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GENETIC CODE
Dr. Mahesha H B
Associate Professor and Head
Department of Sericulture
Yuvaraja’s College
University of Mysore, Mysuru, India
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GENETIC CODE
Central Dogma of Molecular Biology
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DNA Amino Acids
General Structure of DNA and Amino Acids showing no specific recognition sites
Hence needs an adaptor molecule i.e., tRNA
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tRNA structure and role in translation
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tRNA acts as an adaptor molecule in translation between DNA amino acids
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Genetic code: The sequence of nucleotides that determines the specific amino acid sequence in the synthesis of proteins.
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Codon: A section of DNA (three nucleotide pairs in length) or RNA (three nucleotide in length) that codes for a single amino acid.
Or
A sequence of three RNA or DNA nucleotides that specifies (codes for) either an amino acid or the termination of translation. termination of translation.
Or
A base sequence corresponding to a particular amino acid is called codon.
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Genetic Code
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Major Properties1. Triplet:Gamow 1954 suggested 3 letter code
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Genetic code is Non-Overlapping,
if it is overlapping three amino acids
Should have been changed in sickle cell
anemia
Non Overlapping
Non Overlapping
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3. Comma less:
Genetic code is comma less
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4.Has Polarity:
Genetic code has polarity i.e., 5’ to 3’ direction.
If it reads in opposite direction it yields a different protein
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5. Universal: Marshal et al., 1967
� In Yeast mitochondria UGA codes for tryptophan, although in the nuclear genes UGA is a termination codon.a termination codon.
� In the ciliate protozoa UAA & UAG codes for glutamine instead of stop signal
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6. Degenerate/Redundant:
Provision or existence of more than one Codon to
perform an activity or function.
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7. Non-ambiguous/unambiguous:
Having or exhibiting no ambiguity or
uncertainty; clear
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Wobble HypothesisCrick – 1966 proposed hypothesis
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Acknowledgementsto
INTERNET
FOR
PICTURES
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