1. The Genetic Code
Miss Richardson
SBI4U

2. A physician at Oxford University, studied the disease alkoptonuria
A build-up of homogentisic acid causes urine to turn black when exposed to air
Garrod collected family and medical data
Deduced that the condition was a recessive disorder caused by a defective enzyme in the metabolic pathway of phenylalanine
Garrod’s work had shown a link between genes and proteins
1902 – Archibald Garrod

3. 1941 - Beadle & Tatum Studied the bread mold Neurospora crassa
Grew cultures on minimal mediums and exposed them to x-rays
This produced some organisms with mutant genes
They crossed the F1 generation with non-iradiated Neurospora
Beadle & Tatum

4. The F2 generation that was produced could only replicate with the addition of the amino acid arginine
They had shown the arginine-dependent strains had lost use of the specific gene facilitating the production of this amino acid
1941 – Beadle & Tatum

6. One Gene-One Polypeptide Hypothesis
Beadle & Tatum concluded that one gene specifies one enzyme
They shared the Nobel prize for the “One gene – One enzyme hypothesis”
The hypothesis has been revised to “One gene – One polypeptide”
One Gene-One Polypeptide Hypothesis

7. Worked on identifying amino acids in insulin and noticed each insulin molecule had the same amino acid sequence
Concluded each protein has a specific amino acid sequence
Suggested that DNA too must have an ordered sequence
1953 – Frederick Sanger

8. Protein synthesis was known to occur in the cytoplasm, yet DNA is only found in the nucleus
1961 – Francois Jacob & Jacques Monod proposed that another nucleic acid, RNA was synthesized by DNA of genes
messenger RNA (mRNA) would be a complement of the DNA sequence, providing the amino acid sequence required for the specific protein
Messenger RNA

9. The mRNA Hypothesis
Working with Sydney Brenner & Mathew Meselson, Jacob & Monod confirmed their hypothesis

10. 1961 – Through work with E. coli and bacteriophages, Crick & Brenner demonstrated that the genetic code is read continuously in triplets, or codons
Research groups worked for four years to determine the codons specific to each amino acid
The Genetic Code

11. AUG = START codon
UAA, UAG & UGA = STOP codons
The Genetic Code

12. It is redundant – more than one codon can code for the same amino acid
It is continuous – it reads codons without spaces or overlap
It is nearly universal – all organisms build proteins with the same genetic code
The Genetic Code