Biology Enzymes and Their Functions

Enzymes

• Enzymes are biological catalysts, increasing the speed of chemical reactions without being consumed by the reaction, speeding up metabolic reactions.
• Most enzymes are proteins.
• Each enzyme acts on a specific substrate.

Enzyme-Substrate Complex

• Enzymes function by forming an unstable intermediate complex with the substrate (the substance acted upon).
• When the enzyme-substrate complex (ES complex) breaks down, the product is released, and the original enzyme is regenerated, ready to form a new ES complex.
• Every enzyme is characterized by one or more active sites. These are regions where the substrate binds to form the enzyme-substrate complex.

Induced Fit

• Enzyme shape isn't exactly complementary to the substrate.
• Substrate binding causes a change in the enzyme's shape known as induced fit.
• Induced fit helps break and form bonds.

Enzyme Naming

• Scientists often add the suffix -ase to the name of the substrate to name enzymes.
  • Example: Sucrase acts on sucrose, maltase acts on maltose.

Enzyme Specificity

• Enzymes are specific; a specific enzyme for each substrate.
• The enzyme urease decomposes urea to ammonia and carbon dioxide, not other substrates.
• Sucrase splits only sucrose.

Co-factors

• Some enzymes consist solely of proteins (apoenzymes).
• Other enzymes have additional components (cofactors): organic or inorganic molecules (eg Mg, Ca ions) that are needed to help the enzyme function.
• Neither apoenzyme nor cofactor alone has catalytic activity; only when combined does the enzyme function properly.
• A cofactor that is organic and non-polypeptide is a coenzyme.
• Many vitamins are coenzymes or parts of coenzymes.

Optimal Temperature

• Each enzyme has an optimal temperature for the fastest reaction rate.
• Enzymatic activity increases with temperature up to an optimal point.
• At lower temperatures, enzymatic reactions proceed slowly or not at all; enzymes are inactive at 0°C.
• In humans, the optimal temperature is between 35-40°C.
• Above 50°C, human enzymes are destroyed (denatured).
• Heat-tolerant bacteria and archaea have different optimal temperatures (70-80°C).

Optimal pH

• Most enzymes operate within a narrow pH range with an optimal pH for their fastest reaction rate.
• Optimal pH in most human enzymes is between 6 and 8.
  • Example: Pepsin (acid medium, pH 2) is a protein-digesting enzyme in the stomach.
  • Example: Trypsin (basic medium, pH 8) is an enzyme splitting proteins in the small intestine.
  • Example: Salivary amylase (neutral pH 7) acts on starch.

Activation Energy

• All reactions need activation energy (energy needed to break existing bonds and start a reaction).
• Enzymes lower activation energy requirement, speeding up reactions.
• The graph shows how enzymes reduce the energy barrier to start a reaction.

Enzyme and Substrate Concentration

• Enzyme activity is regulated.
• Constant pH and temperature, reaction rate depends on concentrations of enzyme and substrate.
• Rate increases proportionally to enzyme concentration, if substrate is in excess.
• If enzyme concentration is high, then rate is proportional to substrate concentration, until the enzymes are saturated.

Enzyme Inhibition

• Reversible inhibition: An inhibitor forms weak bonds with the enzyme.
  • Competitive inhibition: The inhibitor competes with the substrate for the active site.
  • Noncompetitive inhibition: The inhibitor binds to a site other than the active site, changing the enzyme's shape so it cannot bind to the substrate.
• Irreversible inhibition: The inhibitor combines with the enzyme and permanently inactivates it. (e.g., mercury, lead).

Evaluation

• A is the substrate; E is the product; C is the enzyme.

Explore the fascinating world of enzymes, their role as biological catalysts, and how they interact with substrates. This quiz covers the enzyme-substrate complex, the concept of induced fit, and common naming conventions for enzymes. Test your knowledge of these essential proteins and their functions in metabolic reactions.