BIOL 112 Lecture Notes - Lecture 6: Phenylalanine, Arginine, Citrulline
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9 Apr 2012
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The sequence of nucleotides is not constrained by the structure. DNA can accommodate any sequence. An arbitrary
sequence can encode information.
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The two strands of DNA encode the same information in complementary form suggesting a method of replication.
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Recall….the key to DNA:
Neither parent affected: 3.1 : 1
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Pee black
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Almost all affected parents give rise to unaffected progeny, therefore not dominant.
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However, in one rare case, where affected father had affected children, 50% children were affected. --> test cross
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Garrod shows that it is a recessive hereditary trait.
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He deduces that it results from the absence of a specific enzyme.
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Thus gene --> enzyme.
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Mendelian Inheritance Alkaptonurea
One gene -> one enzyme.
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One gene -> one protein.
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Beadle and Tatum:
-DNA in nucleus, protein made in the cytoplasm…
-RNA transfers the genetic information from the
nucleus to the cytoplasm where proteins are made.
RNA has an extra hydroxyl group on sugar and Uracil instead of Thymine.
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RNA can form complementary strands with the template DNA
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RNA polymerase transcribe one strand of DNA to 5' to 3' RNA copy
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That transcript move out of the nucleus into cytoplasm.
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-RNA vs. DNA
Amino acid sequence of human insulin protein
DNA has a sequence.
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Proteins have sequences.
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One gene -> one protein.
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One nucleotide per amino acid -> 41=4 amino acids.
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Two nucleotides per amino acid -> 42=42 16 amino acids.
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Three nucleotides per amino acid -> 43=64 amino acids.
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How does the nucleotide sequence of the DNA encode the information that determines the amino acid sequence of a
protien? To encode 20 amino acids with only four nucleotides:
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Gobind Khorana: for a triplet code(=codon) there will be three "reading frames" AAGAAGAAGAAG could be read as AAG /
AGA / GAA -> Lys / Arg / Glu
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The code is degenerate
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The decoding problem:
DENT LECTURE 6: Breaking the Genetic Code
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