Enzymes and Catalysts Quiz

Enzymes

• Enzymes are biological catalysts, speeding up reactions without being consumed.
• They provide an alternative pathway with lower activation energy.
• Living systems use enzymes as catalysts.
• Most enzymes are water-soluble, globular proteins.
• Enzymes function as biological catalysts.
• Most enzymes are highly specific, recognizing only one specific substrate or type of substrate.

Intended Learning Outcomes

• Students will describe the structure of enzymes.
• Students will explain activation energy.
• Students will describe factors affecting enzyme action.
• Students will recognise enzyme function in different areas of the human body.

Catalysts

• A catalyst accelerates a reaction without being used up by the reaction.
• Catalysts offer an alternative reaction pathway with reduced activation energy.

Enzyme Names

• Enzyme names typically end in "-ase."
• Common digestive enzyme names end in "-in" (e.g., pepsin, trypsin).
• Some enzyme names incorporate the substrate (e.g., sucrase).
• Enzyme names can also describe their function (e.g., oxidase, hydrolase).

Enzymes Lower Activation Energies

• Enzymes function by forming complexes with substrates, stabilizing them and decreasing activation energy.
• E + S → ES → P (Enzyme + Substrate → Enzyme-Substrate complex → Product).
• Reaction rates can increase by a factor of 10⁶ - 10¹² with enzymes.

Energy for Activation

• Energy for reactions comes from the hydrolysis of adenosine triphosphate (ATP).
• ATP + H₂O → ADP + P_i + energy

Enzyme Shape and Reactivity

• The active site is a specific region on an enzyme's surface with a unique shape.
• Enzyme recognition occurs when a substrate fits the active site shape.
• Intermolecular interactions between the substrate and amino acid side chains within the active site are crucial.

Fischer “Lock and Key” Model

• Substrate-enzyme binding resembles a key fitting into a lock.
• Only one type of substrate fits into an enzyme's active site.
• An enzyme-substrate complex forms, mediating the catalyzed reaction.

Induced-Fit Model

• A more advanced model.
• The active site's shape changes slightly when a substrate binds.
• The conformational change enhances the fit of the substrate.
• A more perfect substrate-enzyme fit is achieved.
• Substrate binds to active site and enzyme changes shape.

Catalytic Cycle of an Enzyme

• Substrates bind to the active site, creating an enzyme-substrate complex.
• The complex undergoes internal rearrangements, forming products.
• The enzyme releases the reaction's products.

Factors Affecting Enzyme Activity

• Enzyme activity depends on three factors:
  • The enzyme's three-dimensional structure (anything affecting structure affects function).
  • Substrate and enzyme concentration.
  • Interactions with other molecules (inhibition or regulation occurring at the active site or elsewhere on the protein surface).

Enzyme Activity - Enzyme Structure

• Enzyme structure is governed by weak intermolecular interactions controlling tertiary structure.
• Changes affecting tertiary structure affect enzyme activity.

Enzyme Activity - Effect of Temperature

• Low temperatures result in slow enzyme activity.
• Molecules collide less frequently due to lower speeds.
• Insufficient energy to overcome activation energy.
• Activity increases up to an optimum temperature.
• Molecules move faster and collide more.
• Above the optimum temperature (over 40°C), many enzymes denature.

Enzyme Activity - Effect of pH

• Most enzymes operate within a narrow pH range.
• Large changes in pH can denature enzymes.
• Disrupt the precise three-dimensional arrangements of proteins.
• Smaller pH changes affect substrate and/or enzyme side chain ionization.