Molecular Biology

What are Enzymes



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Enzymes are proteins that enable or increase the rate of chemical reactions in the body.  But where are they produced and how do they work?

Enzymes work as catalysts in a chemical reaction and that means that they get involved in bringing together the chemicals that need to react together.  By bringing the chemicals, called substrates, closer together the enzymes enable the reaction to take place.

The structure of enzymes
All proteins are complex molecules which have a distinct three-dimensional structure.  They typically consist of long strands of polypeptides all wrapped around each other and the three dimensional shape is important.

The shape of the enzyme molecule dictates what substrates it can interact with.  If the shape is not right, then that substrate will be ignored and only those particular molecules that "fit" the enzyme will be affected.  That makes enzymes very specific and their structure equips them for specific jobs, for accelerating specific reactions.

Enzymes have active sites on their 3-D structure which can bind to one of the substrates.  The binding typically adjusts the 3-D structure so that the molecule can also bind to the other substrate bringing them together.  Because of the proximity of the reactants, the chemical reaction can take place much faster than if the substrates were both free moving, typically millions of times faster.

More complex protein molecules may have an even more complex structure being composed of several units, each of which have their specific 3-D structure and the size of enzyme molecules can be very large.

Within the body, there are around 4000 chemical reactions which are speeded up by enzymes and without them, our biochemistry could not function.

Enzymes don't get used up
Because they don't actually get involved in the chemical reaction themselves, once the substrates have reacted, the enzyme molecule releases them and can be used again and again.  In digestion, the same enzyme molecule is used over and over in the breakdown of our food, so the enzyme itself is not consumed in the course of the reaction.

Of course, in some biological processes such as digestion, there is a natural loss of some enzymes.  Because some enzymes pass out of the gut, they need to be replaced and so organs will produce more of them.  The stomach will produce enzymes such as rennin for digesting proteins, the small intestine will get enzymes delivered from the pancreas such as amylase and trypsin.

Enzyme inhibition
It is important that enzyme activity is controlled to prevent reactions occurring spontaneously everywhere.  There are molecules which bind to the enzymes subtly adjusting their shape so that the active sites are not longer available.  These molecules are called enzyme inhibitors and they perform a valuable control function.

The common drug aspirin works by enzyme inhibition helping to suppress pain and inflammation.  But the poison cyanide also works by enzyme inhibition with fatal consequences.

Enzymes in biochemical pathways
The metabolic pathways are those routes taken when our foodstuff are broken down to extract energy, and also to use the components to build other more complex molecules that we need.  In all of the pathways, enzymes are essential.  Whether it is breaking down carbohydrates to simpler sugars, or building up fatty acid components into hormones, enzymes do the crucial work of enabling the reactions to take place.

Protein manufacture is based on transcribing the patterns in RNA into a sequence of amino acids.  But if there is a mutation in the RNA, then the resulting structure can be wrong.  It may be that the enzyme still functions but reacts with the wrong substrate.  Or perhaps it will not provide sufficient acceleration in the reaction.  Such mutations can produce enzyme-related illnesses.

Enzymes in daily life
Biological enzymes are also used in washing powders to break down biological stains.  Since they are proteins, enzymes are sensitive to high temperatures and typically get denatured at sixty degrees.  

But enzymes are also routinely used in the food industry, in the brewing industry, and even in the paper industry.  Biological enzymes are remarkably specific in their selection of substrates and this means they can be used to fine tune chemical processes as well as speed them up.

The study of enzymes

We now know a great deal about the many enzymes in the human body including the sequence of amino acids that make them up, their three-dimensional structure, the active sites, the inhibitor and control mechanism, and the factors which affect their activity.  We are also increasingly able to relate this activity to the expression of genes from DNA through RNA and this provides insight into genetic diseases as well as illness caused by imperfect replication mechanism.

Enzymology is an important medical science which offers the prospect of clinical treatments for diseases that have so far resisted investigation.  This includes cancer, brain disorders such as Parkinson's Disease, and also neurological diseases.

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