BIOLOGICAL MOLECULES

The cis-double bond introduces a fixed bend in the hydrocarbon tail. This prevents the fatty acid chains from packing closely together, increasing the free volume within the bilayer and thereby increasing its fluidity and permeability compared to saturated chains.

Aspirin (acetylsalicylic acid) acts by transferring its acetyl group to a serine hydroxyl in the active site of COX enzymes. This chemical modification is covalent and permanent (for the life of the enzyme), making it an irreversible inhibition, not a reversible binding interaction.

Some proteins can refold spontaneously into their native, biologically active conformation after the denaturing agent is gently removed. This is called renaturation. This ability indicates that the primary sequence remains intact and contains all the information for folding.

A glycosidic bond is the covalent linkage that joins monosaccharides into polysaccharides. A peptide bond is the analogous covalent linkage that joins amino acids into polypeptide chains. Both are formed by dehydration synthesis and create the primary polymer backbone.

The classification depends on the carbonyl group's position. If the carbonyl is at the end of the carbon chain (C1), it is an aldehyde group and the sugar is an aldose. If the carbonyl is on an inner carbon (C2 for the most common ketose, fructose), it is a ketone group and the sugar is a ketose.

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.

"Amphipathic" describes a molecule with both hydrophilic (water-loving, polar head group) and hydrophobic (water-fearing, non-polar fatty acid tails) parts. This dual property forces them into a bilayer arrangement where the heads face water and the tails are sequestered away from it.

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.

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.

Enzymes, like all catalysts, speed up the rate of a reaction by providing an alternative pathway with a lower activation energy (Ea). They do not change the overall free energy change (ΔG) or the equilibrium constant of the reaction. Without this rate enhancement, metabolic reactions would be too slow to sustain life.

A missense mutation is a single nucleotide change that results in a codon for a different amino acid. Here, arginine is replaced by alanine, which will likely alter the protein's primary structure and potentially its function. A silent mutation codes for the same amino acid.

According to Chargaff's rules, if C = 30%, then G = 30%. Total C+G = 60%. The remaining 40% is A+T, so A = 20% and T = 20%.

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.