Editor’s note: Physicians have a special place among the thinkers who have elaborated the argument for intelligent design. Perhaps that’s because, more than evolutionary biologists, they are familiar with the challenges of maintaining a functioning complex system, the human body. With that in mind, Evolution News & Views is delighted to present this series, “The Designed Body.” For the complete series, see here. Dr. Glicksman practices palliative medicine for a hospice organization.

In this series so far, we’ve looked at what makes up the human cell and what it needs to do to stay alive. We learned that, because they constantly threaten to alter the cell’s chemical content and volume, the natural powers of diffusion and osmosis must somehow be combated. The cell has come up with an innovation to do exactly that. It has millions of sodium-potassium pumps in its plasma membrane that constantly push sodium back out of the cell and bring potassium inside. While thus maintaining its chemical content, the cell is also able to control its volume by preventing water from entering by osmosis. To accomplish this task and all of its other vital functions, the cell must have enough energy.

It’s important to understand that every biochemical process in the body requires enzymes to work properly. So, before you can learn about how the cell gets the energy it needs to live, grow and work properly, you must first learn about enzymes.

Enzymes are special molecules (mostly proteins) that are made in the cell and help other molecules undergo chemical reactions when they come in contact with each other. When these reactions occur, energy is either released or used up, and different molecules are produced. Molecules are made up of atoms joined together by chemical bonds. There are very small molecules, like molecular oxygen (O₂), which comprise two oxygen atoms joined together, and water (H₂O), which is made up of two hydrogen atoms joined to one oxygen atom. There are also slightly larger molecules, like glucose (C₆H₁₂O₆), a sugar that is made up of six atoms of carbon and oxygen joined to twelve atoms of hydrogen. And there are very large molecules, like carbohydrates, fats, and proteins, many of which are made up of hundreds or even thousands of atoms joined together.

When molecules meet up with each other they sometimes react. A reaction between molecules simply means that chemical bonds between atoms are created or destroyed. This usually causes some of the atoms in the reacting molecules to change places with each other to form different molecules. Some enzymes help destroy chemical bonds in larger molecules, to form smaller molecules. Other enzymes help create chemical bonds between smaller molecules, to make larger ones.

In this process energy may be released or used up. At the end of the reaction the enzymes are not altered, so they can continue to promote more reactions. Also, the total number of atoms present in the molecules that are produced at the end of the reaction is the same as there were in the molecules that reacted in the first place. In other words, in a chemical reaction no new atoms are created or destroyed, just the bonds between them. This often results in the release or use of energy, and the atoms involved changing partners to form different molecules.

The laws of nature determine how fast specific molecules will react with each other. But the addition of an enzyme makes this reaction take place much faster. By speeding things up enzymes help to produce many more new molecules, usually on the order of thousands or millions of times more, than what would otherwise happen in the same time frame. This is why enzymes are called catalysts. In fact, if our body were left to only the natural laws of chemistry, the thousands of reactions we need to help keep us alive would not take place fast enough and we would die.

There are thousands of different enzymes in the body. Each has a specific effect on a specific molecule. It is the precise shape and chemical nature of the enzyme that determines which molecules it works on and what type of reaction it catalyzes.

The first part of the chemical name of an enzyme usually indicates the molecule or class of molecules for which it speeds up reactions. The last part of its name usually ends in "ase". For example, lactase is the enzyme that helps to break down lactose, the sugar in milk. A protease is a class of enzymes that helps to break down proteins that are made up of two or more amino acids bonded together.

The body often uses several specific enzymes in a specific order or pathway, like in a chain reaction. The first molecule undergoes a reaction catalyzed by the first enzyme, and one of the products of that reaction becomes the second molecule in the pathway. The second molecule, in turn, undergoes a reaction catalyzed by the second enzyme, and one of the products of that reaction becomes the third molecule in the pathway.

The third molecule undergoes a reaction catalyzed by the third enzyme, and one of the products becomes the fourth molecule in the pathway, and so on. This process continues until the required molecule is produced. If any one of the enzymes in the pathway were to be missing or not working properly, then not enough of the final product would be produced and life could hang in the balance.

It is important to understand that since enzymes themselves are made up of hundreds or thousands of atoms chemically bonded together, the laws of nature can affect their chemical stability and capacity to work properly. Things like temperature and hydrogen ion concentration can affect the chemical structure of enzymes. When any of these parameters falls out of the normal range, the enzymes in our body start to malfunction and so does our body. Serious deviations can even result in death. That is why our body must be able to control these and other vital parameters to allow us to survive within the laws of nature.

Now that you have a basic understanding of what enzymes are, why they’re important for life, and how they work, we can move to see how the cell uses enzymes to get the energy it needs to survive.

Image by Jkaeelwes (Own work) [Public domain], via Wikimedia Commons.