Lactase Persistence I Scream For Ice Cream 2024

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Texas A&M University, Kingsville *

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Apr 3, 2024

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This showld b'. ean Student's /] 0 maVidual | Scream for Ice Cream: Lactase Persistence in Humans by Nadia Sellami, Julie A. Morris, and Sheela Vemu Name Introduction It is finals week on college campus and everybody is in the middle of studying for exams, just waiting for summer break. Bjorn, Chris, Esiankiki, Xiao-Ma, Sanjeet and Linda are studying together in the international students dorm. Bjorn: Hey, how are you doing with studying? I'm tired ... Chris: Me too. Let’s take a break. I could also use some ice cream after that last final I bombed. Esiankiki: Did I hear ice-cream? I love ice-cream! Let’s go downtown and find a spot. Is everybody coming? Let’s go! Xiao-Ma: Hm, I can’t tolerate dairy so I usually don’t get ice-cream or other milk products. Sorry guys, I'll stay behind. Linda: What does that mean? Do you just not like milk? I used to hate milk as a little kid. Xiao-Ma: No, I actually get really bad stomach cramps, bloating and diarrhea from milk. It’s not pretty. My whole family is that way. When we were still living in China, it wasn’t a big deal because we don’t tradi- tionally eat a lot of milk products there. Sanjeet: Same for me! I get the same thing, and in India we don't eat a lot of dairy either, so it’s not a problem if I eat Indian food. My mom gave me Lactaid® though, so that helps me to eat ice-cream. Xiao-Ma, I can give you some. Let’s go! Nadia Sellami is DBER Fellow and Lecturer, Department of Life Science Core Education, University of California Los Angeles. Julie A. Morris is Assistant Professor, Department of Biological Sciences, University of Denver, CO. Sheela Vemu is Intructor, Department of Mathematics and Sciences, Waubonsee Community College, Sugar Grove, IL. Case copyright held by the "o e or : Teaching in S -, University at Buffalo, State University of New York. Originally published October 3, 2016 Please seeour couo e Wthh outline our policy concerning permissible reproduction of this work. Licensed image ©butsayal?2 | Fotolia.com, 1 74712159.

Part | — Geographical Variation in Tolerance to Dairy 1.i— Survey of Dairy Intolerance Bjirn: Wait, so are you saying that where you're from, people are generally not able to digest milk? At home in Sweden, we eat dairy products like milk and cheese all the time and everyone I know seems to tolerate it well. Linda: That’s so interesting! I'm curious to see how that maps to the wortld and if what you observed could be generally true. Let’s do a survey in the international dorm and find out who is tolerant to dairy and where they are from. I'll put a black dot for a dairy tolerant person in his or her home country and a white dot for a dairy intolerant person. I'll start with Xiao-Ma—one white dot in China! Middle East 2 ast ' Legend Africa - @ Lactose tolerant QO Lactose intolerant Figure 1. Survey of dairy tolerance. Linda’s results on a map of the world Questions 1. Do you see patterns in the geographic distribution of the black and white dots? Describe the pattern qualitatively. 2. How would you quantify these patterns? (2—) “I Scream for Ice Cream” by Sellami, Vemu, & Morris Page 2

L.ii — Quantification of Dairy Intolerance by Region 3. Count the black and white dots for each circled region and calculate the percentage of dairy tolerant people in each region. Plot your findings in the graph below. (5) % Dairy Tolerant Individuals by Region of Origin 4. What does this data mean in terms of likelihood for a person from a particular geographic area to be dairy wleran For mMstance, woatd Know r“‘j Someone Came tvom a. Parh calar Sc_osn-ph‘-c. area Nelp we predid-if They would be lactuse perss svendf () “I Scream for Ice Cream” by Sellami, Vemu, & Morris Page 3

Part Il — Lactase Catalyzes the Hydrolysis of Lactose ILi — 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: Tve never taken Lactaid. Whar is it? 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. Chris: 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? Sanjeet: 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 CH,OH C!JHQOH CH,OH K OH Glucose (¢ oH < Lactase OH\—0 O HO 1 OH OH (enzyme) e CH,OH OH Galactose 9 —0 oM 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. Questions 1. What is the difference between a protein and an enzyme? Search the internet if you need more clarification and write down a definition of each term. ( > “I Scream for Ice Cream” by Sellami, Vemu, & Morris Page 4

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