Lactase Persistence I Scream For Ice Cream 2024
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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
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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
2. What is 2 monosaccharide and what is a disaccharide? Which of these three sugars are mono or disaccharide? Look this up on the internet and label the figure above (Figure 2) with the corresponding terms. (3) (2) 3. How can taking Lactaid help someone who is lactose intolerant to digest lactose? 4. Why would a test for tolerance to lactose measure the levels of blood glucose and not lactose? (_J ) 5. Would you expect higher or lower glucose levels for dairy tolerant individuals after consuming milk? Why? y( 5 ) Draw your predictions for a lactose tolerant and lactose intolerant person into the graph below and explain wh Blood Glucose after Drinking Milk “I Scream for Ice Cream™ by Sellami, Vemu, & Morris Page s
IL.ii — Blood Glucose Test Esiankifki: Xiao-Ma: Sanjeet: Chris: Esiankiki: Here are the results that the group of friends obtained from —— Blood glucose (ma/dL) Esiankiki’s mother. Each of them had to drink a liquid that drinkingmilk: | 0 | 30 | 60 | 9 | 120 contains lactose. At the time the liquid was consumed, a Bjom 17 | 128 | 136 | 160 | 152 physician assistant took a blood glucose measurement and Chils 57 | w1 | 135 | 1=4 | 14 repeated this every 30 minutes for two hours. oo dia % | & | @ ! ol | & Questions Esiankiki | 108 | 116 | 129 | 141 | 139 6. Plot the results from the five individuals in the graph below. Linde 8¢ | 168 | %8 | 143 | WO Make sure to include a legend for your graph. The physician Sanjeet 97 | 96 | 94 | 83 | 88 Oh, now I remember—I've heard of this test before. My mom’s a physician with her own office here in town. I know that my mom is participating in a clinical trial for a new lactose intolerance test that measures blood glucose. Now I wonder if 'm lactose intolerant. [ once had really bad stomach aches when I ate ice cream. Maybe that’s why? If we go to her office, we could try to participate in the trial and if we ask nicely, she might give us the data. Wouldn' it be nice to know for sure if you are lactose intolerant? Yes, I would love that! And you know what’s interesting—when I was a baby, I didn’t have these issues but I was able to digest milk just fine as I was breastfed. Wow that’s fascinating—so as a baby you probably did produce the lactase enzyme and, if you are right, then your body at some point just stopped making it. Suddenly biology is starting to be more interesting... Well, that would explain why my mom calls people who can eat dairy without problems “lactase persistent.” I never really understood what she meant by that. She probably means that the production of lactase enzyme persists in those individuals when they are adults. Let’s go and do that blood test; I'm really curious now. assistant has already plotted one individual’s dara. {mg/di) BED SR Ol Blood Glucose after Drinking Milk : Y Y &y & 88 time (minutes) “I Scream for Ice Cream” by Sellami, Vemu, & Morris Page 6
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7. Can you divide the group of individuals into two groups based on this data? If so, explain according to which (2) observation you would group individuals and who would belong into each group: A: B: 8. According to this data and your grouping, who of the groups are probably lactase persistent individuals? (2') 9. Does the data from the blood glucose measurement match what you had heard from the individuals during @.\ their conversation on being able to eat ice-cream? 10. How do you think the graph would look like if Sanjeet had taken the test as a baby? (Q') 11. A person taking this test is usually asked to fast prior to taking the test. Why do you think that is? L&-‘ “I Scream for Ice Cream” by Sellami, Vemu, & Morris Page 7
— 3 hhmi Biolnteractive PROCEDURE There are several ways to test whether someone is lactase persistent or nonpersistent. One method, the blood glucose test, is shown in the short film Got Lactase? The Co-evolution of Genes and Culture. Table 1 shows the blood glucose levels of the film’s narrator, Spencer Wells, and six other individuals over time. The glucose levels were measured using glucose strips and a glucose reader similar to the one in the film. After baseline levels (i.e., the ones at “0 minutes”) were measured, each person drank a liter of milk. Their blood glucose levels were measured again at 15, 30, 45, and 60 minutes after drinking the milk. . Movie 1S \inked on Canvas ) Table 1. Blood glucose test results for seven adults tested in Sarah Tishkoff's laboratory. Blood Glucose (mg/dL) Individual 0 minutes 15 minutes 30 minutes 45 minutes 60 minutes Spencer Wells 117 128 146 160 152 Peter 97 111 135 154 143 Rachel 96 99 | 105 101 98 Katherine 95 97 99 101 102 Sarah 108 116 129 141 139 Michael 94 109 128 143 140 Arthur 97 96 94 83 88 1. Plot the data in Table 1 on the graph below, which already includes the results for Spencer Wells. Add more entries to the legend as needed. Blood Glucose Test Results 160 150 140 = Spencer Wells 130 120 110 - Blood Glucose (mg/dL) 100 90 80 S . . . L - 0 10 20 30 40 50 60 Time (minutes) Enzymes & Reactions dpdated January 2020 wwiw.Biolnteractive.org Page2oid
hhmi Biolnteractive After graphing the data, answer the following questions. 2. Why might someone’s blood glucose levels after drinking milk indicate their lactase activity? Ll) 3. Divide the individuals in Table 1 into two groups (A and B) based on their blood glucose test results. Write the names of the individuals in each group, including Spencer Wells, below. Ll) Group A: Group B: 4. Explain your rationale for dividing the individuals into these two groups. Use data from your graph to (Z') support your answer. 5. Based on these data, do you think the individuals in Group A are lactase persistent or nonpersistent? Cl) Describe the evidence that supports your answer. 6. Based on these data, do you think the individuals in Group B are lactase persistent or nonpersistent? ( ‘) Describe the evidence that supports your answer. 7. If the blood glucose test was performed on people from the Maasai population in Kenya, would their results (Z) be more like those of the individuals in Group A or Group B? Explain your prediction. (Hint: As discussed in the film Got Lactase? The Co-evolution of Genes and Culture, the Maasai traditionally raise cows for food.) Enzymes & Reactions Updated january 2820 www.Biolnteractive.org Page 301 b
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hhmi Biolnteractive e EXTENSION: The Hydrogen Breath Test Another common way to test whether a person is lactase persistent or nonpersistent is the hydrogen breath test. This test uses the amount of hydrogen in a person’s breath to check for lactose fermentation. As described in the “Background” section, undigested lactose is fermented by bacteria in the large intestine. Fermentation produces several gases, including hydrogen, that can exit the body through the anus. These gases can also be absorbed into the blood, circulated to the lungs, and eliminated through the breath. With lactase e -.rJ;a ctasféb ~ Lactose Glucose + Galactose Small intestine Without lactase — . Lactose . lactose e ] s | Fermentation w Acids g Small intestine Large intestine Figure 2. A diagram comparing what happens to lactose in the intestines of individuals with and without the lactase enzyme, Table 2 shows the levels of hydrogen in the breath of four adults tested for lactase persistence. As in Table 1, the measurements at “0 minutes” represent baseline levels before drinking milk. The other measurements were taken at various times after drinking milk. Table 2. Hydrogen test results for four adults. Hydrogen Breath Levels (ppm) Individual 0 minutes 30 minutes 60 minutes 90 minutes 120 minutes Lisa 5 6 9 8 5 Dan 4 9 8 29 35 Cindy 6 8 10 31 32 Brian 4 7 6 9 6 Enzymes & Reactions Updated January 2020 www.Biolnteractive.org Page 4 of §
g hhmi Biolnteractive 1. Create your own irgh of the data in Table 2. Your graph should include a title, labels for the x- and y-axes, and a legend. ) After graphing the data, answer the following questions. 2. Which individuals in Table 2 are likely to be lactase persistent? Use data from your graph to support your answer. (2—) 3. Which individuals in Table 2 are likely to be lactase nonpersistent? Use data from your graph to support your answer. 4. Think of another type of test to determine whether a person is lactase persistent or nonpersistent. Describe your idea in one or two sentences. ¢ 7—) Enzymes & Reactions Updated January 2020 www.Biolnteractive.org Page Sof §