Biology Practice Test: Biomolecules

Proteins are long chains of amino acids joined by peptide bonds. Nucleotides build nucleic acids, and simple sugars build carbohydrates.

Every amino acid has an amino group, which contains nitrogen. Carbohydrates and fats are made only of carbon, hydrogen and oxygen.

Animals store glucose as glycogen, a highly branched polysaccharide. Starch is the storage form in plants, and cellulose builds plant cell walls.

Saturated fatty acids have straight chains with no double bonds, so they pack closely and stay solid. Double bonds in unsaturated fatty acids put kinks in the chains, which keeps oils liquid.

Each nucleotide has a five-carbon sugar, a phosphate group and a nitrogen base. The last option describes an amino acid, and the third describes a phospholipid.

Enzymes lower the energy needed to start a reaction, so it happens faster at body temperature. The enzyme is not used up and can be used again and again.

Each enzyme works best at a certain pH. Far from that pH, the bonds that hold the enzyme's shape change, the active site no longer fits the substrate, and activity stops.

Iodine turns blue-black when starch is present. Glucose is tested with Benedict's solution, and protein with biuret reagent.

Dehydration synthesis joins monomers and gives off water. Hydrolysis is the reverse: water is added to split a larger molecule apart.

The order of amino acids determines how a protein folds, and its folded shape determines how it works. Even one change can alter the shape and the function.