BIO NMDCAT

A nucleoside consists of a nitrogenous base plus a pentose sugar. A nucleotide is a nucleoside with one or more phosphate groups covalently bonded to the 5' carbon (or 3' carbon) of the sugar. The addition of phosphate is the defining difference.

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 alternating single and double bonds (conjugation) in carotenoids create a delocalized electron system that can absorb specific wavelengths of visible light. This makes them colored pigments (e.g., orange in carrots, red in tomatoes) that play roles in photosynthesis and photoprotection.

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.

Glycogen is more extensively branched than starch's amylopectin. Branching creates numerous terminal non-reducing ends. Glycogen phosphorylase can act on all these ends simultaneously, leading to a much faster release of glucose-1-phosphate to fuel the animal's high metabolic rate.

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.

Inorganic ions, like Mg²⁺, Zn²⁺, or Fe²⁺, that bind loosely to an enzyme and increase its activity are termed activators or inorganic cofactors. A coenzyme is an organic molecule. A prosthetic group is a tightly-bound organic or inorganic molecule.

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).

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.

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.