1. The Role of DNA
Chapter 9 Section 2 Part 1

2. OBjectives
Know and understand the evidence that DNA codes for proteins

3. Proteins
Order of bases in one gene codes for order of amino acids (primary structure)
Amino acids are the basis of formation of a protein
Remember, proteins are produced after H bonding of amino acid chains and specific shapes (secondary and tertiary structure)
Proteins are often used in the cell as enzymes
Different enzymes cause different cells to behave differently

4. Beadle and Tatum George Beadle and Edward Tatum, 1941
Exposed spores of Neurospora crassa (a bread mold) to X-rays or UV radiation and studied the resulting mutations
Each mutant has specific nutrition needs
Discovered that each mutant strain differed by only one gene
Beadle and Tatum were able to create mutants that could not form specific enzymes
Formulated the “one gene one enzyme” hypothesis
Each gene is responsible for building one enzyme

5. One gene, one protein
Linus Pauling separated different forms of hemoglobin (normal and sickled cells)
Discovered that the two forms differ by only one amino acid (out of 300)
Further investigation determined that a gene is responsible for coding for the order of amino acids that make up one polypeptide
Proteins are polymers of polypeptides
One gene, one protein!

6. What happens if the enzyme is wrong?
Phenylketonuria (PKU)
Due to deficiency in one enzyme (phenylalanine hydroxylase)
Correct enzyme converts phenylalanine  tyrosine
Discovered in 1934 by Asbjørn Følling
Gene located on chromosome 12
If gene not present, enzyme lacking, and phenylalanine  toxic phenypyruvate

7. What happens? Phenylpyruvate builds up in the body
Causes intellectual disability, heart disease, death if untreated
Occurrence is about 1 in births
About 2% of US population carries the gene (heterozygous)
Heterozygous individual can usually make normal enzymes

8. Genes code for
Proteins!
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