Monday, September 20, 2021


Biology Index

Where are we going with this? The information on this page should increase understanding related to this standard:  Evaluate comparative models of various cell type…Evaluate eukaryotic and prokaryotic cells.

Article includes ideas, images, and content from Troy Smigielski (2021-09)

(Hey! This rings a bell!)

Nearly all enzymes are proteins that serve as biological catalysts. In chemistry (and biochemistry), a catalyst is a substance that, though not actually a part of the reaction, increases the rate of a chemical reaction without, itself, being permanently changed. Enzymes do this.

Another way to say it is that enzymes accelerate chemical reactions between different biological molecules. The molecules that the enzymes operate on are called substrates.

Source, 2021-09-21
Each enzyme is very selective with regard to which process it speeds up
. The "lock and key" analogy is a good way to think about this. 

In this analogy, the lock is the enzyme and the key is the substrate. Only the correctly sized key (substrate) fits into the key hole (active site) of the lock (enzyme).

Smaller keys, larger keys, or incorrectly positioned teeth on keys (incorrectly shaped or sized substrate molecules) do not fit into the lock (enzyme). Only the correctly shaped key opens a particular lock. This is illustrated in graphic on the left. Source, 2021-09-21

Enzymes can break compounds down or put molecules together.

Most enzymes end in -ase. (Not to be confused by mayonnaise! Same sound, different spelling…)

The molecular shapes of enzymes are specific to the substrates with which they work. As was mentioned, enzymes only work with specific substrates. 

Look at the image to the right. The shape of the enzyme determines which molecules it can work with.

The enzymes pictured would be those that put molecules together to create a compound. Would it be possible for the enzyme on the right to work on one of the circles? Why or why not? No. The shape of the enzyme specifically works only with certain other molecules with a matching shape.

Each enzyme has an active site on it that recognizes a specific substrate.
  • The active site is a region on the enzyme.
  • The substrate is the molecule being acted on.

Once the active site binds to the substrate, the molecule becomes the enzyme/substrate complex. Small changes occur that help the enzyme fit tightly to the substrate. This is called the induced fit model.

Using a workshop as an analogy for enzymes, you could think of an enzyme as a clamp or jig. Parts could be held in the jig or clamp until glue bonds them together (or until a solvent separates them).

This enzyme is breaking a compound apart.

Inhibitory Molecules

Occasionally, an inhibitory molecule can cause the enzyme to not function. There are 3 kinds but we will focus on 2:
  • Competitive inhibition: when a fake substrate binds to the active site which prevents the real substrate from attaching

  • Non-competitive inhibition: when a molecule attaches to the enzyme at a place other than the active site

Enzyme Use

Enzymes are reusable which means they are able to function over and over again. This happens until they are destroyed or denatured.

Enzymes are influenced by 4 main environmental factors:
  1. pH (measure of acidity)
  2. Temperature
  3. Amount of substrate
  4. Salt concentration
Each enzyme will have operational range and an optimal range for each of the environmental factors. Outside the operational range, they will not work. They work best when within their optimal range.

The graph to the right shows a sample of the effect of pH on enzyme activity.

At pH below approximately 1.75 and above approximately 11.75, the enzyme won't work.

It works best between a pH of roughly 6 to 7.

Based on how the enzyme behaves under different pH readings, we can determine both the optimal range and operational range.

Like pH, temperature rages affect enzyme effectiveness. 

Low temperatures cause reactions, in general, to be slower. This is also true with reactions catalyzed by enzymes; enzymes are less effective at low temperatures.

However, if the temperature gets too high, the enzyme will deteriorate (they become denatured). When this happens, the active site no longer fits with the substrate and the effectiveness goes down until it simple no longer works.

Another factor is the presences of substrate. Substrate concentration is an indication of how much substrate is present. 

If there isn't any substrate, the enzyme doesn't have much to do.

Imagine an assembly line that can put together 100 toy cars in an hour. It doesn't matter how fast the assembly line is if there are no wheels to put on.  If there are only 8 wheels, only 2 cars can be built.

If there are 8,000,000 wheels, then the assembly line can make 100 cars in an hour, but no more.

So, there is an increase in enzyme activity up to some level of concentration. After that, the enzyme is running at full speed.

Enzymes and Cellular Transport

How do enzymes relate to cell transport? The cells in your body are in constant demand of various compounds for various reasons, and these compounds are often created by enzymes before they can enter and exit your cells.

Your body needs ATP (energy) to play a guitar. How does it get that?
  1. You eat mashed potatoes which are full of starch (a polysaccharide).
  2. Amylase is used to break down starch into glucose.
  3. Glucose is taken up into your cells by the protein insulin.
  4. Glucose mixes with oxygen and goes through a series of reactions. 
  5. At the end of this series, ATP Synthase creates ATP which gives your muscles the energy to strum.


Enzymes are proteins that serve as biological catalysts. 

Enzymes accelerate chemical reactions between different biological molecules. 

The molecules that the enzymes operate on are called substrates.

Each enzyme is very selective with regard to which process it speeds up.

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