MCQs

This self-assembly is an entropically driven process. When phospholipids are mixed with water, they spontaneously arrange into bilayers or micelles to bury their hydrophobic fatty acid tails away from water, while the polar head groups interface with the aqueous environment.

An enzyme's catalytic function is entirely dependent on the specific 3D shape of its active site. Denaturation by heat, pH, or chemicals disrupts the weak bonds maintaining the tertiary structure, causing the active site to lose its precise conformation, preventing substrate binding.

The extensive branching of glycogen creates many non-reducing ends. Multiple glycogen phosphorylase enzymes can act simultaneously on these ends, allowing for a very rapid release of glucose monomers to meet high metabolic demands, particularly in muscles.

Coenzymes are organic carrier molecules that participate directly in the reaction. NAD+, for example, accepts a hydride ion (H⁻) to become NADH, effectively acting as an electron carrier. It is chemically changed during the reaction and must be regenerated. An enzyme cannot alter the reaction's equilibrium constant.

Cis-double bonds in unsaturated fatty acids create kinks that prevent the molecules from packing closely together. This reduces the intermolecular van der Waals forces, resulting in a lower melting point and a liquid state (oil) at room temperature.

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.

The test detects the free carbonyl group (C=O) at the anomeric carbon of a reducing sugar. This group can be oxidized, thereby reducing the Cu²⁺ in Benedict's reagent to Cu⁺, forming a colored precipitate. Non-reducing sugars lack this free group.

Quaternary structure exists only in proteins composed of more than one polypeptide chain (subunit). It describes the specific 3D arrangement and interactions between these individual, folded subunits, as seen in hemoglobin (α2β2).

Condensation (or dehydration synthesis) is the anabolic process where monomers are covalently bonded together with the simultaneous removal of a water molecule. This is the fundamental mechanism for polymer formation. Hydrolysis is the reverse, catabolic process.

Both glycogen and cellulose are glucose polymers, but glycogen has α-1,4 and α-1,6 glycosidic bonds, allowing it to be a branched, digestible energy source. Cellulose has β-1,4 glycosidic bonds, which create straight chains that form strong structural fibers and are indigestible by most animals.