Archibald Garrod - noted prevalence of diseases in certain families 

• alkaptonuria - lack of enzyme leads to formation of alkapton (homogentisic acid) in urine
• believed that inherited diseases may be due to enzyme deficiencies

Beadle/Tatum - found that genes specify enzymes  

• deliberately created mutations in chromosomes
• used X-rays to damage DNA in some yeast spores
• placed yeast in minimum medium (only contained sugar, ammonia, salts, water, vitamins)
  • those that couldn’t make growth compounds would die
  • material added to minimum medium to see what the yeast cells w/ damaged DNA lacked
• found that every enzyme had a different chromosomal site
• one-gene/one-enzyme hypothesis - genes produce effects by encoding for enzymes (aka one-gene/one-polypeptide hypothesis)

Frederick Sanger - found complete amino acid sequence for insulin 

• 1st sequence to be determined for a protein
• showed that all proteins were just strings of amino acids in a certain order

Vernon Ingram - found molecular basis for sickle cell anemia 

• found that change from glutamic acid to valine in the protein caused sickle cell anemia
• gene - sequence of nucleotides that determines the amino acid sequence of a protein
• some genes used to make special RNA forms