Introduction
We’ve learned that DNA is the genetic material that organisms inherit from their parents, but have you ever thought about what exactly this DNA encodes for? How do our cells use DNA as a set of instructions for life? How is the information in our DNA/genes used by our bodies? And what happens when the DNA is mutated or not used properly?
Materials
DNA sequence
Computer with an internet connection
Procedure
Obtain your DNA sequence from your teacher. It will be emailed to you at the beginning of the week.
Convert your DNA sequence into a complementary mRNA sequence.
EXAMPLE: DNA: T A C G G C T A G
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Determine the codons.
EXAMPLE: mRNA: A U G C C G A U C
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Codons: AUG CCG AUC
Codons:
Translate the codon sequence into an amino sequence. Use the chart provided.
Codons: AUG CCG AUC
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Amino Acids: Methionine Proline Isoleucine
Amino Acid Sequence:
5. Write out the one-letter abbreviations for the amino acids in the sequence. Use the chart provided.
6. Go to http://www.ncbi.nlm.nih.gov/BLAST/ and choose Protein-Protein BLAST (top of the second column).
7. Enter the one-letter abbreviations for your amino acid sequence in the SEARCH box – be sure to enter them in the correct order!
8. Click on the “BLAST” button.
9. At the next page, click on the “FORMAT” button. It may take a few minutes to process your sequence.
10. At the next page, scroll down to the list of proteins that matched your sequence. Choose one that matches one on the list of possible proteins that was given to you.
11. The protein our DNA sequence encodes is (should be in the list provided): ___Leptin______
12. Now search www.google.com with the name of your protein to find out the disease your protein is involved in.
12. This protein is involved in the following disease: ____________Obesity__________
13. Write a brief paragraph on the next page explaining the disease caused by this protein or a mutation in this protein.
Leptin
Leptin is a hormone produced by fat cells, that can have an effect on energy balance, (Klok, Jakobsdottir & Drent, 2007). Energy balance is required to maintain a stable body weight. It works in conjunction with ghrelin, which has an effect on meal initiation. Leptin is used to suppress one’s food intake, which can result in weight loss. When there is an abnormality in the production and release of leptin, it can result in obesity. This occurs when the amount of the hormone is increased (Klok et al, 2007). At the same time, the amount of ghrelin appears to decrease, also contributing to obesity. Leptin is released into our circulatory system via adipose tissue and leptin levels are correlated with BMI, (Klok et al., 2007). It sends signals to the brain, indicating whether or not there is a need for food intake and/or an increase in energy expenditure. Long-term over eating leads to an abundance of leptin expression, which then leads to more over eating. Montague et al., as cited in Klok et al., showed that leptin deficiency at birth, from a frameshift mutation, was associated with normal birth weight, but was then followed by rapid development of severe obesity because of over eating and the inability to feel satisfied. Other results however, have shown that the increase in leptin could be a result of obesity and not the other way around. Some researchers think that obese people are simply leptin resistant (Klok et al., 2007). This likely results from a period of over eating, which causes the leptin system to become so disrupted that it leads to defects. Then, the hypothalamus becomes less sensitive to leptin which leads to an increase in its levels (Klok et al., 2007)
References
Klok, M. D., Jakobsdottir, S., & Drent, M. L. (2007). The role of leptin and ghrelin in the regulation of food intake and body weight in humans: a review. Obesity Reviews, 21-34.
