1.5.3 Enzymes

• What are enzymes and their role in biological reactions?

  Biological catalysts
• Each enzyme is specific to certain substrates
• What is the primary structure of an enzyme?

  Amino acid sequence
• Secondary structure of enzymes arises from hydrogen bonds.
• Match the tertiary structure bond with its description:

  Hydrogen bond ↔️ Weak attraction between molecules

  Disulfide bond ↔️ Strong covalent bond between sulfur atoms

  Ionic bond ↔️ Attraction between oppositely charged ions

  Hydrophobic bond ↔️ Interaction between nonpolar regions
• The region within an enzyme where substrates bind is called the active site
• What is the enzyme-substrate complex?

  Temporary reactive intermediate
• The enzyme-substrate complex lowers activation energy to facilitate catalysis.
• How do enzymes lower activation energy in biological reactions?

  By acting as catalysts
• Lactase breaks down lactose into glucose and galactose
• Arrange the levels of enzyme structure in order from simplest to most complex:

  1️⃣ Primary

  2️⃣ Secondary

  3️⃣ Tertiary

  4️⃣ Quaternary
• What are the two models that describe enzyme-substrate interactions?

  Lock-and-key and induced fit
• The lock-and-key model describes enzymes with rigid active sites.
• Which enzyme changes its shape to accommodate glucose in the induced fit model?

  Hexokinase
• The region within an enzyme crucial for lowering activation energy is the active site
• The active site of an enzyme is crucial for lowering the activation energy of reactions.
• Enzymes are proteins with four levels of structure.
• Match the enzyme structure level with its description:

  Primary ↔️ Linear sequence of amino acids

  Secondary ↔️ Folding into alpha helices and beta pleated sheets

  Tertiary ↔️ 3D structure maintained by various bonds

  Quaternary ↔️ Arrangement of multiple polypeptide subunits
• The enzyme-substrate complex forms when an enzyme binds to its substrate at the active site.
• The formation of the enzyme-substrate complex lowers the activation energy.
• Order the steps in the enzyme-substrate reaction:

  1️⃣ Enzyme binds to substrate

  2️⃣ Enzyme-substrate complex forms

  3️⃣ Product is released
• In the lock-and-key model, the binding mechanism is static and rigid.
• The induced fit model is more realistic than the lock-and-key model.
• Match the factor affecting enzyme activity with its effect:

  Temperature ↔️ Increases activity up to optimal, then decreases

  pH ↔️ Peaks at optimal pH; deviating reduces activity

  Enzyme concentration ↔️ Increases activity if substrate is not limiting

  Substrate concentration ↔️ Increases activity until saturation
• Excessive heat can cause enzyme denaturation, reducing its activity.
• Enzyme activity decreases if the pH deviates from its optimal value.
• Match the type of enzyme inhibitor with its mechanism:

  Competitive ↔️ Binds to the active site, preventing substrate binding

  Non-competitive ↔️ Binds to a site other than the active site, altering enzyme shape
• Methotrexate is an example of a competitive inhibitor.
• What are enzyme inhibitors?

  Substances reducing enzyme activity
• Competitive inhibitors bind to the active site of the enzyme.
• Non-competitive inhibitors affect Vmax but not Km.
• What is an example of a non-competitive inhibitor?

  Doxycycline
• Match the type of cofactor/coenzyme with its description:

  Cofactors ↔️ Inorganic ions that stabilize enzyme structure

  Coenzymes ↔️ Organic molecules that carry chemical groups
• What are cofactors and coenzymes?

  Non-protein enzyme assistants
• Cofactors are inorganic ions that bind to the enzyme and stabilize its structure.
• Coenzymes are often derived from vitamins.
• What is an example of a cofactor used by cytochrome c oxidase?

  Copper and iron
• Order the levels of protein structure in enzymes from simplest to most complex:

  1️⃣ Primary

  2️⃣ Secondary

  3️⃣ Tertiary

  4️⃣ Quaternary
• The primary structure of an enzyme consists of a linear sequence of amino acids.
• What type of bonds maintain secondary structures in enzymes?

  Hydrogen bonds