## Introduction #

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Basically everything in life has an orchestrator. The reason why those at the south pole or even at the western or eastern regions of the globe do not just fall off into space is **gravity** (or maybe, we just have sticky feet lmao). It sort of keeps us glued to the earth. It is also the same reason why when you throw a ball up, you can keep your hands open hoping to catch it knowing it will come down. **Gravity** yet again gave you that assurance. Without the mitochondria, cells will not be able to generate energy for their day to day activities. They will eventually die because energy is indispensable and essential for the survival of living organisms. Let me say there are guys, predominant in nature, who do a lot of work behind the scenes but take little or no credit for it. In biochemistry, I know a group of those guys. They are called **Enzymes**

# ## Let Us get To Know These Guys Who Do Most of the Biological Work and Get Little Recognition. #

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Let me take you down a certain path of realization. You are a multicellular organism. Okay, this means that you are basically just a mash up of cells which happens to be organized well giving you as the overall product. You continuously synthesize cool molecules which you need and well, you are not set up like a factory (literally !). You also breakdown complex stuff like the tough carbohydrates (starch) and get what you survive on (glucose) from them but you are not set up like a machine that breakdown stuff. This apparently means that there is perhaps something which has conferred on you this ability.

This is no voodoo or magic. You just happen to have a couple of cool guys known as **enzymes**. I can give you some credit because you make these guys anyway. These cool guys are proteins. We however have a few which are not proteins. Just a few. So I can still say enzymes are proteins and sound politically correct. Whatever. I do not seek political correctness. I want to remain as factual as possible. So, most of these cool guys are proteins. A few are not. So what are they ? RNA molecules actually. Yeah, an example is the **Ribozyme** which can pretty much what protein containing enzymes can. Okay so now you know there are cool guys that give you special abilities like digestion, biosynthesis and breakdown and what not. Let us proceed to knowing what they look like.

# ## What Do These Cool Guys Look Like anyway ? #

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Enzymes are proteins so they are gonna look like proteins. They are made up of amino acids arranged in sequences as regards the particular enzyme. These amino acids need to be arranged pretty much well as encoded in the RNA transcript so as to maintain the cool property (catalytic activity) of the enzyme. They are mostly synthesized in their proactive forms. In this form, they are known as **zymogens or proenzymes**. They are activated when needed either by cutting off some parts of them (these parts block their catalytic abilities by some mechanism), a process known as cleavage. Having enzymes in their inactive form and activating them when needed has proven time and time again to be very crucial.

It is the reason why trypsin which acts on proteins can be produced by the pancreas exported to the small intestine without eating up (digesting) the pancreas. The inactive form (trypsinogen) moves to the small intestine to be activated only when necessary.

So I have established that enzymes are produced and maintained in their inactive forms. Well, they also have special compartments in them that need to bind to what is referred to as **substrates**. They bind to substrates and find the easiest way to transform them (they find the easiest route for a reaction to follow). Those special compartments are referred to as **active sites** and they are peculiar to each enzyme. It is therefore of no wonder why there are lot of these cool guys (way more than a thousand).

These cool guys are also specific in their action. In that they stick to one mate. Actually, they bind specific substrates so it’s difficult to see an enzyme possessing the ability to bind two or more different substrates interchangeably. Trypsin will bind to proteins and nothing else. Glucokinase will bind to glucose and nothing else.

# ## What They Do and How They Do It #

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Enzymes are catalysts and well, that only implies they speed up already existing reactions. Just like catalysts, they remain the same, as they were in the beginning of the reaction, at the end of the reaction. This means that they are not a part of the reaction but influence the reaction from the sidelines.

Enzymes speed up biological reactions by lowering their activation energies. The activation energy is what needs to be overcome before a reaction can take place. Without an enzyme, the activation energy stays the same and some external factors like heat or pressure or both needs to be applied for the activation energy to be overcome and this will take a lot of time as well as energy. This is not thermodynamically favorable and also a huge waste of energy.

With enzymes however, the activation energy is lowered and the reaction can proceed easily and on time. This makes enzymes very important because technically, they speed up reactions. It is the reason you can, after being hungry for hours and feeling so weak, eat food and feel strong again within just minutes. Your digestive reactions are sped up. Thanks to enzymes really.

# ## Death Comes in Threes, Enzymes Come in Classes #

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Just as there are different classes of reactions in biological systems, there are different classes of enzymes. I mean come on, you don’t expect an enzyme that catalyzes an isomerization reaction to catalyze an oxidation-reduction reaction. So the varieties of reactions have given rise to the different classes of enzymes.

The first class of enzymes are the cool **oxidoreductases**. These guys alter the oxidative states of molecules as they wish. I mean they increase the oxidative state of one molecule while simultaneously reducing the oxidation state of another. Cool stuff. A basic knowledge of chemistry will tell anyone reading this that oxidation has to occur in tandem with reduction. It’s more like adding something here and reducing something there to keep everything in check. This is to make sure that equilibrium is maintained as true catalysts (enzymes being one) do not alter equilibrium. An example is Malate dehydrogenase which can catalyze the addition of oxygen (oxidation) and removal of oxygen (reduction) to fumarate yielding malate and fumarate respectively.

The next class of enzymes just like take to stuff from one person and give it to another person. They are known as the **transferases**. They orchestrate the movement of a group from a molecule to another. An example is hexokinase seen in the first step of glycolysis which catalyzes the transfer of a phosphate group from ATP to glucose.

The next class of enzymes are those merchants that like to use water to break chemical bonds. They simply split bonds and place water between them so the bonds do not form again on their own. They are known as the **hydrolases**. Phosphatase which removes phosphate groups from molecules is an example of a hydrolase.

The next guys like to insert double bonds rather than break them. They just simply take out a functional group and add a double bond at that spot. They even go ahead and add groups to double bonds. They just don’t break bonds. They are known as **Lyases**. Deacetylases and decarboxylases are typical examples.

The next guys like to tweak molecules producing alternative structures of them. They are known as the **isomerases**. They move groups around on molecules producing isomers of these molecules. An example are the epimerases which convert glucose to galactose or mannose as the case may be.

The last guys are more like priests or imams as the case may be. They like to join molecules (in matrimony ? Lol) producing bonds (maybe till death do they part). They are known as the **ligases**. An example is Acetyl CoA Carboxylase.

# ## What Do Locks and Keys Have in Common with Enzymes and Substrates ? #

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Well, just like a key always has to fit perfectly with a lock for a door to be successfully opened, a substrate needs to fit perfectly with an enzyme for a reaction to take place. It is however stupid or ignorant to see an enzyme as a lock and a substrate as a key as they do not stay unchanging like locks and keys. Substrates and enzymes change conformation upon binding making a reaction to go through (the induced fit model). This is in opposition to the lock and key model of enzyme-substrate binding where the enzyme structure is assumed not to change but stay constant binding only to tailor made substrate. This is clearly not the case as there is always a change of conformation after binding.

# ## Yeah, Speeding Up Our Reactions is Cool but Do We Always Need To ? #

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No, we do not always need to. Reactions only need to take place when necessary. So enzymes have to somehow be tamed. This gives rise to the concept of inhibition. Competitors can bind to the active sites of enzymes preventing their substrates from binding and making sure reactions do no proceed. This has been hijacked by clinicians and pharmacists enabling the designing of drugs that can act as enzyme competitors preventing certain reactions from taking place. Non-competitive inhibitors bind to a site other than the active site of an enzyme meant for the substrate and prevents a substrate from binding by mostly inducing a change or changes in the active site of the enzyme.

Enzymes can also be regulated by attaching to or removing functional groups from an enzyme which alters the activity of the enzyme. A process known as **covalent modification** or they can just kept in their proactive form and activated when necessary. Anything works ;).

# ## Are Enzymes just Useful in Biological Systems ? #

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No. Enzymes have wide applications outside the biological system. They are particularly seen in industries and in clinical practices. How do you think cheese is made ? Using enzymes like Rennin and Lipase. How do you think detergents are so effective ? Thank the lipases, professed and amylase. How do you think recombinant DNA is made ? Thank the restriction endonucleases, DNA ligases and DNA polymerases. How do you think biomass is pretreated for biofuel production ? Thank the ligninases. How do you think beer is brewed ? Thank the amylases and professes again. How do you think bread is whitened ? Thank the lipoxygenases. The industrial applications of enzymes are very numerous.

Enzymes can also act as markers of diseases. Finding creatine kinase- MM (found exclusively in the muscles) in blood could be indicative of internal muscle injuries. Finding creatine kinase-MB (goofy exclusively in the heart) could be indicative of a heart disease. This is just one of the cases where enzymes play a role in clinical practice. There’s a whole lot of them, trust me.

# ## Final Thoughts #

Enzymes are the molecular workaholics of biological systems and show a particularly amazing diversity. They speed up biological reactions making life possible and also aid in the synthesis of molecules required for survival. They do not get enough recognition but at least they got some today ;).

# ## References # ^{Moore, J. T and Langley, R. (2008). Biochemistry For Dummies. Wiley Publishers. pp. 85-111.
[Enzymes](https://en.m.wikipedia.org/wiki/Enzyme).
Lehninger, A. L., Nelson, D. L., & Cox, M. M. (2000). Lehninger principles of biochemistry. New York: Worth Publishers. pp. 190-238
Chatterjea, M. N. (2012). Textbook of Medical Biochemistry. (8th Edition). Jaypee Brothers Medical Publishers. New Delhi. India. pp. 139-153.

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