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Metabolism_ The

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Metabolism: The COMBINATION of all
the chemical reactions        which occur in
an organism’s cells. Metabolic reactions can
be divided into two categories:
Anabolic        and catabolic reactions.
The metabolism of all organisms involves
both of these reactions.

Anabolic Reactions: sets of metabolic
reactions in which     enzymes        are
used to reorganize and combine
    simple      molecules into complex
molecules. Thus, anabolic reactions are net
energy consumers . Examples of
anabolic reactions include food (e.g.
glucose) producing reactions such as
photosynthesis found in autotrophic
organisms. All organisms use the anabolic
pathway called protein        synthesis to
produce proteins.
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Catabolic Reactions: sets of metabolic
reactions in which      complex molecules
(e.g. glucose) are broken down into simpler
molecules resulting in the release of ATP
(energy) . Thus, catabolic reactions are net
energy producers . All organisms use
catabolic reactions, including     cellular
    respiration.

Some Key Definitions
1. Substrate: the initial reactants in and
enzyme catalyzed reactions. When the
substrate binds to the enzyme’s active site,
the enzyme - substrate complex forms.

2. Product: The    substrate(s)     is/are
converted into the product (s) in a reaction.

3. Cofactor: Non- protein helpers which
assist the enzyme      in its catalytic
function. Some cofactors are inorganic
particles like metallic ions (eg. Calcium)
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4. Coenzymes: large organic cofactors.
They serve as carriers for chemical groups
or electrons        involved in the reaction.
Vitamins such as niacin           ,
    riboflavin     ¸ thiamine, make up a
large part of some coenzymes. Like all other
cofactors, coenzymes are not made of
protein .

Thyroxin and Metabolism
- thyroxin is a    hormone
Source gland for thyroxin: thyroid gland
    (found in front of the throat )

Function of Thyroxin:     increase
cellular   respiration
 = Increased energy (ATP) consumption
 = increased heart rate
 = increased synthesis of catabolic enzymes

** Thyroxin also seems to be involved in
regulating body
temperature     and in           reactions.
                 Metabolism                    4


( cold stress greatly   increases   thyroxin
production      .




Control of thyroxin:
Hypothalamus (in brain)
               Thyroid Relasing Hormone
or Thyroid release-inhibiting Hormone
                   
           Pituitary gland (anterior)

        TSH (Thyroid stimulating hormone
          

Thyroid gland

            thyroxin

***** Thyroxin needs     iodine !!
No iodine = increase in thyroid cells
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= GOITER

				
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