Practice Questions

A longer saturated hydrocarbon chain has a greater surface area for van der Waals interactions with neighboring chains, requiring more thermal energy (higher temperature) to disrupt these interactions and melt. Unsaturation, conversely, introduces kinks that lower the melting point.

Except for methionine and tryptophan, all 18 other amino acids are encoded by 2 to 6 synonymous codons. This property is called degeneracy and provides a buffer against the harmful effects of point mutations.

The conformational change of the enzyme upon substrate binding physically distorts the substrate molecule. This "strain" on specific bonds makes them less stable and closer to the transition state, thereby reducing the energy required to break them (the activation energy).

Histones are basic proteins that associate with and neutralize the negative charge of the DNA phosphate backbone. The DNA wraps around an octamer of histone proteins to form a nucleosome, the fundamental unit of chromatin packaging, allowing the long DNA molecule to be compacted.

Zymogens (like pepsinogen to pepsin) are activated by the irreversible hydrolytic cleavage of a portion of their polypeptide chain. This proteolytic cut induces a conformational change that forms the functional active site. This mechanism prevents premature activity in the cell of origin.

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.