Can you give me a good way to understand, explain and illustrate what
pH is and what it means, chemically speaking?  Where I'm headed with
this is to try to get a better understanding how and in what way pH is
significant to the biochemical functions of the body...

Hello jat-ga 

Thank you for your good question about pH. The dictionary definition
of pH will tell you that it is a measure of the concentration of
hydrogen ions in a solution. It's really how much or how little
hydrogen ions in a solution that determines where it lies on the pH
scale.  The more hydrogen ions the more acidic the solution is, the
less hydrogen ions the more alkali the solution.


The concise medical dictionary has this definition at
http://www.xrefer.com/entry.jsp?xrefid=128489&secid=.-

With a slightly more technical defintion from the The Macmillan
Encyclopedia 2001 at
http://www.xrefer.com/entry/512591 
Which talks a little more about the pH scale

But I guess what you're really asking is more about how hydrogen ions
floating around in the body and interacting in various biochemical
reactions actually does anything?

Think about hydrogen ions as being these charged up reactive
particles, sort of like reved up engines. In fact a hydrogen ion is
positively charged as it has lost it's only electron, so really it's
just a proton whizzing around, it desperately wants to get hooked up
with some electrons.

One really important place that hydrogen ions get 'used' or rather
'moved' is in the mitochondria (the little power house of the cell) In
this mitochondrian these hydrogen ions are pumped between two
membranes. This sets up a difference in concentration of hydrogen ions
(that pH scale) so one side of the membrane has lots of hydrogen ions
. The mitochondria can then let some hydrogens pass through special
proteins and in the process transfer all that hydrogen ion energy into
a useful energy molecule called ATP that can then go around the  cell
to do other useful things (like contract muscles).

This situation is very similar to a dam and hydroelectric station. As
the water from the dam rushes through the turbine it creates
electricity. In the mitochondria it is not a large volume of water but
rather a difference in hydrogen ion concentration. It's simialr to the
way a battery works also,one part of the battery has more electrons
than the other and they all want to rush and spread out but if you use
a wire you can control how they get through. Mitochondria are like a
battery in some way they have a positive and negative part to them.

You can see a picture of this at 
http://cellbio.utmb.edu/cellbio/mitochondria_1.htm

But they call it a "large electrochemical proton gradient" Which just
means a big difference in pH from one side to the other side.

So it's really important that the pH is correct in different parts so
of the body or cells sol they can function properly, especially the
mitochondria.

Should you have any further questions or if I can clarify anything
please don't hesistate to ask. I have a degree in biochemistry and
molecular biology and I'm happy to explain in more detail.


search strategy

google
pH explained
mitochondria hydrogen concentration

www.xrefer.com
pH

For nice images of the pH scale try
http://images.google.com/images?hl=en&lr=&ie=ISO-8859-1&q=pH+scale

---

Request for Answer Clarification by jat-ga on 26 Aug 2002 22:24 PDT

I suppose I should have been a bit more specific, but let me see if I
can phrase this a bit differently with respect to the "why" of it all:
 The blood pH is carefully regulated by the body to be close to 7.4
and the interstitial fluids usually are more alkaline in a healthy
body.  In the stomach, pH is obviously low, but it is rapidly changed
as food passes into the small intestine and a shot of bicarbonate is
delivered by the pancreas to effect a change in pH towards alkaline. 
Why is all of this necessary? and for what reason?  Hope this helps...

---

Clarification of Answer by rcd-ga on 27 Aug 2002 15:04 PDT

Hello jat,

Thank you for your clarification question. The most immediate answer
to the 'why of it all' is primarily related to the way all the enzymes
and proteins in the different parts of the body work.

The activity of enzymes in the body is very dependent on the pH
condition. In the stomach for example there are enzymes that only
operate at very low pH conditions. The physical structure of enzymes
relies on their surrounding solution to 'bend' into the right shape
for the enzyme to act properly.

In the blood for example there are enzymes, related more to the
ability to exchange CO2/O2 , CO2 has a tendency of increasing the pH
of blood and impairs the ability to take up oxygen into blood cells.

As mentioned previously though changing the pH in the blood will
change the way the other proteins and enzymes in the blood will be
shaped. Recall that hydrogen ions are charged and so tend to want to
attach to other things including parts of enzymes this ends up
physically changing their structure.

There is a great looking resource on enzymes at
http://users.rcn.com/jkimball.ma.ultranet/BiologyPages/E/Enzymes.html


The key issue on the above URL reference in regard to pH is...

"Changes in pH alter the state of ionization of charged amino acids
(e.g., Asp, Lys) that may play a crucial role in substrate binding
and/or the catalytic action itself. Without the unionized -COOH group
of Glu-35 and the ionized -COO- of Asp-52, the catalytic action of
lysozyme would cease. "

Which is technical way of saying " pH changes the shape of the enzyme"


A discussion on blood and haemoglobin function can be found at
http://www.biosci.uq.edu.au/GMC/haemoglob99.html

I hope this clarifys your question. 

kind regards

rcd-ga

Helpful.  I'm sure I'll be back for more...