BIO 30_Lec 6_Handout B

Francis Crick and his students established that/the:

• Code for several amino acids
• Genetic code is triplet
• Code is degenerate (one amino acid from more than one codon)
• Code is in tetrads
• An amino acid can only come from one set of codes

Francis Crick and his students established that/the:

• Code is not overlapping
• Base sequence is read from a fixed starting point
• Proposed Wobble hypothesis
• Code is overlapping
• Base sequence can be read at any point without a fixed origin

Wobble hypothesis proposed that

• Precise pairing between 1st and 2nd base of codon and anticodon
• Wobbly pairing at the third position of the base
• No precise pairing among any of the bases
• Precise pairing between 2nd and 3rd base of the codon and anticodon
• Wobbly pairing at the first position of the base

Har Gobind Khorana conducted/deduced

• constructed sythetic mRNA witj different repeating nucleotide combinations (ex. UCUCUC -> serine and leucine)
• Tested via dinucleotide, trinucleotide, and tetranucleotide synthetic mRNA
• final identification of the codons for 20 amino acids
• Degeneracy of amino acid codes

Nature and Characteristics of Genetic Code

• Triplet code
• Continuous and comma free
• non-overlapping and read in successive groups of three nucleotides
• tetrad code
• Overlapps with successive groups of nucleotides

Nature and Characteristics of Genetic Code

• Universal
• Degenerate
• Unambiguous genetic code, rare for one codon to specify more than one amino acid (not the other way around tho)
• Specific depending on the group of organisms

Nature and Characteristics of Genetic Code

• Has Start and Stop signals
• Wobble Occurs in the anticodon
• Wobble does not occur
• Non-specific start and stop signals

Determine the start codons

• AUG (met)
• GUG (val)
• UAG
• UAA
• UGA

Determine the stop codons

• AUG (met)

• GUG (val)

• UAG

• UAA

• UGA