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Dr. R. A. Savidge savidge at unb.ca
Tue May 2 07:20:32 EST 1995

In message 2 May 1995 10:31:55 GMT,
  gideon at iaccess.com.au (GIDEON BAKER)  writes:

> In article <3o51f4$2l6 at sleipnir.iaccess.com.au>, gideon at iaccess.com.au
> (GIDEON BAKER) says:
>>   I am new to botany  and would appreciate if somebody could explain the
>> following:
>>   I understand that plants make agreat variety of compounds from  raw
>> materials.  Most of biological compounds fall into just four caterories:
>> carbohydrates
>>  lipids,proteins and nucleic acids.
>>   Given that this is correct, does this mean that all these comounds
>> essentially consist of the same elements and are just ISOMERS ?
>>  Please could somebody explain this.

Dear Gideon,
The elements in carbohydrates are carbon (C), hydrogen (H) and oxygen (O).
Lipids also contain C, H and O, but they contain less O.  Proteins  and
nucleic acids also contain CHO, but in addition all proteins have nitrogen
(N) and sulfur (S).  All nucleic acids (DNA and RNA) have N
and phosphorus (P) as well as C, H and O.  Carbon dioxide (CO2) is the main
source of C and also a source of O; water (H2O) is the main source of H
and O; soil is the primary source of N, P and S.  Metabolism in the plant
converts these simple molecules into more complex ones, rather like a
builder utilizing different materials to build a house.

The word `isomer' means that there are two or more substances composed
of molecules having exactly the number of each kind of atom (another
word for element), but each isomer has the atoms in a unique arrangement.
Consequently, each molecule within an isomeric group has chemical
properties different from the other isomers.

Carbohydrates are a class of molecules many of which are isomers.  Lipids
are another class of molecules, also containing many isomers.  In general,
a carbohydrate molecule is not an isomer of a lipid molecule because they
do not have exactly the same number of each kind of atom (the C:H:O
proportions are different).  A protein molecule cannot be an isomer of
either carbohydrate or lipid molecules because proteins have N and S.  The
same reasoning applies to nucleic acids.

I hope this helps!
   Rod Savidge, PhD                 |         E-mail: savidge at unb.ca
   Faculty of Forestry and         \|/
      Environmental Management  \   |   /     Phone:  (506) 453-4919
   University of New Brunswick  _\/ | \/_
   Fredericton, NB CANADA          \|/        Fax:    (506) 453-3538
   E3B 6C2                          |

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