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17.1 Genes specify proteinsA. Garrod (1902)

1. 1st to suggest that genes determine phenotypesB. Beadle & Tatum Experiment - 1940

1. Proposed: each gene specifies the synthesis of 1 enzyme. 2. Called: the 1 gene to 1 enzyme hypothesis.

C. Ongoing research caused revision to 1 gene to 1 enzyme hypothesis1. Apply to polypeptides that are not enzymes2. 1 gene = 1 polypeptide hypothesis

https://www.dnalc.org/view/16360­Animation­16­One­gene­makes­one­protein­.html

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D. Overview of Transcription & Translation (The Central Dogma)

primary transcript

- No pre-mRNA = no RNA processing

1. Proposed by Francis Cricka. The flow of genetic information is from DNA to RNA to

protein. b. A gene is a continuous linear sequence of DNA that codes

for one protein.c. Genes are fixed in location on chromosomes.

2. Crick hypothesized the existence of mRNA before it was discovered

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3. Exceptions to Central Dogma:a. Retroviruses reverse the flow of genetic information using reverse transcriptase

RNA→ →copy DNA→ host DNA → mRNA →protein

b. Genes can edit themselves at the DNA level (Susumu Tonegawa and antibody genes) and mRNA level (exons/introns)

c. Transposons can move about on chromosomes and act as “controlling elements” to regulate transcription (Barbara McClintock)

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E. Triplet Code

1. Flow of info from gene to protein based on triplet code called codons

2. Each codon determines the amino acid that will be added to the protein

3. It is redundant

a. more than 1 codon can determine the same amino acid

4. Not ambiguous

a. No codon determines more than 1 amino acid

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The Genetic Code