Biomolecules practice · Mixed difficulty

Option C (Hemiacetal) is correct because the cyclic form of glucose is formed by the reaction of an aldehyde group with an alcohol group within the same molecule, resulting in a hemiacetal.

Option C (16) is correct because glucose has 4 chiral carbons, leading to $2^4 = 16$ possible stereoisomers.

Option C (Fructose) is correct because fructose is a ketohexose, meaning it has six carbon atoms and a ketone functional group.

Option B (Natural silk) is correct because natural silk is a protein fiber.

Option D (${\mathrm{B}_{12}}$) is correct because the aqueous solution of Vitamin B12 is known to be dark pink in color.

Option D (Acid value) is correct because the acid value is defined as the number of milligrams of KOH required to neutralize 1 gram of fat or oil.

Option B (They do not taste sweet) is correct because polysaccharides are complex carbohydrates that are not sweet, unlike monosaccharides and disaccharides.

Option C ($\mathrm{Na}$ metal) is correct because sodium is the most abundant cation in extracellular fluid, playing a crucial role in maintaining water balance.

Option C (Polysaccharide) is correct because cellulose is a complex carbohydrate composed of many glucose units linked together, classifying it as a polysaccharide.

Option A (Biofuels to provide energy) is correct because carbohydrates are broken down into glucose, which is then used in respiration to produce energy.

Option B (increase the rate of a chemical reaction) is correct because enzymes are biological catalysts that speed up chemical reactions.

The correct answer is D (I, II, IV) because polysaccharides, nucleic acids, and proteins have molecular weights greater than 10000 daltons and are acid-insoluble, while lipids, although acid-insoluble, generally have lower molecular weights.

Option B (Proteins with specific structure) is correct because enzymes are biological catalysts made of proteins with specific three-dimensional structures that determine their function.

Option D (DNA has thymine and RNA has uracil) is correct because DNA contains the nitrogenous base thymine (T), while RNA contains uracil (U) instead of thymine.

Option D (All of these) is correct because gelatin, casein, and plasma protein are all examples of proteins.