Practice Questions

Cellulose is a linear homopolymer of glucose linked by β-1,4-glycosidic bonds, forming strong microfibrils that are embedded in the plant cell wall matrix. Its primary role is to provide rigidity and structural support to plant cells.

Disulfide bridges (-S-S-) are covalent cross-links formed between cysteine R-groups. They lock the tertiary structure in place. Reducing agents like β-mercaptoethanol break these linkages, which can drastically destabilize the protein's 3D fold, causing unfolding. Detergents and urea primarily disrupt non-covalent interactions.

By binding separate substrates in adjacent binding sites on a single enzyme surface, the enzyme converts a slow, intermolecular, second-order reaction into a much faster, intramolecular, first-order reaction. This drastically increases the probability of productive collisions.

The Anfinsen experiment with ribonuclease showed that the amino acid sequence contains all the information needed for the protein to fold into its correct tertiary structure. Upon removal of a denaturant, the protein refolded spontaneously, proving structure is sequence-determined.

Hydrogenation adds hydrogen atoms across the carbon-carbon double bonds in unsaturated oils, converting them to saturated single bonds. This straightens the fatty acid chains, allowing them to pack more tightly and solidify at room temperature.

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.

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.

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.

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.

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.