Wikipedia:Reference desk/Archives/Science/2012 November 5

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November 5

Impulse (physics)

In this article, it states there are 2 different units. I don't understand how those 2 different units can end up expressing the same thing in the end?174.20.101.190 (talk) 01:21, 5 November 2012 (UTC)

They are equivalent: ${\rm {N\cdot s=kg~{\frac {m}{s^{2}}}\cdot s=kg~{\frac {m}{s}}}}$A8875 (talk) 01:50, 5 November 2012 (UTC)

And, they help remind physicists about the two commonplace ways we calculate impulse: the impulse of an event is often computed by multiplying the net force by the duration of the event; or, the impulse of an event is calculated by multiplying a mass by its total change in velocity. Nimur (talk) 03:07, 5 November 2012 (UTC)

Mechanism from DNA to proteins etc?

Is the mechanism between DNA and actual proteins etc that are created mapped out?, such that one can use the DNA to calculate (dry run a cell) how the produced protein etc looks like? Electron9 (talk) 03:58, 5 November 2012 (UTC)

See Transcription (genetics), Translation (genetics), Genetic code, Protein structure prediction. It's probably best for you to make a quick first pass through these articles and say what parts of the topic still confuse you after that. Wnt (talk) 04:16, 5 November 2012 (UTC)

Yes, specifically genetic code. The genetic code is the recipe for translating from sequences of DNA bases to the sequences of amino acids that make up proteins. It is astonishingly simple. If you know the code, you don't have to know anything about the mechanism that implements it in order to predict the result. (Well, there are a few complications, but they can be ignored on a first pass.) Looie496 (talk) 05:12, 5 November 2012 (UTC)

Yes, the genetic code is astonishingly simple. But you also have to take into account post-transcriptional modifications and posttranslational modifications. And when you have done that, you only have a protein's amino acid sequence. Inferring a protein's structure and function from its sequence is very difficult. Then you need to work out how it interacts with other proteins and chemicals in metabolic pathways. Then there are the complications of gene regulation. Taking all that into account, being able to "dry run a cell" (however we interpret that) is going to be a massively complex undertaking. The genetic code is just a snowflake on the tip of the iceberg here. Gandalf61 (talk) 12:17, 5 November 2012 (UTC)

The idea (dry run) is to make a computer simulation that is feed with the DNA code. Once the proteins etc has left the cell other software can simulate the chemical reactions. As for fenotypic gene enable/disable I guess those are in turn controlled by other genes and their resulting structures interacting with environmental chemistry as a feed back loop. Is that mechanism fully understood? Electron9 (talk) 16:12, 5 November 2012 (UTC)

No I don't suppose it is "fully understood", or even close to that, except in very limited cases. The cellular model article makes interesting reading. It says "The complex network of biochemical reaction/transport processes and their spatial organization make the development of a predictive model of a living cell a grand challenge for the 21st century.". According to this report, the best we can do so far is to build a computer model of mycoplasma genitalium, a bacterium with just 525 genes. Gandalf61 (talk) 17:11, 5 November 2012 (UTC)

(e/c) The DNA will tell you the order of amino acids, but knowing the order of the amino acids tells you very little about the functionality, which is often determined by the shape of the resulting protein. There's some active research on exactly how that folding works and how those shapes are determined, including a distributed computing project for the "heavy lifting" of just crunching how all of those pieces fit together. In all likelihood there are important mechanisms we aren't even aware of. 150.148.0.65 (talk) 17:34, 5 November 2012 (UTC)

Hot off the presses: [1] Wnt (talk) 23:17, 7 November 2012 (UTC)

Maybe not a science question?

Clinical laboratory science, and maybe more of a legal question than anything else, but every set of clinical laboratory results I've ever seen has a statement that says that partial reproduction of the test report is not permitted. Is this just a "don't interpret single test results without seeing context" warning? 150.148.0.65 (talk) 17:34, 5 November 2012 (UTC)

Is a full reproduction allowed, and a partial not? Otherwise, if neither a full nor a partial reproduction is allowed without consent, that would be a common copyright notice. OsmanRF34 (talk) 18:02, 5 November 2012 (UTC)

To quote some sample text "Partial reproduction of this Test Report is not permitted" (at top of each page of a set of test results). The sample is from a Indian reference laboratory, but I've seen a lot of the same in American test results. It says nothing about prohibition of full reproduction. Looking at a couple of other things I have lying around it isn't 100%, one of the ones I found (American) just explicitly labels full and partial reports. 150.148.0.65 (talk) 18:29, 5 November 2012 (UTC)

I think any claim that partial reproduction is forbidden may be void due the "Quotation#Copyright law". In addition foreign law isn't likely enforceable in another country. Electron9 (talk) 18:59, 6 November 2012 (UTC)