 British physician from the 20 th century  Studied patients with alkaptonuria › A genetic disorder which causes black urine, containing alkapton  Garrod’s Hypothesis: › one gene directs the production of one enzyme › A defective enzyme causes an “inborn error of metabolism” which results in the inability to break down alkapton › Enzymes are controlled by heretic material  An error in heretic material meant an error in an enzyme

 Represented the relationship explain by Garrod through experiments on red bread mould, Neurospora crassa  One strand of the mould was able to synthesize all the amino acids and vitamins it needed for optimum growth, given minimum nutrients  Mutant strains were created using X-rays and UV lighting and were not able to replicate with minimum nutrients  4 mutant strains were discovered, each had a different defective gene  Beadle and Tatum concluded that one gene acts by directing the production of only one enzyme  Their hypothesis is known as the one gene-one polypeptide hypothesis

 Studied the amino acid sequence of hemoglobin from individuals with sickle cell anemia  Discovered a base switch in one of the polypeptides  The switch caused a change in the structure of the red blood cell  Ingram’s research showed that a gene specifies the kind and location of amino acids in polypeptide chains  Ingram linked heretidy abnormality to a single alteration in the amino acid sequence of a protein

 Genes are expressed in the phenotype of an individual  Two parts: Transcription & Translation  Moves in one direction: gene  protein  More than one protein is made per gene, therefore multiple copies must be made  The desired template sequence of DNA is copied (transcription) then made into a polypeptide chain (translation)  DNA  RNA  Protein

 Contains a ribose sugar (remember: DNA has a deoxyribose sugar)  Contains Uracile, which pairs with Adenine, instead of Thyamine  RNA is only ever in single-stranded form  There are 3 kinds of RNA 1. mRNA: messenger RNA 2. tRNA: transfer RNA 3. rRNA: ribosomal RNA

1. mRNA › Sequence of base pairs transcribed from DNA 2. tRNA › Transfers the appropriate amino acids to the ribosome to build proteins 3. rRNA › A structural component that forms a ribosome

1. Initiation › RNA polymerase binds to promoter region 2. Elongation › Building of mRNA by adding RNA nucleotides 3. Termination › The mRNA is finished when stop signal is reached 1. Initiation › Ribosome recognises mRNA 2. Elongation › Amino acids are strung together 3. Termination › Stop codon is reached, polypeptide chain is released

 Nucleotides are grouped in threes  Each triplet is called a codon  Four bases, in triplets give us 4 3 = 64 possible combinations  Each codon codes for 1/20 amino acids  Since there are 20 amino acids and 64 possible codons, multiple codons code for the same amino acids  AUG is the start codon, whereas UAA, UAG, and UGA are stop codons