BIOLOGICAL MOLECULES

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.

The 20 common amino acids all share a common backbone (amino group, α-carbon, carboxyl group) but differ only in their side chain, the R-group. The size, shape, charge, hydrophobicity, and chemical reactivity of the R-group confer the unique properties to each amino acid.

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.

Lysozyme specifically targets the β-1,4 glycosidic bond between N-acetylmuramic acid and N-acetylglucosamine in the peptidoglycan layer of bacterial cell walls. This bond cleavage weakens the cell wall and causes bacterial lysis.

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.

Molecular chaperones are proteins that assist the non-covalent folding/unfolding and assembly/disassembly of other macromolecular structures. They provide a protected environment for a protein to fold correctly, thereby preventing improper interactions that lead to denaturation and aggregation.

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.

The sugar in RNA is ribose, which has a hydroxyl (-OH) group on the 2' carbon. The sugar in DNA is deoxyribose, which has only a hydrogen atom at the 2' carbon. This single oxygen difference makes RNA chemically more reactive and less stable than DNA.

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.

This is a classic example of feedback inhibition, a negative feedback loop. The final product binds to an allosteric site on enzyme 4 (often the first committed step enzyme), causing a conformational change that reduces its catalytic activity and shuts down the pathway.

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.

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.

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.

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.

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.

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.

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.

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.

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).