Understanding the Functions of Proteins and DNA
Ingrid Waldron, Biology Department, University of Pennsylvania, 2012
These key concepts and activities are suggested as part of an introductory unit on biological molecules (or as an introduction to a unit on molecular biology). The overarching goal is to help students understand that proteins and DNA are not just abstract concepts in biology textbooks but rather crucial components of our bodies that affect familiar functions and characteristics.
Proteins are responsible for many important aspects of cell structure and function. •
Differences in the structure and function of proteins result in differences in the characteristics of biological organisms.
1. Brainstorming session using the probe "What are proteins? Why are proteins important?"
2. Show YouTube video "Protein Functions in the Body"
-- omit hormone section which has inaccuracies
-- ask students to identify 5 functions of proteins
3. Hands-on activity: Enzymes Help Us Digest Food (available at http://serendip.brynmawr.edu/sci_edu/waldron/#enzymes) Experiments using the enzyme lactase and discussion questions help students to learn about enzyme function, enzyme specificity, and the molecular basis of lactose intolerance. Students also learn about the scientific method by interpreting evidence to test hypotheses and designing the second and third experiments to answer specific scientific questions about lactase.
4. Review protein functions and reinforce the idea that, if a protein is missing or defective, this has observable effects on our bodies:
Effect if This Protein Missing or Defective* Enzyme
Lactase (breaks down lactose)
Lactose intolerance (difficulty digesting milk)
Enzyme for synthesizing melanin (pigment that gives our skin and hair color)
Albinism (very pale skin and hair) Transport
(protein in red blood cells which transports oxygen in the blood)
Sickle cell anemia
Clotting proteins in blood
Hemophilia (excessive bleeding) *Teacher information on these conditions is provided, beginning on the next page.
DNA contains genes which provide the information necessary to make proteins. •
Different versions of the same gene result in different versions or amounts of a protein, and the differences in the protein result in different characteristics (illustrated in the table above).
1. Discussion of probe question "Why do some people have lactose intolerance, albinism, sickle cell anemia, or hemophilia, and other people don't?"
2. Show "What is a gene?" available at http://learn.genetics.utah.edu/content/begin/tour/ – illustrates both Key Concepts for this section
3. Revisit probe question.
Teacher Information about Conditions Resulting from Missing or Defective Proteins
The alleles for the gene for lactase differ in the nucleotide sequence in the regulatory DNA; this difference influences the rate of transcription of the coding DNA and thus influences the rate of production of the protein, lactase. •
Lactase persistence alleles result in substantial production of lactase throughout life. •
The lactase nonpersistence allele results in substantial production of lactase by infants, but very low levels of lactase in adults, resulting in lactose intolerance.
For virtually all infants and for adults with lactase persistence: -- in the small intestine:
lactase lactose -------- > glucose + galactose
For about two-thirds of adults worldwide:
-- in the small intestine:
low levels of lactase (lactase nonpersistence) -- > most lactose not digested
-- so, in the colon of the large intestine, lactose is fermented by anaerobic bacteria: fermentation
lactose ---------------- > short-chain...
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