How amazing enzymes are

Enzymes are biological catalysts.

Enzymes are proteins.

Galactosidase enzyme
Substrates: maltose, which is broken into two glucose molecules

These two sentences are actually the main way to characterize an enzyme. Firstly, a biological catalyst is a substance that speeds up the rate of the reaction (how quickly it happens per unit time) without changing the equilibrium. Further, enzymes are biological catalysts because they are made within the body. It's actually easy to envision two reactions which are reversible- the products can react to form the initial reactants- to understand what is the equilibrium that I'm talking about and how enzymes are maybe best described as the second hand. That is because the reactants can react together on their own but that would take a long time so enzymes, due to their ability which I would talk about as we progress, come and help with lowering the activation energy( the energy needed for the molecules to engage with each other) without being directly involved. Come to think of it,they remind me of industrial machines which help put and secure the cap of bottles on; they do help but after finishing one bottle they can get on with the cap of the next without being changed.


Secondly, they are proteins. Proteins are biological molecules which are made up of amino acids, which bond through peptide bonds. This is really one of the most exciting thing about enzymes and
proteins: their diversity. We are talking about 20 amino acids bonded together in soo many ways, in polypeptide chains of different length, subjected to change. To understand better the anatomy of an enzyme we need to concentrate on the structure of amino acids.
 They have the central alpha Carbon atom linked to an NH2 amino group, a carboxyl group and finally, a side chain: R. It is mostly the R groups that I will focus on when explaining the complexity and abilities of proteins although the other parts also have their role. Speaking of R groups: they are the only thing that differ between amino acid molecules: all have the alpha carbon, the NH2 and COOH but each of the 20 has a different side chain. (Fun fact,amino acids can be a part of metabolism on their own and some are modified).Thus, the original sequence of amino acids determines the bonds that may form between R groups, which finally confer the protein a specific overall shape and an unique active site as well, in the case of enzymes. The active site of an enzyme is like the mouth of a fish and any food( the substrates) that enters the mouth is broken into pieces. The reactions that an enzyme catalyses are conditioned by the active site: it's shape and the R groups that are found at the site, as they interact with other parts of molecules and help cleave the molecule or create a new one.
This would be a good time to introduce you to the Lock and Key Hypothesis and the Induced Fit Hypothesis- the latter is just a more detailed account of the former. Basically, as already said, enzymes have specific active sites and therefore only a limited range of molecules can fit in. But, it turns out that this site is actually a similar shape to that of the molecules, not an exact lock for the key. Thus, when molecules enter the site they change its shape and this is why it is induced,

Lock and Key

Induced Fit 

Do enzyme always perform? Not really. When they are under the necessary conditions such as temperature and pH and there are no inhibitors they do. Temperature and pH outside the normal range for each enzyme denatures the protein, meaning that the bonds between the R groups are broken and you are left with just the original straight polypeptide. Inhibitors can either bind to the active site,so that the molecules which are substrates cannot enter and thus the reaction will not be catalyzed, or to other parts of the enzyme in a way that changes the shape of the overall enzyme, including the active site.

If we consider how many variations in conditions provided by the body there are, we can appreciate the complexity of enzymes.

Cristina