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Co-factors, co-enzymes, and vitamins | MCAT | Khan Academy – Transcript
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- Co-enzymes function as organic carrier molecules that hold on to specific groups or electrons to help enzymes make catalysis run more smoothly.
- Co-factors are directly involved in the enzyme's catalytic mechanism by helping stabilize the enzyme or substrates or convert them.
- Vitamins typically refer to organic co-actors and co-enzymes that must be obtained from the diet, while minerals are usually inorganic co-actors.
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today we're going to talk about co-factors and co-enzymes and how sometimes they can be essential to proper enzymatic function but first let's review the idea that enzymes make reactions go faster and they do this by lowering the activation energy peak of their respective reactions let's also review the idea that enzymes bind their substrates at a location on the enzyme called the active site which is where most of the reaction takes
place now not all enzymes are able to catalyze reactions on their own and some need a little help so if we have our enzyme here trying to react with our substrate over here sometimes something called a co-actor or a co-enzyme will be needed which will also need to bind to the enzyme in order for it to function properly and we're going to go over what co-enzymes and co-actors are and exactly how they work so first we'll talk about
what a co-enzyme is well co-enzymes are organic carrier molecules and what I mean where organic is that they're primarily carbon-based molecules and by carrier I mean that coenzymes hold on to certain things for an enzyme to make the catalysis run a little more smoothly and a great example of a co-enzyme is nadh which acts as an electron carrier and here I've shown
nadh dissociating into its oxidized form nad+ as well as to a hydride ion which basically just exists as a pair of electrons that some other molecule would be grab grabbing so nad+ can accept electrons causing the molecule to be converted to nadh which could then carry electrons for an enzyme now if you remember the lactic acid fermentation reaction where pyrovate is converted to lactic acid
you'd see that the enzyme catalyzing this reaction lactate dehydrogenase uses nadh as a co-enzyme in order to transfer electrons to the pyrovate molecule in order to turn it into lactic acid and in this sense nadh is acting as an electron carrying co-enzyme another example of a co-enzyme is co-enzyme a which like nadh acts as a carrier molecule but instead of carrying
electrons like nadh does co-enzyme a which we sometimes call COA holds on to asil or acetal groups instead and you'd see COA appear quite often in metabolic reactions where it'll carry these two carbon acetal groups from one molecule to another now co-actors are a little different from co-enzymes while co-enzymes are only really involved in transferring different things from one molecule to
another co-actors are directly involved in the enzyme's catalytic mechanism they don't strictly carry something like a coenzyme wood but might be stabilizing the enzyme or the substrates or helping the reaction convert substrates from one form to another a great example of this is with the enzyme DNA polymerase remember that DNA polymer is responsible for helping out with synthesizing new
DNA during DNA replication now you may remember that DNA is a very negatively charged molecule because of all the negatively charged phosphate groups that you'll find around it well DNA polymerase uses a magnesium ion as a co-actor which can use its big positive charge to stabilize all that negative charge on DNA and you can see how this is different from a co-enzyme because instead of acting as a carrier molecule
the magnesium ion co-actor is stabilizing the DNA and is more directly involved in the actual catalysis now interestingly what people normally call vitamins and minerals like the kinds that a doctor would tell you to make sure you get enough of in your diet are often different co-actors and co- enzymes and what's special about vitamins and minerals is that your body can't build them up from scratch and you need to get them from your diet in order
to stay healthy so when we say vitamins we typically refer to organic co-actors and co-enzymes so two great examples are ones we just discussed vitamin B3 which you may see being called niin on a food label is actually just a precursor for NAD and vitamin B5 is just a precursor for co-enzyme a minerals on the other hand are inorganic meaning they aren't
carbon based and minerals are usually just co-actors in our body so magnesium would be a great example of a mineral co-actor that an enzyme like DNA polymerase would use now not all minerals Act only as co-actors some minerals like calcium which can act as a co-actor is also a critically important component of bone and teeth and it doesn't strictly act as an enzyme
co-actor here it's actually an important part of the structure itself so what did we learn well first we learn that not all enzymes are able to function alone and some need a little help and next we learn that this help can come from co-enzymes which usually act as carrier molecules or co-actors which directly assist with the catalysis that the enzyme is doing and finally we
learned that vitamins and minerals generally refer to dietary co-actors and co-enzymes