MCQs

The fundamental function of an enzyme is to act as a biological catalyst, lowering the activation energy and speeding up a reaction while remaining unchanged at the end. Specificity is about substrate choice, sensitivity relates to environmental factors, and regulation refers to control of its activity.

Secondary structure refers to the regular, repeated local spatial conformations of the polypeptide backbone, stabilized by hydrogen bonds between backbone atoms. The primary structure is the sequence, tertiary is the overall 3D fold of one chain, and quaternary is multi-subunit assembly.

Triglycerides are composed of a single glycerol backbone esterified to three fatty acid chains. Saponification or enzymatic hydrolysis breaks these ester bonds, yielding the original components.

A peptide bond is a covalent bond formed via a dehydration reaction between the α-carboxyl group (-COOH) of one amino acid and the α-amino group (-NH2) of another, releasing a water molecule. R-groups are involved in tertiary structure interactions, not the primary backbone linkage.

The most fundamental structural difference is that DNA is a stable, double-stranded helix, whereas RNA is usually single-stranded. While sugar differences (deoxyribose vs. ribose) are also key, the overall strandedness is a major distinguishing feature. DNA contains thymine, RNA contains uracil.

Lipids are defined by their hydrophobic nature, being soluble in non-polar organic solvents (like ether, chloroform) but insoluble in water. This contrasts with carbohydrates and proteins which are generally hydrophilic.

The formation of a disaccharide involves the removal of a water molecule (dehydration synthesis) to form a glycosidic linkage between two monosaccharides. A peptide bond links amino acids, and an ester bond links fatty acids to glycerol.

Glucose and fructose both have the molecular formula C6H12O6. Glucose is an aldehyde sugar (aldose), while fructose is a ketone sugar (ketose). This difference in the carbonyl functional group makes them structural isomers, not identical molecules.

The term "carbohydrate" literally means hydrated carbon, reflecting the general ratio of one carbon to two hydrogens to one oxygen atom. Proteins contain nitrogen, and nucleic acids contain phosphorus, distinguishing them from this basic formula.

Carbohydrates, particularly monosaccharides like glucose, are the primary and immediate energy source broken down during cellular respiration. Proteins are mainly structural and catalytic, lipids are for long-term energy storage, and nucleic acids store genetic information.