(N/A) The Krebs cycle,also known as the Citric Acid Cycle or Tricarboxylic Acid $(TCA)$ cycle,is a series of chemical reactions used by all aerobic organisms to generate energy through the oxidation of acetate derived from carbohydrates,fats,and proteins into carbon dioxide $(CO_2)$.
$1$. The cycle begins with the condensation of the $2C$ Acetyl group from Acetyl Coenzyme $A$ with a $4C$ molecule,Oxaloacetic acid,to form a $6C$ Citric acid molecule.
$2$. Through a series of decarboxylation and oxidation reactions,Citric acid is converted into $\alpha$-ketoglutaric acid $(5C)$,releasing $CO_2$ and reducing $NAD^+$ to $NADH + H^+$.
$3$. $\alpha$-ketoglutaric acid is further oxidized to Succinic acid $(4C)$,releasing another $CO_2$ and producing $NADH + H^+$. During this step,$GTP$ (or $ATP$) is also generated.
$4$. Succinic acid is oxidized to Malic acid $(4C)$,which involves the reduction of $FAD^+$ to $FADH_2$.
$5$. Finally,Malic acid is oxidized back to Oxaloacetic acid $(4C)$,regenerating the starting molecule and producing another $NADH + H^+$,thus completing the cycle.