Monday, November 29, 2010
Last PyMOL assignment: G-proteins (the only PyMOL exercise for the final exam)
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synthesis of fat and phospholipid
cholesterol synthesis and transport
The atherosclerotic "plaque" is actually an inflammatory state, a growth of cells caused by the
body’s system for responding to inflammation.
Medical doctors refer to it as a “lesion”.
It is a
misconception that cholesterol just builds up in a heap on the arterial wall, like deposits inside a
Instead, the arterial “lesion” is a kind of inflammation: white blood cells migrate to
the site in the artery where LDL have been taken up.
The white blood cells engulf the LDL,
becoming so-called "foam cells" when they have taken in a lot of LDL.
The foam cells send out
signals to other cells in the immediate vicinity, such as muscle cells, to grow, to divide, and to
migrate to this area.
The result is a growing mass in the artery.
It is a benign, and cannot
However, the most deadly aspect is that the surface can "crack" or otherwise
become damaged, then a blood clot will form at that spot.
Pieces of the clot can break off and
travel in the blood until they lodge in a smaller artery, cutting off further blood flow.
actually the most deadly aspect of atherosclerosis.
We will talk about synthesis of nitrogen-containing molecules when we return from the break.
Next we consider how living systems can "fix" N
gas into ammonium ions, then into N-
containing compounds, LG page 272:
Only a few prokaryotes (termed
) can take atmospheric N
(gas) and reduce it ("fix" it) to NH
Although few, these few species are abundant:
In the soil:
Azotobacter, Klebsiella, Clostridium
In fresh and salt water:
Symbiotic with legumes:
The overall reaction that occurs is the following:
This reaction can be displayed on a free energy diagram, with the reactants at a higher free
energy than the products.
The negative value of
' tells us that the reaction is favorable,
under standard conditions.
But the transition state between the reactants and the product is
This is because the bond between the two nitrogen atoms is a strong, triple
To break this takes a