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 primary structure of an enzyme is the linear sequence of amino acids.
• Secondary structures of enzymes include alpha helices and beta pleated sheets.
• The tertiary structure of an enzyme is maintained by hydrogen, ionic, disulfide, and hydrophobic bonds.
• Quaternary structures of enzymes involve the arrangement of multiple polypeptide subunits.
• What is the region on an enzyme where substrates bind called?

  Active site
• The active site of an enzyme is crucial for lowering the activation energy of reactions.
• Enzymes, being proteins, have four levels of structure.
• Match the enzyme structure level with its bonding:

  Primary ↔️ Peptide bonds

  Secondary ↔️ Hydrogen bonds

  Tertiary ↔️ Hydrogen, ionic, disulfide, hydrophobic bonds
• Steps in the formation of the enzyme-substrate complex

  1️⃣ Enzyme and substrate combine at the active site

  2️⃣ Bonds such as hydrogen bonds and hydrophobic interactions form

  3️⃣ Activation energy is lowered

  4️⃣ Catalysis is facilitated
• What are the two models that describe enzyme-substrate interaction?

  Lock-and-key and induced fit
• Match the enzyme-substrate interaction model with its description:

  Lock-and-key ↔️ The active site precisely fits the substrate

  Induced fit ↔️ The active site changes shape to fit the substrate
• Enzyme activity is affected by temperature, pH, enzyme concentration, and substrate concentration.
• Enzyme activity increases with temperature up to the optimal temperature, then decreases due to denaturation.
• At what pH does enzyme activity peak?

  Optimal pH
• Increasing enzyme concentration always increases enzyme activity.

  False
• Excessive heat causes enzyme denaturation, reducing its activity.
• What are enzyme inhibitors?

  Substances that reduce activity
• Match the type of enzyme inhibitor with its effect on Vmax and Km:

  Competitive ↔️ Decreases Vmax, increases Km

  Non-competitive ↔️ Decreases Vmax, Km unchanged
• Non-competitive inhibitors bind to the active site of the enzyme.

  False
• What are enzyme inhibitors?

  Substances that reduce activity
• Competitive inhibitors bind to the active site of an enzyme.
• Non-competitive inhibitors affect enzyme activity without binding to the active site.
• Match the cofactors and coenzymes with their functions:

  Cofactors ↔️ Stabilize enzyme structure

  Coenzymes ↔️ Carry chemical groups
• Which vitamin is NAD+ derived from?

  Vitamin B3
• Order the four levels of protein structure in enzymes:

  1️⃣ Primary

  2️⃣ Secondary

  3️⃣ Tertiary

  4️⃣ Quaternary