Biocurious is a weblog about biology, quantified.

Molecule of the Month: Fatty Acid Synthase

by PhilipJ on 1 June 2007

Fat, these days, is a bad word. But we can’t survive without fats, and more particularly, without fatty acids. Fatty acids are small molecules composed of a long string of carbon and hydrogen atoms, with an acidic group at one end. They are used for two essential things in your body. First, they are used to build the lipids that make up all of the membranes around and inside your cells. Second, fatty acids are a concentrated source of energy, so they are often connected to glycerol to form fats, which are a compact way to store energy until it is needed. But as we all know, if we eat too much, this extra fat can build up!

We get most of our fatty acids from our diet, but our cells also make enzymes that can construct most of our fatty acids, if needed. The construction of fatty acids is a stepwise process, adding carbon atoms two at a time to the growing chain. It takes four separate chemical reactions at each step, first adding the carbon atoms and then reducing them to the proper hydrocarbon form. It also takes several additional enzymes to start the process, and a few more to clip off the finished fatty acid at the end.

Remarkably, in our cells all of these complicated tasks are performed by one long protein chain. It folds into a bunch of connected domains that each do different steps in the reaction. You can see a low resolution structure of our complicated fatty acid synthase in the PDB file 2cf2. The one shown here is from a fungus, from PDB entries 2uvb and 2uvc, which combines all of these functions in two chains. The entire complex has 12 chains total, six alpha chains the middle (in green here) and three beta chains at each end (in blue). All the action happens inside this big hollow ball. Inside, the growing fatty acid is attached to a flexible tether and it flips from site to site inside the enzyme as more and more carbon atoms are added.

More from David Goodsell here.



  1. A viewer    3790 days ago    #

    Does David sanction your posting his work here as a direct copy from pdb.org without acknowledging where your cut-n-paste job is coming from? If you like molecule of the month send people there, don’t rip it off to drive up your web hits.


  2. PhilipJ    3790 days ago    #

    Thanks for bothering to read an entire post and noticing that I always make a point of mentioning David by name and linking to his personal website!

    Oh, wait.


  3. Andre    3790 days ago    #

    Just to clarify further, the header image is also David Goodsell’s, as described prominently on our about page, and is used with his permission.


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