The Genetic Code

Goals

  • Explain how the mRNA sequence encodes amino acids
  • Describe what is meant by a reading frame and why it is important
  • Using a codon table, translate a sequence of DNA/RNA into amino acids

Protein Structure on Function

The structure of the protein dictates its function. Thats because most of the functions done in the cell are carried out by proteins. The structure of the protein is a result of folding, and folding is the result of the protein sequence.

Therefore, the way the sequence of the protein affects the folding of the protein, and ultimately effects the function the protein carries out.

How Proteins are Synthesized

Amino acids are linked by peptide bonds which are created by a condensation reaction with water being released. The polarity of the protein has an N-terminal which consists of amino-cation (NH<sub>3</sub><sup>+</sup>), and a C terminal which is a Carboxyl group COO<sup>-</sup>).

A protein sequence is encoded by the ribonucleic acid sequence known as codons are translated. One codon consists of three nucleotides, which will result in one amino acid complementary to the codon being added by complementary base pairing of an anti-codon. See translation for more information.

Credit: https://www.youtube.com/channel/UCCixjRONBE4aaEuTLsH8a2A

Leslie Barnett, Francis Crick, Sydney Brenner Experiment

They knew that there were 20 amino acids. 1 letter code= 4 amino acids, 2 letter codes= 16 amino acids, 3 letter codes = 64 amino acids. They generated mutations with single nucleotide insertions (in one gene)

One mutation disrupted the proteins function, Two mutations disrupted the proteins function, Three mutations did NOT disrupt the proteins function!

There are multiple codons for most amino acids.

AUG (Met) is always the start codon, and there are three stop codons (UAA, UAG, UGA)

The 5′ end of the anticodon is promiscuous (non-selective) for an example, that a U on the anticodon will bind to both an A on the codon at the 3′ end of the codon (5′ end of the anticodon) or a G on the 3′ of the codon (5′ end of the anticodon)

Dictated by the first nucleotide, there are 3 possible “reading frames” which exist for any DNA/RNA sequence