Describe the four classes of biological macromolecules (carbohydrates, lipids, proteins, and nucleic acids), their monomers, and their roles in maintaining life processes (Virginia 2018 Biology SOL BIO.2.b).

What this topic is asking

Virginia Biology SOL standard BIO.2.b asks you to know the four classes of macromolecules that maintain life: carbohydrates, lipids, proteins, and nucleic acids. The Biology EOC expects you to match each one to its monomer (building block) and its function, and to understand that cells build these large molecules by joining monomers and break them down by adding water. This topic underpins enzymes, membranes, energy, and genetics, so it is foundational across the whole exam.

The four macromolecules

The exam wants you to know, for each class, the monomer and the main function. A simple table in your head, macromolecule, monomer, function, answers most items quickly.

Carbohydrates

Carbohydrates are made of carbon, hydrogen, and oxygen, with monomers called monosaccharides (simple sugars such as glucose). Two monosaccharides form a disaccharide (such as sucrose), and many form a polysaccharide. Their main role is energy: glucose is the fuel for cellular respiration. Carbohydrates also provide structure, for example cellulose in plant cell walls and starch as the plant's energy store. Carbohydrates are the body's fastest and most readily used energy source.

Lipids

Lipids include fats, oils, waxes, and steroids. They are built from glycerol and fatty acids and are nonpolar, so they do not dissolve in water. Their roles are long-term energy storage (they store more energy per gram than carbohydrates), forming the phospholipid bilayer of cell membranes, insulation and cushioning, and acting as some hormones (such as steroid hormones). The nonpolar nature of lipids is exactly why the cell membrane can form a barrier in the watery cell.

Proteins

Proteins do more different jobs than any other macromolecule: they act as enzymes (speeding up reactions), structural materials (muscle, hair, collagen), transport molecules (hemoglobin carrying oxygen), antibodies (defense), and hormones (such as insulin). The link between structure and function, sequence determines shape determines job, is one of the most tested ideas in biology.

Nucleic acids

Nucleic acids are DNA and RNA, polymers of nucleotides. Each nucleotide has a phosphate, a sugar, and a nitrogenous base. Their role is to store and carry genetic information: DNA stores the instructions, and RNA carries them to be made into proteins. Nucleic acids link this module to genetics (see DNA structure and replication).

Building and breaking macromolecules

Cells assemble polymers from monomers by dehydration synthesis (also called condensation): a molecule of water is removed as each new bond forms. They break polymers back into monomers by hydrolysis: a molecule of water is added to split each bond. Digestion is hydrolysis, breaking large food molecules into absorbable monomers. The two processes are opposites and are easy to remember as "remove water to build, add water to break."

Try this

Q1. Match each monomer to its macromolecule: amino acid, monosaccharide, nucleotide. [3]

• Cue. Amino acid to protein; monosaccharide to carbohydrate; nucleotide to nucleic acid.

Q2. Explain why a change in the amino acid sequence of a protein can stop it working. [2]

• Cue. The sequence determines how the protein folds, and the folded shape determines its function; a changed sequence can change the shape so it can no longer do its job.