Lock and Key Principle: Definition & Examples |

Maybe you are interested or have been interested in assembling jigsaw puzzles. Your favorite puzzles may be based on the so-called key-lock principle, where the key fits into the lock in many different ways.

You may think the lock and key principle is clever. It’s like the puzzle saying: «Here’s my shape, but you’re going to have to figure out how to fit me into this particular pattern.» That is the unusual and interesting thing about the principle.

The principle of Key-lock principle, what fascinates you also exists in biology. In general, the lock and key principle describes how at least two structures fit together. Such structures, mostly enzymes to substrates, can only fulfill their function if they are connected to each other.

Key-lock principle simply explained

That Key-lock principle describes how exactly two or more spatial structures fit together. Such composite parts can only fulfill their function when they are connected to each other.

This means that the substrate has to match the enzyme present exactly, otherwise the substrates cannot fulfill their function.

You may already have this Key-lock principle belongs, which is mainly related to enzymes. enzyme-substrate complexes are formed according to the scheme of a key and a lock.

Lock and key principle – enzymes

enzymes are biological catalysts that control reactions such as fermentation in all living things. Some enzymes are proteins, others consist of RNA molecules called RNA catalysts or ribozymes.

Not all enzymes are made up of only proteins. Contain many enzymes non-protein parts (cofactors), which can be organic or inorganic. The presence of cofactors is essential for enzyme functions as well as enzyme activitieswhere amino acids are not suitable.

In particular, you need a specific key for your bicycle lock. For the formation of a enzyme-substrate complex the same procedure applies. The substrate binds to the active position of the enzyme. However, only very specific substrates are suitable for the active center of the enzyme. That’s why enzymes are substrate specific.

You can find more information about enzymes in the article of the same name!

active center

the active position of an enzyme is the site of binding of the substrate and the site of reaction between the enzyme and the substrate.

In biochemistry are substrates the substances for the function of biological molecules and the metabolism of organisms.

Any change of conformation the active site alters the suitability of the substrate and thus the likelihood of a reaction.

Lock and key principle in biology

How a specific substrate is detected by an enzyme can be determined using the Key-lock principle be explained. Because the active site of an enzyme is perfectly shaped for a specific substrate, the substrate can only bind in a very specific direction.

In principle, substrate and enzyme fit together like a key in a lock. Thus, binding of the substrate is activated since the shape of the active site matches a site in the substrate.

How the lock and key principle works

Figure 1: Schematic representation of the enzyme-substrate complex

Actually, the name itself describes what you can imagine by the key-lock principle: you have a key that fits exactly into a lock and when you turn it changes it so that something can be opened. This principle can also be applied to the biochemical level.

An enzyme has the task of catalyzing the chemical reactions that a cell needs for self-sufficiency or for the transmission of stimuli. However, for an enzyme, a chemical reaction is not always the same as a chemical reaction. Because of its substrate specificity, it only works with certain substrates. And so that not every substrate can simply dock onto an enzyme, this is what happens Key-lock principle for use.

Every enzyme has one active center. This is shaped in such a way that only substrates specific to the enzyme can bind to it. The molecules of substrate and enzyme are complementary to each other and therefore fit together like a key in a lock.

If the substrate binds to the active center of the enzyme, the enzyme-substrate complex. The substrate is then brought into a transition state where an enzyme-substrate complex is formed and the product can be released.

The key-lock principle was discovered in 1894 by the chemist Emil Fischer.

enzyme inhibition

Not only the substrate can bind to the enzyme, but also a Inhibitor. There are two types of this: competitive and allosteric inhibitors.

Competitive Inhibitors bind to the active site of an enzyme. In addition to the active center, the enzyme has another binding site: the allosteric center. Bind to the allosteric center of the enzyme allosteric inhibitors.

Competitive inhibitors are therefore structurally complementary to the active site of an enzyme. Thus, the inhibitor can bind to the active site of the enzyme.

In contrast, allosteric inhibitors are complementary to the allosteric center of an enzyme. These two types of inhibitors can inhibit enzymes in two different ways.

You can learn more about the process of each enzyme inhibition in the articles on competitive inhibition and allosteric inhibition.

That induced fit-Model related to the key-lock principle

Figure 2: Illustration of the induced fit model

After the discovery of the lock and key principle proved important to enzyme research, Daniel E. Koshland Jr. went one step further in 1958 and expanded the principle using the induced fit-model. He found that in many enzymes the active center only adapted to the substrate when it was already bound to the enzyme. The enzyme can thus already recognize the substrate upon binding and adapt its active center accordingly so that a stable enzyme-substrate complex can be formed.

More examples of the key-lock principle

Every virus, every hormone, every antibody has specific protein structures on the surface. The surface structure is recognized by certain enzymes or antigens. Enzymes or antibodies have a structure that corresponds to the surface of the complementary substance.

The key-lock principle is also used in drug development. This is the only way to determine that an active ingredient in the drug only attacks specific areas.

hormones

Hormones are messenger substances that are produced in various endocrine glands throughout the body and then distributed through the blood to all cells. Hormones are effective in very small amounts. Each hormone has its own form and can therefore only trigger a reaction in certain cells. Such cells possess receptors and are target cells. The receptors are the places where specific hormones can bind.

Hormones and receptors belong together like a lock and key. Fine-tuning a hormone to a specific receptor is an example of the lock and key principle. Only when the hormone matches the receptor and binds to it does it trigger a corresponding reaction in the cell. If the appropriate receptor is missing, no binding can take place and no reaction can take place in the cell.

Figure 3: Specific hormone-receptor binding

Example insulin

Insulin is made in the pancreas and secreted in the body after eating. Its job is to ensure that the glucose can get from the blood into the body cells. Insulin is therefore the key to the lock of the cells – this is how the glucose can get into the cell interior.

Example adrenaline

Adrenaline, a stress hormone, on the one hand causes a reduction in blood flow in the gastrointestinal tract, on the other hand it has the opposite effect in the skeletal muscles. Blood circulation is stimulated in the skeletal muscles.

immune system

Antibodies play an important role in fighting antigens in your immune system. They bind to the surface structure of the antigens according to the key-lock principle in order to render them harmless. The binding specification is so important because otherwise the antibodies would also bind to the body’s own proteins and would thus practically fight against their own cells. Such a case is also referred to as an autoimmune disease.

Key-lock principle – the most important things at a glance

  • The lock and key principle is used in many different processes – for example with enzymes, hormones and antibodies.
  • It states that, among other things, an enzyme only accepts a substrate if it has the right structure. If it doesn’t, there is no bond and therefore no effect.
  • That induced fitmodel extends this principle: According to this, enzymes often only adapt their binding site (the active center) when the substrate is already bound.

proof

  1. Karp (2005). Molecular Cell Biology. jumper.
  2. Ambrose, Easty (1974). cell biology. Academy Publishers.
  3. Birch (2016). 50 Key Ideas Chemistry. jumper.
  4. Planet-wissen.de: How hormones work (06/02/2022).