You back up another pathway and you make sugar. You go in another direction, you make fats, but it all comes from this central core. Professor Morowitz argues that the Chart of Intermediary Metabolism is to biology what the periodic chart of elements is to chemistry. Morowitz, a biophysicist and author of some 17 books and nearly 150 articles, is a modest, congenial man with wide ranging interests. Moreover, his books have drawn praise from a broad and varied readership.
Autotrophs make all their own compounds starting with carbon dioxide, ammonia, and water.
I contend that the earliest organisms had the entire chart. People don't have the entire chart because they eat things that have those intermediate chemicals necessary for life. Autotrophs have the entire chemistry, and some are microorganisms that can carry out all the reactions. My guess is that the original ancestor was this kind of cell. It could make every carbon compound that you need for life starting with CO2.