HELP! WITH BIOCHEM QUESTION

Ben Levin benjinsl at astro.ocis.temple.edu
Sun Jun 11 15:13:48 EST 1995


Gideon,

Being a biochem major,  I actually apologize for not having answered 
you're previous queries on this group.  Anyway,  now I'll try to make up 
for it.

I.  I'll answer your last question first,  merely because it's a hell of 
a lot easier than the first.
 Enzymes react with a whole slue of materials.  _Proteases_ react with 
other proteins by hydrolyzing them,  meaning they "add" water (hydro) to 
the bonds between the Carbon-Nitrogen bond in the backbone of the 
protein,  while breaking this bond apart,  thus shortening or breaking 
apart the protein being hydrolyzed.  _Kinases_ add an inorganic phosphate 
molecule (Pi) onto a variety of other molecules.  Some kinases add Pi 
onto other enzymes,  some add it onto sugar molecules.  _Phosphatases_,  on 
the other hand,  remove Pi from molecules.  One enzyme, RUBISCO 
(ribulose-1,5-bisphosphate carboxylase/oxygenase) is the most abundant 
one on the planet (an estimated 10 kilo.'s per person on the earth) as 
well as the key enzyme in photosynthesis.  It catalyzes the addition of 
carbon dioxide to the sugar phosphate (a sugar molecule with phosphate 
groups bonded to it) ribulose-1,5-bisphosphate (as the name implies).
 In general there are 6 enzyme types as classified by reaction type.
	1.  Hydrolases-hydrolysis reaction (protease)
	2.  Transferases-transfer of functional groups
	3.  Oxidoreductases-oxidation-reduction reactions
	4.  Lyases-group elimination to form double bond
	5.  Isomerases-isomerization
	6.  Ligases-bond formation coupled with ATP hydrolysis
II. " and would like to know how enzymes dont need activation energy to 
cause a rection with a substrate."
 For all reactions, regardless of whether or not there is an enzyme 
present or not,  there is an activation energy.  The activation energy is 
the energy needed to overcome the energetic barrier from reactants to 
products.  Thus,  all reactions have an activation energy assacioated 
with them.  [The reason that some reactions happen spontaneously and 
seem to have no trouble happening,  such as the evolution of carbon 
dioxide bubbles caused by adding vinegar to baking soda,  is that the 
products are much more stable].  What enzymes,  and all catalysts,  which is 
what an enzyme is, do is to lower the activation energy.  This happens 
with enzymes by the enzyme "holding" the substrate in such a way as to 
cause the reaction,  thus leading to products,  to be much more favorable 
compared to the reaction taking place without an enzyme.
 This is a very crude explanation,  so I won't be surprised if you have 
any questions which I will be delighted to attempt to answer.

Ben
benjinsl at astro.ocis.temple.edu



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