Practice Questions

The glycosidic bond in sucrose is formed between the anomeric carbon (C1) of glucose and the anomeric carbon (C2) of fructose. Since neither carbonyl group is free to open into an aldehyde or ketone form, sucrose cannot reduce Cu²⁺ and is thus a non-reducing sugar.

A competitive inhibitor competes for the active site, effectively making it harder for the enzyme to bind its substrate. More substrate is required to reach half the maximum velocity. Therefore, the apparent Km (substrate concentration at 1/2 Vmax) is increased in the presence of a competitive inhibitor.

Amylose is a linear polymer of glucose with α-1,4 linkages. Amylopectin is a much larger, branched polymer that has both α-1,4 linkages in the straight chain and α-1,6 glycosidic bonds at the branch points approximately every 24-30 glucose units.

Kinases are a class of transferase enzymes that catalyze the transfer of a γ-phosphate group from a high-energy donor molecule like ATP to a specific substrate. Protein kinases phosphorylate specific serine, threonine, or tyrosine residues on target enzymes, regulating their activity. Phosphatases reverse this.

The amino-terminal ends of both the light (VL) and heavy (VH) chains form the antigen-binding site. These variable domains have highly diverse amino acid sequences from one antibody clone to another, creating a unique 3D surface that is specific for a single epitope.

The definition of competitive inhibition is a "competition" for the active site. At a high enough concentration, the substrate out-competes the inhibitor for the active site, so all enzyme molecules can still bind substrate and reach Vmax. The apparent Km is increased, but Vmax is ultimately unchanged.

Allosteric regulation is mediated by modulator molecules that bind to a site (allosteric site) physically distinct from the active site. This binding causes a conformational change that can either increase (allosteric activator) or decrease (allosteric inhibitor) the activity of the enzyme at its active site.

In covalent catalysis, a powerful nucleophilic R-group in the active site (e.g., the -SH of cysteine or -OH of serine) forms a transient covalent bond with the substrate. This acyl-enzyme intermediate is then resolved by another step, releasing the product and regenerating the free enzyme.

Specificity is the ability of an enzyme to choose exactly one substrate from a pool of similar molecules. This is due to the exact complementary fit and specific chemical interactions (ionic, H-bonding, hydrophobic) between the substrate and the R-groups lining the active site.

The nitrogenous bases in double-stranded DNA are stacked and have a lower absorbance. When the double helix is denatured into two random, single-stranded coils, the bases become unstacked. This unstacking increases their absorbance of UV light at 260 nm, a phenomenon known as the hyperchromic effect.