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.
The two strands of DNA encode the same information in complementary form suggesting a method of replication.
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.
Thus gene --> enzyme.
Mendelian Inheritance Alkaptonurea
One gene -> one enzyme.
One gene -> one protein.
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.
RNA can form complementary strands with the template DNA
RNA polymerase transcribe one strand of DNA to 5' to 3' RNA copy
That transcript move out of the nucleus into cytoplasm.
-RNA vs. DNA
Amino acid sequence of human insulin protein
DNA has a sequence.
Proteins have sequences.
One gene -> one protein.
One nucleotide per amino acid -> 41=4 amino acids.
Two nucleotides per amino acid -> 42=42 16 amino acids.
Three nucleotides per amino acid -> 43=64 amino acids.
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:
Gobind Khorana: for a triplet code(=codon) there will be three "reading frames" AAGAAGAAGAAG could be read as AAG /
AGA / GAA -> Lys / Arg / Glu
The code is degenerate
The decoding problem:
DENT LECTURE 6: Breaking the Genetic Code
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