🚀 go-pugleaf

In article <726020993snz@lrts1.demon.co.uk>, grmd@lrts1.demon.co.uk ("Gareth R. M. Davies") writes:
|> Please can somebody give me an explanation of the Krebs (TCA)
|> cycle, and where it occurs.  I understand it occurs in the
|> mitochondria and may be connected with aerobic respiration in
|> cells.  Any easily readable references would also be helpful.
|> If you prefer to send to me directly, my email address is
|>     grmd@lrts1.demon.co.uk
|> -- 
|> Gareth R. M. Davies                    Work tel. +44 753 696777 x2613
|> Home tel. +44 344 21729                Work fax. +44 753 696254
|> 
|> 

The Krebs or TCA cycle is a series of enzymatic reactions found in nearly all
organisms ranging from bacteria to plants to animals. It has two main roles.
One is to oxidize a two carbon compound carried by a cofactor (acetyl-CoA)
derived from sugars, amino acids, and fatty acids (FOOD!), thus liberating a
source of high energy electrons which can be used to drive oxidative
phosphorylation, a means of generating energy for the cell. In aerobic
organisms, oxidative phosphorylation typically requires oxygen as a terminal
electron acceptor. A second role of the TCA cycle is to generate, again from
acetyl-CoA, four carbon building blocks for the synthesis of amino acids and
glucose. In eukaryotic organisms (plants, animals, and other non-bacteria),
the location of the enzymes of the TCA cycle is the matrix of the
mitochondria.  In bacteria, these enzymes presumably reside in the cytosol.

Any biochemistry text will have gobs of detail on the TCA cycle. I like
Stryer's "Biochemistry", especially his chapter on the integration of
metabolism.

Why are you wondering about the Krebs cycle?

In article <1993Jan8.174736.11471@leland.Stanford.EDU>,
kksng@leland.Stanford.EDU (Kenneth Kai-Sing Ng) writes:
|>
|>A second role of the TCA cycle is to generate, again from
|>acetyl-CoA, four carbon building blocks for the synthesis of amino acids and
|>glucose.

Some microorganisms (particularly the cyanobacteria) are capable of running
the TCA cycle backwards to generate pyruvate (and hence eventually glucose)
from acetyl-CoA.  This doesn't happen in most organisms, though.  Man and I
think all other mammals are incapable of net new glucose formation from
acetyl-CoA.  The seeds of plants, which are very active in such synthesis,
don't do so using the TCA cycle.  They use a shunt called the glyoxylate
cycle.  Most organisms lack two key enzymes necessary to run the glyoxylate
pathway and thus generate new glucose from acetate.

--PSW