one gene - one polypeptide

[whatbetch]

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I still don't understand why 'one gene - one protein' was changed to 'one gene - one polypeptide'... i know it has something to do with proteins containing more than one polypeptide chain, cause that's what i've read in textbooks... but it still doesn't make sense to me so could someone please explain it to me?! Thanks.

[sam5]

Originally Posted by whatbetch

I still don't understand why 'one gene - one protein' was changed to 'one gene - one polypeptide'... i know it has something to do with proteins containing more than one polypeptide chain, cause that's what i've read in textbooks... but it still doesn't make sense to me so could someone please explain it to me?! Thanks.

Alright. Heres a thing u should remember. Atoms form amino acids. Amino acids form polypeptides. Polypeptides form Proteins. Basically, Beadle and Tatum thought that every gene (thus, one gene) lead directly to the formation of one protein (thus, one protein). However, (as u learned from protein synthesis processes) you would know that genes lead to the direct formaiton of polypeptides, not proteins. Proteins are indirectly formed, but this is a step later, when polypeptides themselves (produced from genes) are binded together to form protenis. So basically, Beadle and Tatum thought that every gene made one protein, but it was actually found that every gene made one polypeptide instead. Beadle and Tatum wernt completely incorrect, cos these polypeptides (produced from the genes) do eventually form proteins, but they were one step ahead of themselves.

[clarebear14]

Originally Posted by sam5

alright. Heres a thing u should remember. Atoms form amino acids. Amino acids form polypeptides. Polypeptides form proteins. Basically, beadle and tatum thought that every gene (thus, one gene) lead directly to the formation of one protein (thus, one protein). However, (as u learned from protein synthesis processes) you would know that genes lead to the direct formaiton of polypeptides, not proteins. Proteins are indirectly formed, but this is a step later, when polypeptides themselves (produced from genes) are binded together to form protenis. So basically, beadle and tatum thought that every gene made one protein, but it was actually found that every gene made one polypeptide instead. Beadle and tatum wernt completely incorrect, cos these polypeptides (produced from the genes) do eventually form proteins, but they were one step ahead of themselves.

i needed help with this crappy thing aswell and it finally makes sence.. Thank you

[whatbetch]

okay thanks.. so does the hypothesis relate to the process of protein synthesis and in a way what happens if one step is mutated along the way?
i think i get it a bit better now thank you!

[sam5]

Originally Posted by whatbetch

okay thanks.. so does the hypothesis relate to the process of protein synthesis and in a way what happens if one step is mutated along the way?
i think i get it a bit better now thank you!

pardon? What r u tryin to say? :-|

[sam5]

ahh hang on i get ya now. Yeah its sayin that if there if a mutation, it will affect what type of polypeptide is produced. This will in turn affect what types of proteins are made. Proteins are essential, and include standard proteins, homones and enzymes. Other self made biomolecules also fall under the bracket of proteins. In the beadle and tatum experiments, they exposed some bread mould to x rays. This caused them to have mutations, and these mutant mould would die unless they were given a nutrient solution by the scientists. This nutrient solution kept them alive, because this replenished them with the proteins that they needed to live. They normal mould not exposed to the x rays didnt need the solution, because they had normal genes, and thus could make their own correct polypeptides (and thus proteins) to keep them alive. The mutants could not live without the solution, because their genes were altered, and therefore the proteins they were making from polypeptide synthesis were altered. Because they were altered, they didnt work properly. Plus, the production of this new (bogus) protein was a replacement for a protein needed for life. Without this protein, they would die (but the didnt die cos of the nutrient solution given to them). I know thats a whole heep of info, but i hope it makes sense. :-)

[annikab]

Beadle and Tatum were not wrong in their hypothesis or experiment. They were just essentially lucky that the production of arginine (a nutrient needed for growth) in bread mould is only controlled by one polypeptide, which is in turn controlled by one gene.

Their theory had to be changed however, as this is not applicable to all living organisms. In fact, many genes control the production of one protein (= many polypeptide chains bound together).

[christoffpow]

Originally Posted by whatbetch

I still don't understand why 'one gene - one protein' was changed to 'one gene - one polypeptide'... i know it has something to do with proteins containing more than one polypeptide chain, cause that's what i've read in textbooks... but it still doesn't make sense to me so could someone please explain it to me?! Thanks.

'Neospora Crassa' was the bread mould they experimented with. Basically they exposed the bread to x-rays to induce mutations in the particular gene sequences, that were required to produce the polypeptide controlling the growth of the mould. Hence, these mutations led to the production of disfunctional polypeptides (enzymes), which led to the inhibitation of bread mould (mould would not grow). Beadle and Tatum discovered the mould would grow, however, when a specific amino acid was added to the bread. This led them to discover the one gene one enzyme theory... that for every enzyme there lies a particular gene sequence. this was later changed to one gene one polypeptide because not all genes code for enzymes, and that genes are not the only form of proteins. Genes also code for structural proteins (the shape of your nose), and hence the theory was later refined to 'one gene-one polypeptide' = structural proteins and enzymes are both polypeptides.

[christoffpow]

Originally Posted by annikab

Beadle and Tatum were not wrong in their hypothesis or experiment. They were just essentially lucky that the production of arginine (a nutrient needed for growth) in bread mould is only controlled by one polypeptide, which is in turn controlled by one gene.

Their theory had to be changed however, as this is not applicable to all living organisms. In fact, many genes control the production of one protein (= many polypeptide chains bound together).

Yep. they were really lucky with their choice of experiment.