Many saccharides are comprised of smaller, single monosaccharides. Lactose is a

Question

Many saccharides are comprised of smaller, single monosaccharides. Lactose is a carbohydrate fitting this description as it is a disaccharide composed of a one galactose and one glucose molecule. The hydrolysis of lactose into its constituent monosaccharides has a DGo’ of

- 4.0kcal/mole.

a) Write the conversion factor used in the calculations for this project. (2 points)

___________________ calorie(s) = ___________________ joule(s)

b)         Calculate Keq’ for the hydrolysis of lactose. You must show the complete calculation

            including units for full credit. (6 points)

                        Keq’ = ______________________________________

What are the values of Keq’ and DGo’ for the synthesis of lactose from glucose and

            galactose? You must show the complete calculation including units for full credit. (6 points)

                        Keq’ = ______________________________________

                        DGo’ = ______________________________________

d)         Inside a cell, a substance called, UDP-galactose, is actually reacted with glucose in order to

            form lactose. This reaction is catalyzed by the enzyme, lactose synthase. Since the DGo’ of

            hydrolysis for UDP-galactose is – 7.3kcal/mole, calculate DGo’ and Keq’ for the reaction:

glucose + UDP-galactose - - - > UDP + lactose

            You must show the complete calculation including units for full credit. (6 points)

                        DGo’ = ______________________________________

                        Keq’ = ______________________________________

THIS IS A BIO CHEM SUBJECT

Explanation / Answer

a) 1 Cal -------------> 4.184 Joules (J)

DG = -4000 cal x 4.184 J/cal = -16736 J or -16.736 kJ/mol

b) DG = -RT lnKeq   Let's assume T = 25°C or 298 K.

lnK = 16736 J/mol / 8.3143 J/mol K x 298 K

lnK = 6.754756723 ------> K = e(-6.754756723) = 858.13 = Keq

c) In this case, you need to know that the reaction:

Lactose + H2O ----------> Galactose + Glucose DG = -16.736 kJ/mol

In the reverse case, you only need to invert the sign of DG, so: DG° = 16.736 kJ/mol

Applying the same formula as part b):

lnK = -16736 J/mol / 8.3143 J/mol K x 298 K

lnK = -6.754756723 ------> K = e(-6.754756723) = 1.1653x10-3 = Keq

d) In this case, with the DG° of hydrolisis, we do the same thing as part c):

DG° = -7300 cal x 4184 J/cal = -30543.2 J or -30.5432 kJ/mol

LnK = 30543.2 J/mol / 8.3143 J/mol K x 298

LnK = 12327.43102 ------> e(12327.43102) = 225,805.8911 = Keq

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