Week 3 — Biological Macromolecules

Why this matters

A nursing student learning about sickle cell disease and a home cook watching an egg white set both meet the same four kinds of large molecules.

In plain language

Every living thing is built from a few kinds of very large molecules, and this week you meet all four of them. You will learn how cells snap small pieces together into long chains, and how they take those chains apart again with water. You will meet carbohydrates (sugars and chains of sugars, such as starch) and lipids (fats, oils, and their relatives, which avoid water). You will also meet proteins (chains of amino acids that fold into working shapes) and nucleic acids (DNA and RNA, which store a cell's instructions). Most of all, you will see the idea that runs through this whole course: structure determines function (a molecule's shape decides the job it can do).

• Already covered: Week 1 set up how biologists test a claim with a controlled experiment; Week 2 covered atoms, bonds, water, and pH.
• This week: the four classes of large biological molecules, how they are built and broken, and the rule that structure determines function.
• How they connect: these molecules are built from the atoms and bonds of Week 2, they are assembled and digested in water, and you test them with a control group exactly as Week 1 taught.
• Where we're going next: Week 4, Cell Structure & Function, puts these molecules to work inside the cell, starting with the membrane that phospholipids build.

Focus

How are life's big molecules built, and how does shape decide their job?

By the end of this module, you should be able to:

• [ ] count the bonds and water molecules when a chain is built or broken
• [ ] sort a molecule into one of the four classes by its building block
• [ ] explain why lipids are not polymers and order the four protein levels
• [ ] read an iodine starch test and explain each color from shape

To-do

Plan your week

1. Read Chapter 3 (about 40 minutes), then the lecture and slides.
2. Work the lecture tutorial (60–90 minutes) and the practice set (about 20 minutes).
3. Run the Biology Lab & Inquiry (about 2 hours), then the discussion and the assignment.
4. Take the quiz.

This week's checkpoint: explain why sugar water stays amber in the iodine test even though sugar is a carbohydrate.

You've got this

Take it in order; ask your instructor if a step snags.

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