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BIOB11H3 Study Guide - Midterm Guide: Positio, Missense Mutation, Chain Termination

Biological Sciences
Course Code
Dan Riggs
Study Guide

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BIOB11-L6,L7: Translation (Protein synthesis)
Association of mRNA w/ ribosomes, and subsequent decoding & formation of a polypeptide chain
Elucidation of the Genetic Code
Information content of DNA/RNA: 4 different nucleotides for DNA or RNA (ATCG or AUCG)
Information content for Proteins: 20 different AAs
Can 1 nucleotide be enough to encode 20 AAs? No, only 41 possibilities available only encode for 4 AAs out of 20 AAs
Can 2 nucleotide be enough to encode 20 AAs? No, only 42 possibilities available only encode for 16 AAs out of 20 AAs
Can 3 nucleotide be enough to encode 20 AAs? Possibly, 43 possibilities available Encode 64, more than enough information in triplet
Decoding the code: Overlapping or non-overlapping?
Can be determined by single base change mutation
Overlapping or Partially overlapping: Single base change mutation will alter MORE THAN ONE AA
Non-overlapping: Only one AA will be altered
Reality: For a single base change mutation, altering only one AA Non-overlapping
Evidence for non-overlapping code: Sickle cell anemia
RBCs became crescent shaped Clog small blood vessels & Lyse easily
- Alters blood vessel diameter; Lower O2 levels cause pain / fatigue
- 1965, Ingram sequences peptides of hemoglobin: Glu to Val substitution by single mutation (GAG to GUG on mRNA) causes Sickle cell
*Altering only ONE AA from the single base mutation
The Consequences of Mutations
Synonymous: Same AA encoded
Non-synonymous: Different AA encoded
Non-sense: Codon now specifies a STOP CODON
Frameshift: Change in reading frame due to insertion or deletion
Insertion or Deletion (Indel) of a single nucleotide
- If occurs in coding sequence Generates a frameshift mutation
Results in a ‘missense’ protein
- 1 or 2 indels Frameshift
- 3 or multiples of 3 Restores reading frame (genetic codes is a triplet code)
Elucidating the code: “a new tool”
In vitro translation system
Lyse cells, centrifuge to remove membranes molecular machinery present, but will it work?
- Addition of radioactive AAs (Radioactive labeled = *)
- Expect: AA* Protein*
- Result: When exogenous RNA is added, Enhanced AA* incorporation into Protein* IT WORKS
Elucidating the code: “an organic chemist”
Organic synthesis of polynucleotides
Nirenberg & Matthaei: Determining what Poly U, Poly A, Poly C encodes for
Putting synthetic mRNA (UUU, AAA, CCC) into bacterial extract
Found that UUU codes for Phenylalanine (F), AAA codes for Lysine (K), CCC codes for Proline (P)
Decoded 3 of the 64 triplets 61 more to go.
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