Enzyme Structure and Function Quiz

Enzyme Structure and Function

• Enzymes are biological catalysts, speeding up biochemical reactions like respiration and photosynthesis.
• They are synthesized inside living cells; some enzymes are extracellular, functioning outside the cell, while others are intracellular, functioning inside the cell.
• Enzymes are mostly globular proteins, but some are RNA molecules called ribozymes.
• Enzymes remain unchanged at the end of a reaction.
• The substrate is the substance acted upon by an enzyme.
• Once a reaction occurs, the enzyme-substrate complex breaks into products and the enzyme, which continues to catalyze.

Enzyme Classifications

• Transferases: Catalyze the transfer of atoms or groups from one molecule to another. Example: transamination.
• Hydrolases: Catalyze hydrolytic reactions (and their reverse), involving the breaking or forming of bonds using water. Example: breaking down a disaccharide.
• Lyases: Catalyze elimination or addition reactions, often breaking or forming double bonds. Example: fermentation of sugar by yeast.
• Isomerases: Catalyze the rearrangement of atoms within a molecule, forming isomers. Example: glucose 1-phosphate to glucose 6-phosphate.
• Ligases: Catalyze the joining of two molecules, often using energy from ATP. Example: a reaction in protein synthesis.
• Oxidoreductases: Involved in redox reactions, including dehydrogenases, oxidases, and peroxidases. These enzymes transfer hydrogen atoms, oxygen atoms, or electrons. Example: oxidation reaction in anaerobic respiration in yeast.

Enzyme Properties

• Enzymes are highly specific, reacting with only one or similar substrates.
• They catalyze reactions by lowering the activation energy.
• Enzymes can be used repeatedly in similar reactions.
• The enzyme itself is not changed by the reaction.
• They speed up reaction rates, but do not change the products or properties of the final products
• Reaction rates are influenced by concentration of both enzyme and substrate, temperature, pH, and inhibitors.

Mechanism of Enzyme Action

• Active Site: A specific region on the enzyme where the substrate binds. Its complementary shape and chemical properties are crucial for substrate binding.
• Induced Fit: The active site’s shape changes slightly upon substrate binding; this improves the efficiency of the reaction.
• Lock and Key: Substrate fits perfectly into the active site, like a key into a lock.
• Enzymes often lower the activation energy needed for a reaction to proceed by forming transient interactions with the substrate. This allows the substrate to overcome an energy barrier, leading to the formation of the product.
• At the active site, bonds of the substrate (reactant) are broken or formed, resulting in a changed shape of the product. The product then detaches from the enzyme allowing it to be used again.
• The enzyme is not permanently altered or consumed.

Activation Energy

• The energy required for a reaction to occur.
• Enzymes lower the activation energy, allowing reactions to occur more quickly at lower temperatures.

Cell Theory

• Basic structural and functional unit of all living things is the cell.
• All organisms are made up of cells.
• All cells arise from pre-existing cells.