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Introduction to pharmacology
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Enzymes are proteins that play a major role in the biochemical reactions happening every moment inside our bodies - everything from digesting a bowl of ramen noodles to flexing your muscles in front of a mirror.
Enzymes act as catalysts - meaning that they speed up the rate at which these biochemical reactions happen.
So instead of waiting months to years for a reaction to happen, it can happen in seconds - which is essential for life to happen.
Imagine trying to digest a single bowl of ramen for a year - you’d die of hunger before you could do it!
Every biochemical reaction has a substrate and a product - so let’s put them on this graph called a reaction coordinate diagram.
The X axis shows how a reaction progresses, while the Y axis shows the energy level at the different points along the reaction.
In the beginning, we’ve got the substrate - let’s call it A - with a fair amount of free energy.
At the end of it, there’s the product - or B, which ranks lower energy-wise.
The energy of the product minus the energy of the substrate is called the energy of the reaction, also known as Gibbs free energy, or ΔG.
Because lower energy states are preferred, a reaction spontaneously occurs when the product has a lower free energy than the substrate - so a negative ΔG.
So let’s say we’re looking at one such spontaneously occurring reaction, but between going from the substrate to the product there’s an intermediate transition step that has a really high energy state.
The amount of extra energy the substrate requires to get to the transition state - so the height of the upslope - is called the activation energy - or a ΔG‡ plus plus.
As soon as it enters the transition state, the molecule is highly unstable - and wants to go to a more stable lower-energy molecule
It either goes back to being a substrate or to being a product.
If it’s a substrate once again, it can go back up to the transition state if there’s enough activation energy once more, but if it becomes a product then it needs even more energy to get back to the transition state.
That’s why over time, with millions of molecules doing this, the majority of substrate turns into product.
Now, without an enzyme, the substrate might eventually harness enough activation energy to enter the transition state - but enzymes help speed things up quite a bit.
Enzymes are proteins that are folded in a particular way, so that they have a pocket called the active site on their surface.
When enzymes get involved in a reaction, the substrate binds to the active site, and together they form an enzyme-substrate complex, and that helps stabilize the transition state.
So enzymes decrease that extra energy requirement for the reaction - graphically turning our mountain into a hill.
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