Four case studies
Each has a working model to explore, the evidence in four parts, a methodology and limitations note, and space for your own conclusions.
Protein folding and sequence space
A protein is a chain of amino acids that, for most enzymes, must fold into one particular shape to work. Two different 'searches' are often confused here: the physical search a chain makes for its folded shape, and the historical search for a sequence that folds at all.
Open →The bacterial flagellum
A rotary motor in the cell envelope of many bacteria, driven by ion flow, that turns a long helical propeller. It is the best-known example in the irreducible-complexity debate, and also one of the best-studied machines in biology.
Open →Genetic information and mutation
DNA stores the sequence of every protein in three-letter codons. Changing a single letter can do nothing, change one amino acid, or stop the protein short. What mutations do, and how often each kind happens, is measurable.
Open →Molecular machinery: ATP synthase and kinesin
ATP synthase makes most of a cell's ATP by turning. A flow of protons spins a ring in the membrane, and the rotation squeezes ADP and phosphate together in three catalytic sites. Kinesin walks cargo along microtubules, one ATP per 8-nanometre step.
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