Water is a very polar substance that will not interact well with nonpolar macromolecules. Enzymes (proteins), oligosaccharides (carbohydrates), and nucleic acids all contain polar regions that make them soluble in aqueous environments. Lipids, however, are hydrocarbons and generally lack a polar region. Lipids would not be soluble in water, but would be soluble in nonpolar organic solvents, like chloroform. We can conclude that cholesterol is a lipid.

ATP stands for adenosine triphosphate and GTP stands for guanosine triphosphate. Both of them are nucleic acids, meaning that they must contain a pentose sugar, a nitrogenous base, and phosphate groups. Both ATP and GTP contain three phosphate groups. The only difference between ATP and GTP is their nitrogenous base. ATP contains adenine whereas GTP contains guanine. Recall that adenine and guanine are both purines.

ATP and GTP do not contain any pyrimidines (cytosine, thymine, and uracil).

Amphipathic molecules have both a polar and nonpolar region. This amphipathic quality allows phospholipids to create the plasma membrane in eukaryotic cells. The polar region is the phosphate head, which interacts with the aqueous cytosol and extracellular environment. The nonpolar region is the fatty acid tail, which is sequestered in the bilayer of the membrane and helps reduce the permeability to certain molecules.

A phospholipid has a hydrophobic tail and a hydrophillic head. The hydrocarbon section composes the hydrophobic tail and dislikes water. The phosphate group composes of the hydrophillic head and likes water. The combination makes a semi-permeable membrane that we know as the lipid bilayer.

Macromolecules, such as proteins, nucleic acids, and polysaccharides, are composed of monomers. Each polymer is made from at least two smaller monomers. Protein monomers are amino acids, nucleic acid monomers are nucleotides, and polysaccharide monomers are monosaccharides. In order to form polymers, the monomers must form covalent bonds with one another.

For proteins, these covalent bonds are peptide bonds, and for saccharides they are glycosidic linkages.

Nucleotides are the monomers that make up nucleic acids. They are composed of a five-carbon sugar, a nitrogenous base, and a phosphate group. In building the polymer nucleic acid chain, the sugar and phosphate of one nucleotide align with those of another to build the phosphate-sugar backbone, while the nitrogenous bases will form hydrogen bonds across the helix to link two chains of nucleotides together. Phosphate groups carry negative charge; this gives the cell nucleus an overall negative charge and can be used to generate electrochemical gradients across the nuclear membrane.

Carboxylic acids are found in amino acids, and are not present in nucleic acids.

Chargaff found that in double-stranded DNA, the number of guanine bases should be equal to the number of cytosine bases, and the number of adenine bases should equal the number of thymine bases. These rules proved to be important pieces of evidence for the idea of complementarity, the theory that each DNA base pairs only with a specific other base on its opposite strand.

According to Chargaff's rules, the statement regarding guanine and cytosine bases is correct. The two other statements that are similarly worded are not correct because they do not compare the frequencies of two bases that are complementary to each other (adenine will not bind cytosine and guanine will not bind thymine). Finally, guanine-cytosine bonds are more stable than adenine-thymine bonds.

The backbone of DNA is made up of deoxyribose sugars linked to phosphate groups. These units are joined by phosphodiester bonds into chains. Nitrogenous bases are bound to the sugars of these groups and join DNA strands together by hydrogen bonds with their complementary base pairs.

Amino acids are the building blocks of proteins, and are not found in DNA. Alpha-linked glucose residues describe a type of polysaccharide, namely glycogen. Glycerol and fatty acids describe a type of lipid known as a triglyceride. Triglycerides and glycogen are primarily used in energy storage.

Peptide bonds form between the amine group of one amino acid and the carboxylic acid of another via a covalent linkage. The formation of a polypeptide chain from amino acid residues constitutes the protein primary structure.

Secondary structure is formed by hydrogen bonding between the amino and carboxyl backbone units of the polypeptide. Tertiary structure is formed by disulfide covalent bonds, hydrophobic interactions, and R-group hydrogen bonding. Quaternary structure is the joining of multiple polypeptide subunits.

Lipids are composed of hydrocarbon chains and are very nonpolar. Polar solvents interact well with polar solutes, but do not solvate nonpolar solutes. When lipids are placed in a polar solvent, they will group together to minimize surface contact with the solvent. These droplets of lipids, or micelles, act like containers for the lipid, keeping them grouped together instead of being distributed through the solvent.

The lipids do not precipitate as they are not necessarily in a solid form. Even lipids in the liquid state can form micelles.