Grass and Potato
A cow lives on grass and a person cannot digest it, yet both digest potato. Grass fiber and potato starch are both made of nothing but glucose.
If the building block is the same, what makes one food and the other not?
Page 1
Science · Honors Biology
Chapter 1: Biochemistry
Same elements, different arrangement, different job.
A cow lives on grass and a person cannot digest it, yet both digest potato. Grass fiber and potato starch are both made of nothing but glucose.
If the building block is the same, what makes one food and the other not?
Make your guess to turn the page.
Still to come: 11 pages · Lab · Words to Know · What We Learned · 4 questions · Explain It in Writing · Open Questions
The idea this lesson is working on — Students assume that two molecules behaving so differently must be made of different things. The book shows acid giving pure glucose from both, and the lab shows a glucose chain has only one possible sequence, so sequence cannot be the answer. Ask: if the parts and their order are the same, what is left to differ? The idea to reach is bond geometry, alpha against beta.
Same elements, different arrangement — Methylation analysis (Haworth and others) established the 1→4 links, and X-ray work on cellulose in the late 1920s gave the 1.03 nm cellobiose repeat. Rundle and colleagues in the 1940s showed amylose–iodine as a six-residue helix. Lipids carry far less oxygen relative to carbon, which is why they store about twice the energy per gram, and they are stored without the water that glycogen binds.
Gorter and Grendel’s lucky answer — Their 1925 paper reported lipid-to-surface ratios near 2 for several species. Later work found acetone extraction had recovered too little lipid and the dried-cell surface area had been underestimated; the errors roughly offset. The bilayer conclusion survived, and membrane proteins were added to it in the fluid mosaic model of 1972.