From Gene to Protein:

Chpt. 17

ArchibaldArchibald GarrodGarrod (1909)(1909) hypothesized:hypothesized: “proteins are the “proteins are the

link between genotype link between genotype & phenotype”& phenotype”

How does the DNA lead to specific traits???

1909 - Archibald Garrod

Suggested genes control

enzymes, & enzymes catalyze chemical processes in cells.

Inherited Diseases are “inborn errors of metabolism” where a person can’t make an enzyme.”

ExampleAlkaptonuria (Al ka toe nuria)- where urine turns black after exposure to air b/c of chemical alkapton (Al kae ton).

these individuals must lack an enzyme to metabolize (break down) alkapton (the chemical).

enzyme

enzyme

enzyme

enzyme

GeorgeGeorge BeadleBeadle American(1930)American(1930)

*“ mutations in eye *“ mutations in eye color color (Drosophila)(Drosophila) are are a result of blocks a result of blocks in pigment in pigment production”production”

*“no *“no enzymeenzyme is made is made - therefore pathway - therefore pathway toto produce color produce color pigment is pigment is not not complete… white complete… white eyes”eyes”

QuickTime™ and aTIFF (Uncompressed) decompressor

are needed to see this picture.

G.G. BeadleBeadle & & Edward Edward TatumTatum

Beadle and Tatum set out to provide experimental proof of the connection between

genes and enzymes.

G.G. BeadleBeadle & & Edward Edward TatumTatum

Nobel Prize in Physiology or Medicine 1958

"for their discovery that genes act by regulating definite chemical events"

Cal Tech. Rockefeller Inst. NY, NY

G.G. BeadleBeadle & & Edward Edward TatumTatum

test organismtest organism = = NeurosporaNeurospora

NeurosporaNeurospora

(pink bread mold)(pink bread mold)

G.G. BeadleBeadle & & Edward Edward TatumTatum mutant molds (not wild type) had a

variety of special nutritional needs. Unlike their wild type counterparts, they could not live without the addition of particular vitamins or amino acids to

their food.

G.G. BeadleBeadle & & Edward Edward TatumTatum

*“ various *“ various mutationsmutations must bemust be abnormal variations abnormal variations of genesof genes””

One Gene, One Enzyme One Gene, One Enzyme HypothesisHypothesis

-Beadle & Tatum

wild type mold survived in minimal medium agar.

The wild type mold can produce all of the enzymes it needs to produce the necessary amino

acids to live.

this is the normal metabolic pathway

One Gene, One Enzyme One Gene, One Enzyme HypothesisHypothesis

-Beadle & TatumMutants did not survive in minimal medium

agar.

The mutants must not produce all of the enzymes needed

The enzymes would synthesize particular

amino acids. But they could survive in complete

agar… supplemented with all 20 amino acids.

One Gene, One Enzyme One Gene, One Enzyme HypothesisHypothesis

-Beadle & Tatum

One Gene, One Enzyme One Gene, One Enzyme HypothesisHypothesis

-Beadle & TatumTried to identify where the mutants’ metabolic

defects (mutations) were

One Gene, One Enzyme One Gene, One Enzyme HypothesisHypothesis

-Beadle & TatumAll strains were grown on complete mediacomplete media.

This contained all a.a. & vitamins made by the

wild type, they all thrived…

By the way, this mold By the way, this mold MUST make MUST make ArginineArginine in in order to grow. order to grow.

One Gene, One Enzyme One Gene, One Enzyme HypothesisHypothesis

-Beadle & TatumTook mutants out of the complete media

They did not all They did not all grow when put on grow when put on “minimal media”“minimal media”They figured that mutants They figured that mutants were unable to produce were unable to produce compounds essential for compounds essential for

growth… growth… perhaps their genes did not code for an enzyme… this ultimately did not let

the organism produce arginine??

One Gene, One Enzyme One Gene, One Enzyme HypothesisHypothesis

-Beadle & Tatum

Put each mutant type Put each mutant type in different vials in different vials containing minimal + containing minimal + one amino acid.one amino acid.(in this pix., the a.a. (in this pix., the a.a. is is ornathine)ornathine)

Because Class I grew on Because Class I grew on minimal medium minimal medium supplemented with supplemented with ornithine, citrulline, ornithine, citrulline, or argine, it had to be or argine, it had to be missing missing enzyme Aenzyme A. This . This would be required to would be required to form all three compoundsform all three compounds

One Gene, One Enzyme One Gene, One Enzyme HypothesisHypothesis

-Beadle & Tatum

Class II could not Class II could not produce produce citrulinecitruline, , and that is needed and that is needed for the rest of the for the rest of the pathway to occurpathway to occur... ... Ornathine “piled up”Ornathine “piled up”

One Gene, One Enzyme One Gene, One Enzyme HypothesisHypothesis

-Beadle & Tatum

The media that The media that allowed growth, allowed growth, would show where the would show where the metabolic defect metabolic defect (mutation) occurred (mutation) occurred there was always a there was always a “pile up” of the “pile up” of the amino acid beforeamino acid before

One Gene, One Enzyme One Gene, One Enzyme HypothesisHypothesis

-Beadle & Tatum

If we inactivate one gene, that would code for an enzyme

to carry out X -> Y conversion, no product X or Y is produced. If product Y is needed to ultimately produce arginine, no growth will occur

One Gene, One Enzyme One Gene, One Enzyme HypothesisHypothesis

-Beadle & TatumThe supplement that The supplement that allowed growth, allowed growth, would show where would show where the metabolic the metabolic defect (mutation) defect (mutation) occurredoccurred

One Gene, One Enzyme One Gene, One Enzyme HypothesisHypothesis

-Beadle & Tatum

One Gene, One Enzyme One Gene, One Enzyme HypothesisHypothesis

-Beadle & Tatum

ex. this mutant grew (was able to complete the pathway) in the vial supplemented with Citrulline.

therefore, it must be defective in synthesizing Citrulline~ornithine piled up

One Gene, One Enzyme One Gene, One Enzyme HypothesisHypothesis

-Beadle & Tatum

each each genegene dictates dictates the production of the production of one one enzymeenzyme

each each mutantmutant lacks lacks the ability to the ability to produce an produce an enzymeenzyme

*Some proteins are not *Some proteins are not enzymes enzymes (ex. insulin)(ex. insulin)

*Some proteins are made of *Some proteins are made of more than one polypeptide more than one polypeptide chain chain (hemoglobin)(hemoglobin)

*Each chain specified by its *Each chain specified by its own geneown gene

One Gene, One One Gene, One PolypeptidePolypeptide HypothesisHypothesis -Beadle &

Tatum (revisited)

How are enzymes How are enzymes (proteins/polypep(proteins/polypep

tides) made?tides) made?

How do we How do we get from DNA get from DNA to protein?to protein?

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RNARNA is is the the bridge bridge between between DNA and DNA and ProteinProteinmRNAmRNA

tRNAtRNA

This is theThis is the basic basic

process:process:

TRANSCRIPTIONTRANSCRIPTION

TRANSLATIONTRANSLATION

No nucleus, No nucleus, protein synthesis protein synthesis occurs same time occurs same time as transcription.as transcription. Transcription occurs Transcription occurs

in in nucleusnucleus-> pre --> pre -mRNAmRNA

Translation occurs Translation occurs on on ribos.ribos.

DNA -->DNA -->RNA -->RNA -->

PROTEIN!PROTEIN!

U not TU not T

TripletsTriplets - - series of three series of three nucleotides- nucleotides- code for Amino code for Amino Acids Acids

((1961)1961) MarshallMarshall NirenbergNirenberg deciphered deciphered first first codoncodon..

((1961)1961) MarshallMarshall NirenbergNirenberg deciphered deciphered first first codoncodon..Won Nobel prize in

Physiology and Medicine 1968 for the

interpretation of the genetic code and its function in protein

synthesis.

1965 Dictionary of Amino Acids

1965 Dictionary of Amino Acids

Code Redundancy

•Third base in a codon shows "wobble”.

•First two bases are the most important in reading the code and giving the correct AA. The third base often doesn’t matter.