What must happen before acetyl CoA can be formed during respirtion?

Before acetyl CoA can be formed during respiration, pyruvate must be produced from glycolysis, which occurs in the cytoplasm. This pyruvate is then transported into the mitochondria, where it undergoes decarboxylation by the pyruvate dehydrogenase complex. During this process, one carbon atom is removed from pyruvate as carbon dioxide, and the remaining two-carbon fragment is combined with coenzyme A to form acetyl CoA. Additionally, NAD+ is reduced to NADH in this reaction.