Cyanide Ion is valuable for organic synthesis. Like Grignard Reagents, Gilman Reagents, Acetylide Anions, Enolate Anions and the Phosphorus Ylides of the Wittig Reaction, Cyanide Ion can serve as sources of nucleophilic carbon, enabling the formation of new carbon-carbon bonds. Subsequent hydrolysis of the cyano function produces a carboxylic acid, or reduction can be employed to produce an amine.

Thiamine pyrophosphate (TPP) is a derivative of thiamine (vitamin B1) that has a nucleophilic activity that is similar to cyanide ion. Thiamine pyrophosphate (TPP) is a source of nucleophilic carbon for addition to aldehydes and ketones. TPP serves as a prosthetic group for three crucial enzymes: pyruvate dehydrogenase (glycolysis), α-ketoglutarate dehydrogenase (citric acid cycle), and transketolase (sugar interconversion mechanisms).

The biochemistry here is beyond the MCAT scope as required, prior knowledge for the exam. What I am trying to help you build is a network of coherence to bridge your organic chemistry and biology. For biochemistry and the MCAT, fundamental concepts and intuition are more important than the multitude of detailed pathways.