Your textbook describes how the primary structure (a sequence of amino acids determined by the genetic code) is folded into a twisted and pleated secondary structure, then folded again into a complex tertiary structure. Sometimes, tertiary proteins are combined to form quaternary proteins. Sort of like origami, but way more useful. And way tinier.
I'd like to mention a interesting phenomenon related to protein folding and "citizen science" using an online game called Foldit.
The Foldit game is an online puzzle game in which anybody can try their hand and finding which way a given protein folds most efficiently. Interestingly, this has proven to yield useful results for biochemists not obtainable by traditional methods.
If you like video games . . . and the idea of actually contributing to scientific knowledge intrigues you . . . why not try your hand at Foldit?
Want to know more?
Online Gamers Achieve First Crowd-Sourced Redesign of Protein
Jessica Marshall & Nature magazine
Scientific American Online January 22, 2012
[Brief article about recent redesign of a protein by online gamers using Foldit. Original paper published in Nature Biotechnology]
Foldit Online Protein Puzzle
Scientific American Citizen Science accessed 23 January 2012
[Brief description of the online game Foldit and the goals of the project.]
Foldit - Solve Puzzles for Science
[Direct link to portal for the game Foldit]