Relate the structure of the four major biological macromolecules to their functions in living organisms (North Carolina Standard Course of Study, Biology, LS.Bio.1).

What this topic is asking

North Carolina LS.Bio.1 asks you to relate the structure of the four major macromolecules to their functions. For the Biology EOC you need to know the four groups (carbohydrates, lipids, proteins, nucleic acids), the monomer that builds each, what each does, and how to identify them from a clue. The crosscutting concept is structure and function: a molecule's building blocks and shape determine the job it can do.

Carbohydrates: quick energy

Carbohydrates are the body's quick energy source: glucose is broken down in cellular respiration to release energy. Single sugars (monosaccharides like glucose) join into chains: starch stores energy in plants, glycogen stores energy in animals, and cellulose is the tough structural carbohydrate in plant cell walls. A clue that points to a carbohydrate is the word "sugar" or "starch," or a chemical made only of carbon, hydrogen, and oxygen in that simple ratio.

Lipids: long-term storage and membranes

Lipids are fats, oils, waxes, and steroids. They are built mainly from glycerol and fatty acids and are hydrophobic (they do not mix with water). Their functions are long-term energy storage (more energy per gram than carbohydrate), insulation and protection, and forming the phospholipid bilayer of every cell membrane. Some hormones (such as steroid hormones) are lipids. A clue that points to a lipid is "fat," "oil," "membrane," or the building blocks "glycerol and fatty acids."

Proteins: the versatile workhorses

Because shape is everything, anything that changes a protein's shape changes its function. Heat or extreme pH can denature a protein, unfolding it so it no longer works, which is why high fevers and the wrong pH are dangerous to enzymes. The link from gene to protein to trait runs through this molecule, so proteins connect this topic to genetics.

Nucleic acids: the information molecules

Nucleic acids are polymers of nucleotides (a sugar, a phosphate, and a nitrogen base). The two kinds are DNA, which stores the genetic instructions, and RNA, which helps build proteins from those instructions. Nucleic acids carry information, not energy or structure, and they are the basis of heredity. A clue that points to a nucleic acid is "DNA," "RNA," "genetic," or the building block "nucleotide."

Try this

Q1. Name the monomer of each of the four macromolecules. [4]

• Cue. Carbohydrate, monosaccharide (sugar); lipid, glycerol and fatty acids; protein, amino acid; nucleic acid, nucleotide.

Q2. Explain why a protein stops working when it is heated strongly. [2]

• Cue. Heat denatures the protein, changing its three-dimensional shape; because function depends on shape, the protein can no longer do its job.