Practice Questions

While hydrogen bonds provide specificity, the planar, non-polar nitrogenous bases "stack" together via hydrophobic interactions to minimize their exposure to water. This base stacking is a major thermodynamic driving force for the stabilization of the DNA double helix.

A prosthetic group is a non-protein component that is covalently or very tightly, permanently bound to an enzyme. A coenzyme is an organic cofactor (often a vitamin derivative) that binds loosely and transiently. A zymogen is an inactive enzyme precursor.

During protein folding, hydrophobic R-groups tend to cluster in the protein's interior to avoid contact with the aqueous cellular environment (hydrophobic effect). Conversely, hydrophilic and charged R-groups are typically positioned on the surface where they can interact with water.

Human amylases are specific for the α-1,4 glycosidic bonds found in starch and glycogen. Cellulose consists of glucose monomers linked by β-1,4 glycosidic bonds, which requires the enzyme cellulase, an enzyme humans do not produce.

ATP is a modified nucleotide consisting of the nitrogenous base adenine, the sugar ribose, and three phosphate groups. The anhydride bonds between the phosphates are "high-energy" bonds, making ATP the primary energy currency of the cell.

Fibrous proteins (e.g., collagen, keratin) have long, chain-like, repetitive secondary structures that form strong, water-insoluble fibers. Their primary role is structural support, contrasting with the soluble, dynamic, roughly spherical nature of globular proteins like enzymes and antibodies.

Complementarity is the specific pairing dictated by hydrogen bonding potential: adenine pairs only with thymine (or uracil), and guanine pairs only with cytosine. This ensures a purine always pairs with a pyrimidine, maintaining a consistent double helix structure.

Amphipathic molecules have a dual nature. Phospholipids are a prime example, with a hydrophilic polar "head" (phosphate group) and hydrophobic non-polar "tails" (fatty acid chains). This property is fundamental to the formation of lipid bilayers in water.

Phosphorylation is a key reversible covalent modification used to regulate enzyme activity. A kinase adds a phosphate group, causing a shape change that can activate or deactivate the enzyme. A phosphatase removes it, reversing the effect.

A non-competitive inhibitor reduces the total amount of functional enzyme, thereby lowering the Vmax. Since the inhibitor does not bind to the active site, increasing the substrate concentration cannot saturate the inhibitor and restore Vmax to its original level.