The oxidation of glyceraldehyde-3-phosphate to 1,3-bisphosphoglycerate is an endergonic reaction, but the flow through this point in glycolysis proceeds smoothly. Part A How is the unfavorable equilibrium constant overcome

This inbalance is constantly overcome by the production of excess product (1,3-bisphosphoglycerate) which triggers the reversible reaction through the action of the enzyme called glyceraldehyde 3-phosphate dehydrogenase in the process called gluconeogenesis .  

Explanation:

A cofactor (NAD+) and a phosphate molecule are crucial to this reaction to produce NADH which results in ATP a high energy molecule. an OH ion is removed from the glyceraldehyde-3-phosphate molecule and transferred to the NAD to form NADH molecule and an intermediate (thioester). The Phosphate molecule then binds to the thioester to form 1,3-bisphosphoglycerate