SOME PROTEIN JOBS: MOLECULAR COUNTERPARTS TO OUR "REAL WORLD" MACHINERY, AND MORE Proteins make up the machinery of our cells, most working by converting energy in an ATP molecule into force. They use energy (delivered to them by ATP) to drive metabolic reactions, do mechanical work, such as moving muscles, rotating cilia and flagella, and transporting substances across membranes. Carbohydrates supply the energy to make ATP, nucleic acids the coded information and lipids play many roles, a particularly important one being membrane composition. This chart develops the idea of proteins as "machines", chains that are shaped to do specific jobs in the cells. Some jobs in a cell have counterparts in the tools and machinery used in the human world. (Some, of course, are quite different, but that's a story for another page...)
MACHINE	FUNCTION	EXAMPLE OF MOLECULAR TOOLS OR MACHINES	IMAGES OF WORKING PROTEINS
Structures Tracks , cables, filaments, beams, struts, cross-links, pipes	Transmit force; reinforce  Transmit tension, maintain shape	Microtubules made of tubulin,  collagen	Long hollow tubes http://www.rcsb.org/pdb/molecules/pdb4_2.html
Motors and Gears  Linear Motors	Moving things, Turn shafts, move along lines in step-wise fashion	Myosin grabs actin filaments and pulls. Dynein and kinesin crawls along microtubules. Kinesin goes out to membrane and dynein goes back.	Molecular "fingers" of stalk are able to grab hold of tubes. 1. http://www.stir.ac.uk/departments/naturalsciences/DBMS/ coursenotes/30CB/KINESINS1.html
Motors and Gears   Rotary Motors	Rotates cilia and flagella	Bacterial flagella protein	Protein dynein moves microtubules. http://www.bmb.leeds.ac.uk/illingworth/motor01/#dynein
Pumps	Move fluids and ions from one side of a membrane to another.	Membrane channel proteins, e.g.potassium-sodium pump	The protein pump (brown) is shaped to let one ion, sodium, go through.
Joiners,  hinges and clamps	Make compounds; Hold workpieces	Enzymes e.g., aldosase, an enzyme	Aldosase - NIH The active site of the enzyme aldosase joins two molecules, red and yellow here, together in a cradle so they can bond.
Chaperones	Assists movement, structures development, enzymatic action by shielding molecules from charges of other molecules.	Serpin, helps the triple helix collagen fold.(See above.)	Some scientists think the kind of "cradle" of red beta sheets helps the serpin hold onto the collagen strands.
Holders and Transporters	Carries molecules, usually with the help of a metal, to where they are needed.	Hemoglobin holds and transports oxygen to where it is needed.	Hemoglobin is made of 4 protein strands, each of which holds a heme (green), a kind of platter that carries the oxygen.
Cutters	Cut into pieces	Enzymes e.g. lysosyme	The active site of the enzyme lysosyme breaks a molecule into several pieces. www.sci.sdsu.edu

Decoders

Identify molecular fragments

The 'stalk" or barrel of an antibody holds on firmly while two "hands" identify specific molecules.