCHO + (coenzyme)-H</em>2$ , the enzyme is named: alcohol dehydrogenase (substrate = alcohol, action = dehydrogenation).
Enzyme structure:
- Can be simple (one polypeptide) or complex (multiple polypeptides and non-protein parts).
- Apoenzyme: The protein part.
- Coenzyme (or prosthetic group): Non-protein part.
- Together, they form a holoenzyme.
Some enzymes require metal ions (like $Mg^{2+}, Zn^{2+}, Fe^{3+}$ ) for activity, classified as activators or cofactors.
Zymogen: Inactive form of an enzyme, often secreted in this form (e.g., trypsinogen, pepsinogen).
Substrate: The molecule upon which the enzyme acts.

Enzymes display a high degree of specificity:
- Some act on a single type of substance (absolute specificity).
- Others act on a group of related substances (group specificity).
The International Union of Biochemists classifies enzymes into six major classes based on reaction types:
- These classes are documented along with their examples.

Active Site: The region of the enzyme that directly interacts with the substrate—a small portion of the enzyme's structure.
Lock and Key Model: Proposed by Emil Fischer, suggesting a precise fit between substrate and enzyme active site, akin to a key in a lock.
Induced Fit Model: Proposed by Daniel Koshland, represents a more flexible interaction where the enzyme's active site changes shape upon substrate binding to facilitate a stronger interaction.

Inhibitors: Chemicals that reduce enzyme activity, serving as tools for studying enzyme specificity and active site.
Types of Inhibition:
- Competitive Inhibition:
- Inhibitor competes for the active site; increasing substrate concentration can overcome inhibition.
- Examples include drug interactions like methotrexate and sulfa drugs acting against bacterial enzymes by mimicking substrates.
- Noncompetitive Inhibition:
- Inhibitor binds elsewhere on the enzyme, altering the active site and affecting enzyme activity regardless of substrate concentration.
- Heavy metals such as Hg^{2+}, Pb^{2+}, and Ag^{+} can act this way.
- Allosteric Regulation:
- Changes enzyme activity through the binding of a modulator molecule at an allosteric site, resulting in conformational changes; may act as either positive or negative effectors.

Vitamins (particularly B-vitamins) often act as coenzymes, essential for maintaining enzyme activity.
- These must be included in diets as the body cannot synthesize them.
- Lack of vitamins can lead to deficiency diseases.

Enzymes play a crucial role in catalyzing biological reactions, distinguished by specificity and efficiency within narrow pH and temperature ranges.
Reaction rates influenced by substrate concentration reflect saturation points (Vmax) and the Michaelis constant (Km).
Inhibitors, such as competitive and noncompetitive, affect enzyme activity, highlighting the importance of enzyme regulation.

Enzyme Practice: Label diagrams of enzyme activity.
Choose one of the following tasks:
- Create a brochure on enzymatic reactions.
- Summarize enzyme-driven reactions.
- Draw and label a graph demonstrating activation energy in relation to enzymes.

Define key terms and answer questions about enzyme concepts and behaviors in practical and clinical settings, including experimental illustration questions involving pH and temperature effects, competitive inhibitors, and allosteric regulation.

A list of academic texts and online resources for further reading, including journals and relevant articles.
Examples of videos on biochemical processes related to enzymes.