glucose + glucose --> maltose + water

Question

the ΔG for the following reactions is 4.0 kcal/mol:

 

glucose + glucose --> maltose + water

 

if ATP were used to drive this reaction (ΔG for the hydrolysis of ATP is -7.3 kcal/mol).

what would the overall ΔG be? draw the reaction using structural formulas.

Answer 1

Think about it this way. You want 2 glucose molecules to go through a dehydration process to form maltose and water, but since the process is anabolic (requires energy), you need to use a catabolic reaction (one that releases energy) to "pay" for the energy of the reaction. It's like selling a house to buy a car. Since the hydrolysis of ATP is catabolic (-7.3 kcal/mol tells us the reaction is spontaneous, or more likely to occur, denoted by the negative), ATP is used to "pay" for anabolic reactions. To find the overall ΔG for the reaction, simply add the Δ values together. (Like selling the car for -7.3 thousand and buying the car for +3.3 thousand) To draw the reaction, you will have to remember to draw two glucose molecules and whatever molecule is phosphorylated with ATP, then the products. 

Let me know if this helps.