Enzymes are a fundamental component of biological functions. These proteins both spur and speed up chemical reactions in a body without themselves being changed or affected by those reactions. Enzymes don't contaminate the reactions in any way, either; not by giving up a piece of themselves or changing the results of the reaction.
We often think of enzymes in conjunction with eating and digestion for a good reason; there are plenty of different enzymes to help break down our food to extract nutrients. But that's not enzymes' only job.
Practically all metabolic processes any cell undertakes need enzymes to act as catalysts so that the required chemical reactions will happen fast enough to sustain life - both the cell's life and the organism's.
They are satisfyingly specific and weirdly sensitive to temperature, as well as to anything that might inhibit their function or, conversely activate them. You know all about enzyme activators, right?
Considering enzymes' importance, both to biological functions and you earning good marks on your GCSE Biology, Superprof goes into the topic in depth.
An Overview of Enzymes
Enzymes' function is to speed up chemical reactions within an organism. These proteins are not changed by the reactions they help induce, nor do they have any impact on the chemical reactions, other than bringing them about and accelerating them.
Enzymes are 3-dimensional shapes specifically designed to accommodate particular molecules. In other words, the enzyme lipase is built to break down only lipids; they cannot 'unlock' proteins or sugars.
This specificity is called the lock-and-key hypothesis.
The way enzymes are built incorporates what is called 'active sites', the part of the enzyme that works on the molecule it is designed to deconstruct. The process works a bit like sticking a key into a lock - hence the hypothesis name. Of all the keys on your keyring, only one key will unlock your house, your bike, or your school locker, if you have one.
You can't use your bike lock key to unlock your house, or vice versa, right? Enzymes operate on the same principle.
Unlike cells, enzymes are not alive; as such, they cannot be killed. However, they can be denatured. For instance, their shape may change when subjected to higher-than acceptable temperatures. Heat above their tolerated range alters their active site, leaving them unable to fit the substrate molecule into its allotted space.
Exposure outside their specific pH range will also denature an enzyme. That's why plant and animal nutrition is such a critical area of study; any intake that radically changes an organism's chemical makeup will have a grave impact on how the organism functions.
What Enzymes Do
You likely already know from your studies that enzymes play a significant role in breaking down and digesting food. Did you also know they are instrumental in cell communication, metabolism and movement in animals? As an example, Adenosine Triphosphate - ATP works as a coenzyme to cause muscle contractions.
Enzymes are vital to cells' ability to send signals along their signalling pathways that result in necessary cellular responses - say, regarding metabolism, cell growth or the transcription/translation of genetic information.
Enzymes also work together to create metabolic pathways; this is a rather sophisticated process wherein one enzyme's product becomes the next enzyme's substrate, creating a sequence of 'breakdowns' until the desired product is achieved.
You might visualise that process as something similar to a production design firm: one team comes up with a concept, one designs the steps to make it a reality, a few teams manufacture the components, and the production crew creates the finished product.
For all of their power and necessity, enzymes do not call all the shots. Indeed, organisms have many layers of control to keep enzymes in check:
- activation/inhibition: the final product of a metabolic pathway controls how much product will be made
- post-translational modification: a process that keeps the enzymes from digesting other tissues
- translation/transcription of enzyme genes keep them impervious to outside chemical influence, for instance, antibiotics and other drug interactions
- sub-cellular distribution keeps enzymes compartmentalised for maximum effectiveness
- organ specialisation regulates the organism's overall metabolism
Keeping enzymes in check ensures homeostasis - the ongoing health and balance of the organism. Any mutation, deletion or over/underproduction of any enzyme could lead to a debilitating genetic mutation that could endanger the organism's life.
Another factor that could seriously impact an organism's wellbeing is cells' ability to respire and expel gases. Here, too, enzymes play a role...
Factors That Affect Enzymes
Enzymes are pretty tough and fairly versatile but they do have their Achille's Heel - three of them, to be specific. Let's take a close look at each of them.
If enzymes have plenty to work on, they will work most efficiently. So, the more concentrated the substrate is, the more efficiently the enzyme will process it. If the concentration of substrate increases, so does enzyme activity - but only to a point.
The best comparison would be sensible versus latent heat.
As heat increases, you can feel (sense) the incremental differences. However, once the heat has reached peak sensibility, it becomes latent - we know it's there but we can't measure it.
Enzymes in substrate saturation conditions show the same phenomenon. There's more substrate to work on but the enzymes, having reached peak efficiency, cannot work through it any faster.
Enzymes are designed to work in specific environments and exact acidity. For instance, enzymes found in the stomach, which have an optimal pH level of 2 - very acidic, would not work well in the gut, which has a pH level of 7-8 - a more balanced pH value.
The amylase found in the pancreas, the liver's catalase and cholinesterase (found in red blood cell membranes) all have a pH level of 7. Of these three enzymes, catalase has a relatively broad maximum range, meaning that it can function effectively in a pH environment of 6.8 to 7.5.
Just as with substrate concentration, heat's effects on enzyme activity causes a speedup. Activity plateaus once they reach their optimal temperature range. However, if that temperature extreme is exceeded, enzyme activity will drop off because it will become denatured - unable to function.
That's because excess heat - beyond the range the enzyme can tolerate will cause its active site will warp or change shape, making it unable to effectively lock onto its substrate.
Should any or all of these factors working on enzymes come into play, the organism could become destabilized, resulting in illness or injury - notably, bowel diseases, including a perforated bowel.
Enzymes and Food Groups
Some enzymes can 'unlock' several different substrates but, overwhelmingly, they are specific to the molecules they can break down. Nowhere is that clearer than the processes of food digestion.
Animals eat a variety of foods. Admittedly, the more basic organisms, such as amoeba and hydras consume relatively simple food; thus, their enzyme population is limited. Herbivores - cows and other ruminants, all bacteria and animals with a herbivore diet have an enzyme specifically meant to break down the cellulose of the plants they eat.
Would you be surprised to know that enzyme is called cellulase?
Indeed, many enzyme names reflect the substrate they work on; that makes linking them to their substrate easy. Take protein, for example. Its corresponding enzyme is called protease. A good rule of thumb to identify enzymes is to note any -ase ending. Any word ending that way - lactase, amylase, lipase... indicates an enzyme.
Back to food, now.
The omnivore diet - the diet most humans embrace is rich in lipids, proteins and carbohydrates. They are all necessary for growth and homeostasis - maintaining our bodies' systems but, on the molecular level, they are far too large to pass through the intestinal walls and into blood cells. They have to be broken down.
Proteins are long chains of amino acids that contain hemoglobulin, keratin and collagen. Each of these long-chain amino acids has its own properties; they're each joined in a specific sequence and folded in a particular way.
Proteases break down the proteins we consume, turning them into alternate amino acids for recombination with other amino acids further in the digestive phase. This action takes place in the stomach and small intestine, where this enzyme is concentrated. Protease can also be found in the pancreas.
You might know that the pancreas is where three different enzymes are produced: lipase, amylase and, of course, protease.
Lipids are sterols, glycerides, fat-soluble vitamins and fats. Besides production in the pancreas, lipase - the enzyme that breaks lipids down, is produced in the small intestine.
Carbohydrates are made up of starch, glycogen and several types of sugars, among other molecules. Carbohydrates are rather complex because, while their basic unit is a monosaccharide - a simple sugar like fructose or sucrose, enzymes within the carbohydrates combine these simple sugars into more complex molecules.
Disaccharides and polysaccharides must be broken down into basic units before they can be digested. The enzyme carbohydrase undertakes that process. Carbohydrase is produced in the mouth, pancreas and small intestine.
You might wonder, if so many enzymes are produced in the pancreas, how they get to where they're needed. To answer that question, we need to learn about transport in plants and animals.
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