Plant Enzymes Vs. Animal Enzymes

Enzymes are proteins that catalyze or speed up chemical reactions. Most of the important chemical reactions in plants, animals and other organisms are enzyme-catalyzed reactions. Understanding how enzymes work is an important field of study in biochemistry.

There are thousands of different enzymes, each of which performs specific functions. Like all proteins, enzymes are composed of a chain of amino acids; the sequence of these amino acids determines how the enzyme folds up to adopt a particular 3-D structure. An enzyme's structure determines what it will bind to and how it will work. The sequence of the base pairs in the gene that codes for a given enzyme determines the amino acid sequence -- and thus the structure and function of the enzyme.

Plants and animals perform some similar functions -- replicating their DNA and breaking down sugars for energy, for example -- but they also perform many different functions. Consequently, animal and plant cells have some enzymes that are similar and some that are very different. Animals, for instance, don't carry out photosynthesis, so they don't need enzymes like ribulose-1,5 biphosphate carboxylase oxygenase (Rubisco), while plants don't have nerves, so they don't need enzymes like acetylcholinesterase.

Differences in plant enzymes and animal enzymes result from differences in their genomes. Since plants and animals need to perform both similar and different functions, plants and animals share some genes that are similar but have many other genes that are very different. The striking differences between plants and animals stem over a billion years of evolution. Like all life on earth, animals and plants share a common ancestor, but the relationship is very distant; according to "Biology," plants and animals last shared a common ancestor over a billion years ago.