Construct an explanation that the essential functions of life are carried out by the four macromolecules (carbohydrates, lipids, proteins, and nucleic acids) built from monomers (Tennessee Academic Standards for Science, Biology I, BIO1.LS1).

What this topic is asking

The Tennessee LS1 standards ask you to explain that the essential functions of life are carried out by large biological molecules, the macromolecules, and that these are polymers built from smaller monomers. For the Biology I EOC you need the four macromolecules, the monomer that each is built from, the function of each, and especially why a protein's shape (set by its amino-acid sequence) determines what it can do. Items frequently give a monomer or a function and ask you to name the macromolecule.

The monomer-and-polymer idea

This pattern organizes all four groups, so the single most useful thing to memorize is the monomer of each macromolecule. Once you know the monomer, the EOC item is usually asking you to match it to a function.

Carbohydrates: quick energy and structure

Carbohydrates are made of monosaccharides (simple sugars), the most important being glucose. They are the body's main source of quick, usable energy, broken down in cellular respiration to release ATP. Carbohydrates also serve structural roles: plants link glucose into cellulose for their cell walls, and animals store glucose as glycogen. The elements are carbon, hydrogen, and oxygen, usually in a ratio that gives the name "carbo-hydrate."

Lipids: long-term storage and membranes

Lipids (fats, oils, and waxes) are built from fatty acids and glycerol and are nonpolar, so they do not dissolve in water. Their functions are long-term energy storage (fats store more than twice the energy per gram of carbohydrates), forming the phospholipid bilayer of cell membranes, insulation, and acting as some hormones (such as steroid hormones). When the EOC describes a molecule that is nonpolar, makes up membranes, or stores energy long-term, it is pointing to a lipid.

Proteins: the workhorses

This shape-determines-function idea is the heart of the standard and connects directly to mutations and protein synthesis. An enzyme works because its shape fits its substrate; change the shape and it no longer fits.

Nucleic acids: the information molecules

Nucleic acids are built from nucleotides, and they store and carry genetic information. There are two: DNA, the long-term store of the cell's instructions, and RNA, which carries those instructions to build proteins. Each nucleotide has a sugar, a phosphate, and one of several nitrogen bases; the order of bases is the genetic code. This is the link to the LS3 heredity standards, where DNA and protein synthesis are developed in full.

Try this

Q1. Match each macromolecule to its monomer: carbohydrate, protein, nucleic acid. [3]

• Cue. Carbohydrate to monosaccharide (simple sugar); protein to amino acid; nucleic acid to nucleotide.

Q2. Explain why proteins can carry out so many different functions in a cell. [2]

• Cue. Proteins are built from 20 different amino acids in any order, and the order determines the folded shape; the huge number of possible shapes lets proteins do many different jobs, because shape determines function.