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BIO 2400 (24)
Lecture 13

BIO 2400 Lecture 13: Ch. 13

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BIO 2400
Annkatrin Rose

Ch. 13 • Genetic Bases for Protein Synthesis o Structural genes ▪ Transcribed into messager RNA ▪ Translated into polypeptides (proteins) o Main function of genetic material is to encode the production of cellular proteins ▪ In the correct cell ▪ At the proper time ▪ In suitable amounts • Genes Produce Proteins o Archibald Garrod proposed this idea o Based on studies of alkaptonuria ▪ “Black urine disease” ▪ Due to missing enzyme • Beadle and Tatum’s Experiment o Tested whether each gene produces one enzyme or many enzymes o Genetic model: ▪ A common bread mold o Experimental Set Up ▪ Irradiate to produce mutations ▪ Identify strains that cannot grow on medium • Growth can be restored by adding only one vitamin o Conclusion ▪ Only one enzyme defective ▪ Each gene only coded for ONE enzyme ▪ One gene- one enzyme theory o Caveats/modifications ▪ Enzymes are only one category of proteins ▪ Some proteins are composed of two or more different polypeptides • Polypeptide= amino acid chain (STRUCTURE) • Protein= functional enzyme (FUNCTION) • Review of PROTEINS o Made from amino acids o Peptide bones link amino acids o Chains of amino acids form polypeptides o Polypeptides fold into proteins ▪ 3d shape determines functions o 20 amino acids found in polypeptides ▪ nonpolar amino acids are hydrophobic ▪ polar and charged amino acids are hydrophilic • more likely on surface of proteins • From Genes to Proteins o Translation ▪ Nucleotide language (mRNA) is translated into amino acid language (proteins) ▪ Based on groups of nucleotides known as condon  How many nucleotides do we need per codon to code for 20 different amino acids? THREE • Coding Problem o How many nucleotides are required to code for a single amino acid in a peptide? ▪ 4 nucleotides – 20 amino acids ▪ If 1 nucleotide coded for one amino acid, proteins could have 4 amino acids ▪ If 2 nucleotides coded for one amino acid, proteins could have 4 = 16 amino acids ▪ If 3 nucleotides coded for one amino acids, proteins could have 4 = 64 amino acids • Experiment 13A o Used a cell free translation system that was developed earlier by other groups ▪ Added synthetic RNA ▪ Added radiolabeled amino acids (probably Nitrogen) o Used polynucleotide phosphorylase to make RNA ▪ Does not use a template  random sequence ▪ Ex. 70% G and 30% U are mixed together then… *product rule o Hypothesis ▪ Sequence of bases in RNA determines the incorporation of specific amino acids in the polypeptide • Goal: decipher the relationship between base composition and particular amino acids • The Genetic Code o Degeneracy of the code ▪ 3rd position in codon flexible ▪ START (INITIATION CODON) CODON: AUG • Exception: mitochondria ▪ Synonymous codons… STOP
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