MCQs

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.

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.

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.

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.

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.

The amino acid is covalently attached to the 3' acceptor stem of its cognate tRNA molecule. During elongation, the peptidyl transferase center of the ribosome catalyzes the nucleophilic attack of the amino group of the incoming aminoacyl-tRNA on the ester bond of the peptidyl-tRNA.

Adipose tissue, rich in triglycerides, serves as a padding that protects vital organs from physical shock. It also functions as a thermal insulator in subdermal layers, reducing heat loss from the body. Energy storage is its primary role, but the options highlight these secondary roles.

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%.

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.

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.

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.

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.