1 1)Beadle & Tatum’s Experiment - Using bread mold neurospora to show each gene encodes the structure of one polypeptide. 2)Meselson & Stahl’s Experiment - Using the radioisotope labeling technique to show the semi- conservative model of DNA replication
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1)Beadle & Tatum’s Experiment
- Using bread mold neurospora to show each gene encodes the structure of one polypeptide.
2)Meselson & Stahl’s Experiment
- Using the radioisotope labeling technique to show the semi-conservative model of DNA replication
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4.1.3 Gene concept; one gene one polypeptide
• George Beadle and Edward Tatum
experiment: connection between genes & metabolism.
• Neurospora crassa as experimental organism.
- short life-cycle, easily grown.
• Since it is haploid for much of its life cycle, mutations would be
Neurospora crassa able to synthesize all of the amino acids and other
chemicals needed for growth
mutations will affect a single genes and single enzymes in specific metabolic pathways.
Gene concept; one gene one polypeptide
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Chemical reactions occurring in the body mediated by enzymes
(proteins)
Heritable traits- must be a relationship between the gene and proteins.
• Beadle and Tatum proposed the "one gene one enzyme" theory.
Gene concept; one gene one polypeptide
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One gene, one polypeptide• One gene codes for one protein.
• "One gene one enzyme" modified to "one gene one polypeptide" since many
proteins made of more than one polypeptide
• Biosynthesis of amino acids: complex chemical reactions mediated by enzymes,
which if mutated- shut down the pathway
• no growth.
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4.2 DNA Replication
Watson and Crick Model of DNA suggest that each strand of DNA molecule could serve as a template, for the synthesis of the opposite strand.
Each half-helix could pair with their complementary nucleotides to replace its missing partner.
The result would be two DNA double helices, each identical to the original.
Definition :Process of copying a double stranded DNA strand which is the two resulting double strands are identical and each of them consist of one original and one newly synthesize strand.
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3 hypothesis that told about DNA replication :-
CONSERVATIVEboth parent (or old) strand remain together and an all new copy is made
SEMICONSERVATIVE the 2 strand of the parental molecule
separate and each functions as a template for synthesis of a new complementary strand
DISPERSIVEeach strand of both daughter molecules contains a mixture of old and newly synthesized parts
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In 1958, Meselson and Stahl studied the replication of E.Coli .
Meselson and Stahl Experiment
Hypothesis : DNA replication are take place by
semiconservative mechanism
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Conclusion Hypothesis are accepted. Experiment approved that DNA