Construct and revise an explanation, based on evidence, for how carbon-based macromolecules (carbohydrates, lipids, proteins, and nucleic acids) are built from smaller subunits and carry out the functions of life (Louisiana Student Standards for Science, High School Biology, HS-LS1-6).

What this topic is asking

Louisiana's LS1 standards (HS-LS1-6) ask you to explain how the carbon-based macromolecules of life are built from smaller subunits and what they do. For LEAP 2025 Biology you should know the four classes (carbohydrates, lipids, proteins, nucleic acids), the monomer (subunit) of each, and the function each carries out. The test often gives a description of a molecule (its subunits or its job) and asks you to identify the class, which uses the structure-and-function crosscutting concept.

Carbohydrates: quick energy

Carbohydrates are the body's quick-energy source: glucose is broken down in cellular respiration to release energy fast. Plants store glucose as starch and use cellulose to build the cell wall, while animals store it as glycogen. When a question mentions a sugar or a fast energy source, the class is carbohydrate.

Lipids: energy storage, insulation, and membranes

So although both carbohydrates and lipids store energy, lipids pack more energy and are the long-term store, while carbohydrates are the quick store. The role of phospholipids in the membrane links this topic back to transport.

Proteins: the workhorses

Proteins are made of amino acids joined into chains that fold into a specific three-dimensional shape. There are 20 different amino acids, and the order in which they are joined (set by the DNA) determines the shape, and the shape determines the function. Proteins do an enormous range of jobs:

• Enzymes that speed up reactions.
• Structural molecules (such as those in muscle, skin, and hair).
• Transport proteins (in the membrane and in blood).

Because a protein's shape comes from its amino-acid sequence, anything that changes the sequence (a mutation) can change the shape and so the function, a link the test makes to genetics.

Nucleic acids: the genetic information

Nucleic acids are made of nucleotides (each a sugar, a phosphate, and a base). The two kinds are DNA, which stores the genetic instructions, and RNA, which helps carry those instructions out to build proteins. Nucleic acids are how information is stored and passed on, the foundation of the genetics module.

Try this

Q1. Name the monomer (subunit) of proteins and the monomer of nucleic acids. [2]

• Cue. Proteins are made of amino acids; nucleic acids are made of nucleotides.

Q2. State one function of carbohydrates and one function of proteins. [2]

• Cue. Carbohydrates: quick energy (or structure, such as cellulose). Proteins: enzymes (or structural molecules, or transport).