Options (Choose One) - Biochemistry

Metabolism involves the complex network of chemical reactions in cells, categorized into anabolism (building molecules, requiring energy, $\Delta G > 0$) and catabolism (breaking down molecules, releasing energy, $\Delta G < 0$).

Amino acids are the building blocks of proteins and possess both an amino group ($-NH_2$) and a carboxyl group ($-COOH$). At specific $pH$, they exist as zwitterions: $H_3N^+-CHR-COO^-$.

The isoelectric point ($pI$) is the $pH$ at which an amino acid has a net charge of zero. At $pH < pI$, the amino acid is protonated and carries a positive charge; at $pH > pI$, it is deprotonated and carries a negative charge.

Proteins have four levels of structure: Primary (sequence of amino acids), Secondary ($\alpha$-helices and $\beta$-pleated sheets held by $H$-bonds), Tertiary (3D folding due to $R$-group interactions), and Quaternary (assembly of multiple polypeptide chains).

Enzymes function as biological catalysts by lowering the activation energy ($E_a$). Enzyme kinetics are often described by the Michaelis-Menten model, where $K_m$ represents the substrate concentration at which the reaction rate is $\frac{1}{2}V_{max}$.

Lipids include triglycerides, which are esters formed from glycerol and three fatty acids. The degree of unsaturation in a lipid can be determined using the Iodine Number, defined as the mass of $I_2$ in grams that reacts with $100\,g$ of the lipid.

Carbohydrates have the general empirical formula $C_x(H_2O)_y$. Monosaccharides like glucose ($C_6H_{12}O_6$) undergo condensation reactions to form disaccharides and polysaccharides, linked by glycosidic bonds.

Vitamins are micronutrients. Fat-soluble vitamins (e.g., Vitamin $A, D, E, K$) have long hydrocarbon chains or rings, while water-soluble vitamins (e.g., Vitamin $C$) have multiple $-OH$ groups allowing for hydrogen bonding with water.