Carbohydrates: These macromolecules include sugars and their polymers (polysaccharides). Sugars provide energy and is a carbon source so when sugars from glycosidic linkages to make a polymer, that polymer also provides and stores energy. Also, depending on the configuration of the sugars, polysaccharides play different structural roles. For example, cellulose is a main component of plant cell walls, and chitin makes up the exoskeleton of arthropods and fungi cell walls.
Lipids: These macromolecules have hydrophobic behaviors and include fats, phospholipids, and steroids. Fats are made up of fatty acids, which consists of a long hydrocarbon tail and a carboxyl group as the head. This structure make fats good energy storage molecules and they can storage twice the energy than carbohydrates can. Phospholipids is a glycerol joined to fatty acids and a negatively charged phosphate group. Because of their unique structure, phospholipids make up the cell membranes to form a boundary between the internal parts of the cell and the cell's environment. Steroids have four connected carbon rings that are joined to different functional groups. Again, because of this structure, some steroids, like cholesterol, is part of animal cell membranes and precursor for some hormones.
Proteins: These macromolecules are one or more polypeptide chains that are folded into a specific three-dimensional shape. Polypeptides are polymers of amino acids, which is made of a asymmetric carbon bonded to a hydrogen, an amino group, a carboxyl group, and a variable/R group. The R group determines the properties of the amino acid. Although there are only 20 animo acids, they can bond in so many different ways that it results in many polypeptides, which makes a large variety of proteins. Because the order amino acids in a protein make a unique genetic code, proteins have the instructions for almost every process of life. This includes their function as enzymes to speed up and catalyze reactions, transporting materials, receiving and processing stimuli, directing movements, etc.
Nucleic Acids: These macromolecules carry a genetic code and transfers the hereditary information. Deoxyribonucleic acid (DNA), which has the shape of a double helix, can unravel and replicate itself because of its base-pairing property. For nucleotides in DNA, monomers of nucleic acids, adenine always pairs with thymine and guanine always pairs with cytosine. In this way, genes are passed down through the generations. Ribonucleic acid (RNA) are able to direct protein synthesis because of the its structure: Again, because of the base-pairing property, DNA transfers the genetic code to RNA during transcription and mRNA (messenger RNA) carries the code to ribosomes to synthesize proteins. (For RNA, adenine always pairs with uracil and guanine still always pairs with cytosine.)
