Why does the enzyme catalase break down hydrogen peroxide?
In: Biology
TL;DR: catalase *’catalyses’* the breakdown of peroxide by forming a temporary intermediate. The formation of this intermediate has a lower **activation energy** than the normal break down of peroxide. Now, what does that mean?
To understand activation energy, imagine there’s a frog in a slippery bowl, hopping around randomly. Its hops are random in height, but they’re within a range. Most of the time, it’ll land on the side and slide back into the bowl. Sometimes, it’ll hop really strongly, or maybe hop twice back to back, and it’ll make it out of the bowl. The amount of energy the frog has to use to hop out the bowl is the activation energy of it jumping out.
Peroxide naturally breaks down into oxygen and water. But it has a high activation energy. Peroxide molecules are all bumping into each other randomly, and transferring energy as the do so. Every now and then, one molecule will get enough energy, and break down – it’ll hop out of its bowl. If you heat up the peroxide, that’s like kicking the bowl as the frog jumps. It makes it easier for it to hop out.
Catalysis is like adding a step into the bowl. It’s easy for the frog to jump on the step, so most frogs do that. It’s also easy for a frog on the step to jump out of the bowl. But it’s difficult for the frog to jump back *in* to the bowl, step or no step. The result is most of your frogs end up outside their bowls.
So what does the ‘step’ actually look like? Peroxide is H-O-O-H. The O-O bond is not that stable, because oxygen is large and greedy for electrons. This means it needs more than a single bond to safely hold two oxygen molecules together. Also, since oxygen is greedy for electrons, and electrons are negatively charged (like a magnet), there’s a strong negative charge focused right around the O-O bond.
Catalase has a little slot that’s perfectly cosy for a peroxide molecule to fit in. And right in the middle, it has a little nub that’s naturally positively charged. This attracts peroxide and makes it stick around. When the peroxide is in this position, it also pulls on the catalase like a magnet.. This makes catalase fold around it, and shoves one of the H atoms in front of a nub with a negative charge. The result is that H holds onto its electron less strongly, so the adjacent O easily steals it. H-O-O-H becomes H+ (sorta-bonded to one part of the catalase) and O-O-H- (sorta-bonded to another part).
This makes the exposed O happier to lose another electron to its sibling O. So the O-O bond breaks as well. But that negative charge on the oxygen is what was keeping the peroxide in place. This means the now severed H+ and OH- ions are thrown out. They’ll quickly hook up and make water. In the mean time, the O- ion that’s left now has a REALLY focused, strong negative charge.
Which means it’ll gladly attack any nearby peroxide molecules, and break it down by basically ripping an O atom away. This again leaves H+ and OH-, which immediately turn into water. The new O2 molecule is very satisfied with its electron state, and much less electrocally charged, and so is no longer that attracted to the catalase, so it floats off. The result is two peroxide molecules have been turned into one O2 and two water molecules. The catalase comes out of the ordeal same as it started.
Latest Answers