Unit 2: The Chemistry of the Four Macromolecule Classes
Carbohydrates, lipids, proteins, and nucleic acids as four different answers to the same two chemical moves.
6 topics · 21 questions
Each topic is a path, not a menu: work down it in order and every question builds on the one above. Click any of them to watch the answer draw itself.
Building Polymers by Condensation and Hydrolysis
- How it worksHow does removing one water molecule link two monomers together into a growing polymer?
- Common mistakeWhy isn't hydrolyzing a polymer just the reverse of burning it?
- Going furtherWhat happens to a polymer's building-block chemistry when a cell needs to break it back down for energy?
Your turn1 of 2
A cell builds a polymer by linking 22 monomers together through condensation reactions, one water molecule released at each new bond. Find how many water molecules are released in total.Carbohydrate Structure and Glycosidic Bonds
- How it worksHow does a glycosidic bond link two sugar rings together at the anomeric carbon?
- Worked exampleFind how many water molecules are released when five glucose monomers link into one straight-chain polysaccharide.
- Common mistakeWhy isn't starch and cellulose being built from the same sugar the reason your body can digest one but not the other?
- Going furtherWhat happens to a polysaccharide's overall shape when its glycosidic bonds all point the same direction instead of alternating?
Your turn1 of 2
Find how many water molecules are released when 29 glucose monomers link into one straight-chain polysaccharide.Lipid Structure: Fatty Acids and Triglycerides
- How it worksHow does a kink from a carbon-carbon double bond in a fatty acid's tail stop it from packing tightly against its neighbors?
- Going furtherWhat happens to a fat's melting point as you add more carbon-carbon double bonds to its fatty acid tails?
- Common mistakeWhy isn't 'saturated' a word about how much fat a food contains?
Your turn1 of 2
A nutrition label calls a snack food 'high in saturated fat,' and a student interprets this as meaning the food simply contains a large total amount of fat. A friend points out this reading is wrong. What does 'saturated' actually describe?Amino Acid Structure and Side-Chain Chemistry
- How it worksHow does the central carbon of an amino acid hold four different groups that give each amino acid its own chemistry?
- How it worksWalk me through how an amino acid's side chain can be charged, polar, or oily while its backbone chemistry stays identical every time.
- Common mistakeWhy isn't an amino acid's side chain just decoration that doesn't affect the protein's chemistry?
- Going furtherWhat happens to an amino acid side chain's charge as the surrounding pH crosses its pKa?
Your turn1 of 2
An amino acid's acidic side chain has a pKa of 5.59. Find the percent of that side chain sitting in its deprotonated, negatively charged form at a surrounding pH of 8.The Peptide Bond and Its Partial Double-Bond Character
- How it worksHow does electron sharing between the peptide bond's carbon and nitrogen give it partial double-bond character?
- Common mistakeWhy isn't the peptide bond just an ordinary single bond like the one holding a side chain to the backbone?
- Going furtherWhat happens to a chain of amino acids' possible shapes once every peptide bond in it is locked flat?
Your turn1 of 2
A student expects the bond linking two amino acids to rotate as freely as the bond linking a side chain to the backbone, since both look like single bonds when drawn in a simple structural diagram. In reality the peptide bond barely rotates at all. What makes it behave differently from an ordinary single bond?Nucleotide Structure and the Chemistry of Nucleic Acids
- How it worksHow does a phosphodiester bond link one nucleotide's sugar to the next nucleotide's phosphate?
- How it worksWalk me through how the negative charges on a nucleic acid's phosphate backbone end up on the outside, away from the bases.
- Common mistakeWhy isn't RNA just DNA with a different sugar as far as its chemistry goes?
- Going furtherWhat happens to a nucleotide's role when it gets used as an energy carrier instead of a DNA building block?
Your turn1 of 2
A student notices that RNA and DNA are both built from a sugar, a phosphate, and a base, and concludes RNA must be chemically identical to DNA except for swapping in a different sugar. Why is this an oversimplification?