Carboxylation - what exactly is transferred?

[Lothric]

Hey,

FA says that carboxylation is a process in which carbon dioxide - with the aid of biotin - is transferred to another substance. However, everywhere else it is a carboxyl group (-cooh) that is transferred and not carbon dioxide. Is there a fundamental chemical principe going on that somehow causes carboxyl groups to end up as carbon dioxide or is FA wrong?

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[GoljansRightBicep]

There is a fundamental chemical principle going on here. Carboxyl groups are formed by the electrons attacking the carbon in CO2. Conversely, carboxyl groups can leave the parent molecule as CO2 gas. There is much more organic chemistry going on behind all this, but that is the general gist of things and likely all you'll need for Step 1. But hey, if I have to push some arrows on Step, you won't hear me complaining!

Here's an example of such a reaction. Notice how the double bond attacks the carbon in CO2 gas to form the carboxy group:

And here's a decarboxylation reaction. Notice how the carboxy group leaves as CO2 gas: