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From Gene to Protein—Transcription and Translation
By Dr. Ingrid Waldron and Dr. Jennifer Doherty, Department of Biology, University of Pennsylvania, Copyright, 2011[1]

In this activity you will learn how the genes in our DNA influence our characteristics. For example, how can a gene result in very pale skin and hair? How can another gene cause sickle cell anemia?

Basically, a gene provides the instructions for making a protein and proteins influence our characteristics. For example, most of us have a protein enzyme that can synthesize melanin, the main pigment that gives color to our skin and hair. In contrast, albino people make a defective version of this protein enzyme, so they are unable to make melanin and they have very pale skin and hair.

How the Gene for Sickle Cell Hemoglobin Results in Sickle Cell Anemia

Different versions of the same gene are called different alleles. These different alleles share the same general sequence of nucleotides, but they differ in at least one nucleotide in the sequence.

Different alleles can result in different characteristics as follows: differences in the nucleotide sequence in the gene
result in differences in the nucleotide sequence in mRNA result in differences in the amino acid sequence in the protein result in differences in the structure and function of the protein result in differences in a person's characteristics.

For example, if a person has an allele that codes for a normal version of an enzyme to make melanin, this person will have normal skin and hair pigmentation. In contrast, if a person’s alleles code for a defective version of this enzyme, this person’s cells will not be able to make melanin, so this person will have albinism.

In this section, you will learn about another example: normal vs. sickle cell hemoglobin. You will work with your partner to understand how differences between the normal and sickle cell hemoglobin alleles result in different hemoglobin proteins. Then you will learn how the differences between the normal and sickle cell hemoglobin proteins can result in good health or sickle cell anemia.

1. In the table below, compare the DNA for the Beginning of the Normal Hemoglobin Gene vs. the Beginning of the Sickle Cell Hemoglobin Gene. What is the only difference?

2. Complete the table. (Use the table on page 5 to help with translation.)

|Beginning of Normal Hemoglobin Gene | CACGTAGACTGAGGACTC | |Transcription produces: |codon 1 |codon 2 |codon 3 |codon 4 |codon 5 |codon 6 | |Beginning of Normal Hemoglobin mRNA |GUG |CAU |CUG |ACU |CCU |GAG | |Translation produces: |amino acid 1 |amino acid 2 |amino acid 3 |amino acid 4 |amino acid 5 |amino acid 6 | |Beginning of Normal Hemoglobin Protein |Valine |Histidine |Leucine |Threonine |Proline |Glutamic acid| | | |Beginning of Sickle Cell Hemoglobin Gene | CACGTAGACTGAGGACAC | |Transcription produces: |codon 1 |codon 2 |Codon 3 |codon 4 |codon 5 |codon 6 | |Beginning of Sickle Cell Hemoglobin mRNA |GUG |CAU |CUG |ACU |CCU...
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