Science · Biology
Chapter 1: The Nature of Life
Four families, one assembly reaction.
In 1955 Frederick Sanger finished the first complete sequence of a protein: insulin, 51 amino acids in two chains. Hemoglobin, keratin and the enzyme amylase use the same twenty kinds of amino acid, yet one carries oxygen, one builds hair and one digests starch.
How can the same twenty building blocks make molecules with such different jobs?
Make your guess to turn the page.
Still to come: 9 pages · Lab · Words to Know · What We Learned · 4 questions · Explain It in Writing · Open Questions
The idea this lesson is working on — Students file the four macromolecule families as four unrelated lists. The book states one assembly model, condensation with n − 1 waters and kⁿ sequences, and the lab holds chain length fixed across families so the shared reaction and the different variety show side by side. Ask: what is the same for every polymer, and what is different? The idea to reach is one chemistry, with monomer variety deciding versatility.
Four families, one assembly reaction — Carbohydrates, proteins and nucleic acids are polymers built by removing water between monomers and broken by adding it back. Triglycerides are not polymers but form by the same kind of condensation (ester bonds). The kⁿ count assumes a linear chain with one kind of link; glycosidic links (alpha and beta, 1-4 and 1-6) add variety to carbohydrates. Ribozymes, including the ribosome’s catalytic core, show that RNA can catalyze.
Function follows from shape — A protein’s job depends on the three-dimensional shape its amino acid sequence folds into. Change the sequence, change the shape, lose the function, which is what most harmful mutations do. Sickle cell hemoglobin carries a single substitution, glutamic acid to valine at position 6 of the beta chain.