The Role of DNA Chapter 9 Section 2 Part 1

OBjectives Know and understand the evidence that DNA codes for proteins

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

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

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!

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

What happens? Phenylpyruvate builds up in the body Causes intellectual disability, heart disease, death if untreated Occurrence is about 1 in 15 000 births About 2% of US population carries the gene (heterozygous) Heterozygous individual can usually make normal enzymes

Genes code for Proteins! Read pages 237-238