Chapter3: Carbohydrates
Section: Chapter Questions
Problem 7SC
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Transcribed Image Text:Part II - Lactase Catalyzes the Hydrolysis of Lactose
II.i-Enzymes and Sugars
The group of college students is on their way to the ice-cream shop and Sanjeet has offered Xiao-Ma Lactaid so that
she could go with the group and also eat ice cream despite her lactose intolerance.
Xiao-Ma: I've never taken Lactaid. What is it?
Sanjeet:
Chris:
Sanjeet:
My mom told me that you become intolerant to dairy because you don't have the enzyme that can
digest lactose, which is the sugar found in milk products. Lactaid is a dietary supplement that contains
the lactase enzyme.
Uh, Sanjeet, remember-I'm a literature major. What's an enzyme? I don't remember what that word
really means. Also, is the sugar in the milk different from the other sugar in my food?
Finally my biochem class comes in handy in real life! An enzyme is a protein which catalyzes a reaction
in the cell. There are tons of different enzymes in your body. The lactase enzyme catalyzes the degrada-
tion of lactose into its subunits. Lactose is a sugar and there are several other sugars; the one that you
probably know is sucrose. Sucrose consists of two parts: glucose and fructose. Lactose is a different kind
of sugar and consists of glucose and galactose.
You need to digest lactose into the two components because the cells in your intestine can only take up
galactose and glucose but not lactose. If lactose stays in the intestine and is not digested into its com-
ponents, it will be consumed by gut bacteria which produce various gases in the large intestine-that's
what leads to the symptoms Xiao-Ma and I experience when we consume dairy.
Here's a picture from my biochem book showing how the lactase enzyme breaks down the milk sugar
lactose into its components glucose and galactose:
Lactose
OH
CH₂OH
OH
OH
O
CH2OH
OH
O. OH
OH
Lactase
(enzyme)
Glucose
Galactose OH
CH₂OH
OH
HO
-O OH
OH
CH₂OH
OH
-O. OH
OH
Figure 2. Action of lactase.
It also says in here that you can test if you are intolerant to dairy (so lactose intolerant) by measuring
the level of glucose in your blood after drinking milk.
Transcribed Image Text:5. Would you expect higher or lower glucose levels for dairy tolerant individuals after consuming milk? Why?
Draw your predictions for a lactose tolerant and lactose intolerant person into the graph below and explain why.
Glucose (mg/dL)
170
160
150
140
130
120
110
100
90
80
0
Blood Glucose after Drinking Milk
20
40
60
time (minutes)
80
100
120
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