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Cells, Microbes & Viruses / How are genes turned on and off?

« on: 30/11/2009 14:00:29 »

Gene expression is controlled by regulatory factors. For example, to turn on Ras gene, it requires GTPase, meaning that GDP is phosphorylated to GTP, thus activating Ras pathway. It can be turned off by sensor molecules and other regulator factors.

This is not right.  The Ras protein is activated/deactivated by exchange factors GAP and GEF.  However, the Ras gene itself is not directly turned on or off.  One should make a distinction between the _gene_ and the _gene product_ (or protein), as it pertains to the question of OP.

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Physics, Astronomy & Cosmology / I have noticed that in space something always seems to revolve around something?

« on: 30/11/2009 05:59:20 »

When scientists give answers like this, they are not talking about shape in the normal way. What they are talking about is the overall geometry of space. In a spherical geometry, the angles of a very large triangle sum to less than 180 degrees. In a saddle geometry, the angles of a very large triangle sum to more than 180 degrees. In a flat shape, the angles sum to 180 degrees.

Yes, the 'shapes' that are given, such as "saddle" or "sphere" are in analogy with our intuition of 3D geometry.  In the analogy, the space under consideration is 2D but "embedded" in 3D.  For our 3D world, we might imagine that it's embedded in 4D (as Einstein did when he started GR, but discarded it later when he realized the embedding is not necessary mathematically).  The "shape" of the 3-space in the 4-space is what scientists mean by the shape.

PhysBang's reference to the angles of the triangle are one means by which we can measure this curvature of space.  We may set up a triangle by means of three lasers, as lasers travel in "straight lines" (or "geodesics" in the language of general relativity), and then proceeding to measure the angles subtended by each joining pair of lasers.  The sum of the angles indicates the curvature. 

You can analogize by thinking of what it would be like for 2D creatures living on a sphere to shine a beam of light.  The light ray would be forced to travel in the 2D space, tracing out a "straight line" in 2-space but in reality curving in the embedding 3-space.  In this case, a straight line is simply one which minimizes length.  A triangle drawn with light rays on a sphere this way would not have angles that add up to 180.

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Physiology & Medicine / Different fungus without any reason?

« on: 30/11/2009 05:47:46 »

May I suggest a series of control experiments where you put the same salt+sugar on two pieces of bread, or beta-gal on both, etc, and see if you do indeed get the same colonies now.  Your initial hypothesis (I'm just guessing here) is that the different sugars may be contributing to different kinds of growth, but there is a competing null hypothesis which says that it doesn't matter, you'll just get lots of different kinds of fungal growth no matter what kind of sugars there are because there are so many kinds of fungal spores floating around.  For example, this experiment showed different fungus (as indicated by coloration) growing on a single piece of bread: mold-garden (scroll down for the mold garden on the bread)

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Chemistry / Enquiry about oxygen reactive methylene blue ink

« on: 30/11/2009 05:39:52 »

the methylene dye and titanium nanoparticle mix seems to detect only presence of oxygen.  how would you harness it to detect deterioration of a pharmaceutical? each pharmaceutical decays with its own particular pattern of byproducts.  perhaps if the pharmaceutical produces oxygen in its deterioration?  the answer seems heavily chemical-dependent whether or not this is a good chemical sensor of deterioration.

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General Science / What is the result of 2/0?

« on: 24/11/2009 05:21:21 »

i agree with the above posters that it is a limiting process.

one question from me now, hopefully it doesn't derail this thread, but how did RD and lightarrow produce the infinity symbol in the post?