Concept explainers
Health Watch Lack of an Enzyme Leads to Lactose Intolerance
If you enjoy ice cream and pizza, it might be hard for you to imagine life without these treats. However, such dairy containing treats cannot be enjoyed by much of the world’s population. Although al young children normally produce lactase (the enzyme that breaks down lactose, or “milk sugar”), about 65% of people worldwide, including 30 to 50 million people In the United States, produce less of this enzyme as they progress through childhood, a condition called lactose intolerance. In the worst cases, people may experience abdominal pain, flatulence, nausea, and diarrhea after consuming milk products (FIG. E6-2).
Why do people stop synthesizing the enzyme for this nutritious food? From an evolutionary perspective, it makes sense not to continue expending energy to produce an enzyme that has no function. In our early ancestors (who had not yet domesticated livestock), lactase lost its function in very early childhood because, after weaning, these people no longer had access to milk—the main source of lactose. As a result, many modern adults cannot digest lactose because the gene that encodes lactase is regulated by being turned off after weaning. Lactose intolerance is particularly prevalent In people of East Asian, West African, and Native American descent. Genetic studies have revealed that between 10.000 and 6.000 years ago. some people in northern Europe and the Middle East acquired mutations that allowed them to digest lactose throughout their lives. These mutations were advantageous and gradually spread because they provided better nutrition for members of agricultural societies, who could obtain milk as well as meat from their livestock. Their descendants today continue to enjoy milk, ice cream, and extra-cheese pizzas.
FIGURE E6-2 Risky behaviour? For the majority of the world’s adults, drinking milk invites unpleasant consequences.
EVALUATE THIS A family brings their 8-year-old adopted child to a pediatric clinic because she has begun to suffer from diarrhea and stomach cramps after drinking milk. What would the pediatrician suspect was the cause? If tests confirm his suspicions, what approaches would he recommend to deal with the issue? Are there dairy products that would not cause the reaction? How might they work?
Want to see the full answer?
Check out a sample textbook solutionChapter 6 Solutions
Biology
- People with lactose intolerance cannot digest the common dairy sugar lactose. Besides being careful not to eat dairy foods, is there anything else a lactose-intolerant person can do?arrow_forwardMany people suffer from lactose intolerance. Outline how food products containing milk may be made ‘lactose free’, and thus helping to avoid triggering the condition.arrow_forwardPhosphorylase b Phosphorylase a Active site 1. Glycogen phosphorylase is the regulatory enzyme in glycogen degradation. Using the diagram, differentiate the 4 different forms noting which would be the most active and the least active, and state under what 2 ATP 2 ADP R state conditions each would be the dominant form. 2 ATP 2 ADP T state 100-0arrow_forward
- Some amino acids are both glucogenic and ketogenic. Explain the difference between the two types and why some amino acids can be both.arrow_forward. A patient rushed into a hospital complaining of severe pain and a burning sensation in his chest region. Doctors suspected it to be a case of gastric ulcer or a myocardial infarction. Hence, they immediately screened his blood serum for marker enzyme levels, where they found elevated levels of the LDH, (H4) isoform. Analyse the clinical condition of the patient.arrow_forwardThe sweet taste of freshly picked corn (maize) is dueto the high level of sugar in the kernels. Store-bought corn (several days after picking) is not as sweet, because about 50% of the free sugar is converted to starch within one day of picking. To preserve the sweetness of fresh corn, the husked ears can be immersed in boiling water for a few minutes (“blanched”), then cooled in cold water. Corn processed in this way and stored in a freezer maintains its sweetness. What is the biochemical basis for this procedure?arrow_forward
- Account for the occurrence of lactose intolerance? Account for the distinct advantages of human milk over formula or cow’s milk for infants. Briefly discuss the importance of protein in our bodies? What are the major sources of protein?arrow_forwardFozyme Action: An Investigation of Lactase Activity 137 PART F EFFECT OF pH ON ENZYME ACTIVITY Activity of Lactaid at Several pls Observation with Tes Tape" Glucose present? Lactose 90 change More Grean tello Green Hellow NO change Green NO pH 7 Yes, 100 mgloL pH 2 Yes 7100 mglaL pH 10 NO Glucose tes 300 mglaL RART G. EFFECT OF AN INHIBITOR ON ENZYME ACTIVITY Inhibitor Effects Observation with Tes Tape Glucose present? Light Green Teal Yellow IGreen Dark Brown Lactose Yes Lactaid" NO Ethanol Yes Yes Glucose 1. What is the optimum pH of the lactose-conversion reaction, as shown by your data? 2 Did ethanol act as an efficient inhibitor of the lactose conversion to glucose and galactose? 3. Summarize your findings about the concentration, temperature, and pH sensititivity of lactase.arrow_forwardY ANTIBODIES DIETARY B12 PERNICIOUS ANAEMIA HYDROXYCOBALAMIN 5. Pernicious anemia is a disease in which the intestine is unable to absorb vitamin B12, frequently due to the loss of the generically named "intrinsic factor" produced by the parietal cells of the stomach lining. Intrinsic factor is a glycoprotein that binds to vitamin B₁2 and is required for its uptake in the ilium. Vitamin B12 is synthesized only by microbes, and we get it either from digesting animal protein or from our commensal microbiome. Vitamin B₁ is unique among metabolic cofactors in that it contains the trace element cobalt, coordinated in a corrin ring structure that is similar to the porphyrin ring system in heme. Loss of intrinsic factor, often through autoimmunity, results in the inability to absorb B12 and ultimately a loss of red blood cells that results in anemia and can be deadly ("pernicious"). ILEUM NUMBNESS (a) In pernicious anemia, N 5-methyltetrahydrofolate accumulates, and cells run out of…arrow_forward
- . In the biosynthesis of amino acids. Glutamate can serve as an intermediate in the synthesis of the following amino acids all but one; O Serine O Aspartate Alanine O Histidinearrow_forwardFates of glucose 6 phosphate. Fill in the missing info for the overview of metabolismarrow_forwardIn class, I mentioned that fructose is metabolized differently in the liver compared to glucose. Refer to the figure shown below to calculate the number ofATPs you would expect from the metabolism of fructose in the liver. Show your work! Fructokinase Fructose Fructose-1-P АТР ADP Aldolase B Dihydroxy- acetone phosphate Glyceraldehyde АТР Triose kinase Triose phosphate isomerase ADP 4 - Glyceraldehyde-3-P Glycolysis Руruvate Acetyl-CoA Fatty acids and triglyceridesarrow_forward
- BiochemistryBiochemistryISBN:9781305577206Author:Reginald H. Garrett, Charles M. GrishamPublisher:Cengage LearningBiology: The Unity and Diversity of Life (MindTap...BiologyISBN:9781305073951Author:Cecie Starr, Ralph Taggart, Christine Evers, Lisa StarrPublisher:Cengage Learning