november 13 notes

November 13, 2009—- notes

Review of last class
1) Complementary interactions between shine-dalgarno sequence and rRNA—ribosome binding to mRNA
2) Ribosome moves down mRNA until reaches AUG, then brings in first tRNA (attached to Methionine)
3) Ribosome keeps moving down mRNA, bringing in tRNAs whose anticodons match mRNA codons, tRNAs have amino acids attached
4) At stop codon, Release Factors bind with ribosome, mRNA stop codon, RFs detach ribosome from mRNA, amino acid chain from ribosome
New materials
a) Polyribosomes: one mRNA with lots of ribosomes attached to it, in different stages of translating mRNA
1) Kinds of mutations
a) Point mutations: a change in the DNA sequence that only changes one base
• Mutation: any change in the DNA sequence of an organism (not a change in gene expression)
• Missense mutation: changes to DNA sequence that leads to a change to amino acid sequence of protein
• Nonsense mutation: change to DNA so there’s now an early stop codon in the mRNA, so short protein
• Silent mutation: change in the DNA sequence, but it results in no change to the amino acid sequence of the protein
b) frameshift mutation:addition or deletion of 1or2 bases

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