Part 2. What is an enzyme?  (Pictured as the large “blob” in the preceding video)

Chemical analysis proves each kind of enzyme to be specific kind of protein molecule. 

What is the nature of a protein molecule? Chemical analysis has proven that each protein is a long chain of amino acids. There are many kinds of amino acids but they have a particular similarity. The molecular structures of the 20 kinds found to in proteins are shown in the following link. Challenge students to find the common features of each.

http://www.chem4kids.com/files/bio_aminoacid2.html

A. Note on the left side each diagram: Each amino acid has an amino group (NH₃⁺) and an acid group (COO^–) bonded through a central carbon atom. Then, attached to this central carbon is a unique side group. (Kids should not have to give attention to these side groups.)

B. To make the chain of amino acids, the amino group of one is bonded (via an enzyme and a “kick of energy”) to the acid group of the next as described in the following video. (Watch only the first 2 minutes; the rest is superfluous technical details.)

https://www.khanacademy.org/science/biology/macromolecules/proteins-and-amino-acids/v/peptide-bond-formation

C. Any number and kinds of amino acids can be linked one after another in this manner. The result is a   …-N-C-C-N-C-C-… chain with the side group of each amino acid hanging off to the side.

D. As the chain of amino acids exceeds 50 or so, it is called a protein. Some proteins, including enzymes, are 100s of units long.

E. The most important point is this. Each different protein (enzyme) has a specific lineup of which kind of amino acid is present at each position in the chain. The importance of this is: see F 

F.  Each side group has a particular chemical reactivity: hydrophilic/hydrophobic (attracting/repelling water), acid/base, etc. This reactivity among side groups results in the chain folding itself into a very specific configuration where certain side groups form the active site(s) to attract and hold the particular  reactant(s), catalyze the specific reaction, and release the product(s). (Show the initial Part 1 video again and visualize the enzyme “blob” as being this long chain of amino acids, intricately folded such that side groups are in exactly the right position to attract the reactants and catalyze the reactions that occur. Then visualize the same thing going on simultaneously for 100s of other reactions occurring simultaneously in the cell. 

E.   The last but very important point to emphasize is that all reactions  involving synthesis require energy. Things come apart on their own; to put them together requires energy. (Consider the simple activity of stacking blocks.) The energy aspect is addressed in Part 3.