Metabolism
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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Metabolism
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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Metabolism
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.
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Metabolism
( cold stress greatly
production
.
increases
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thyroxin
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
Metabolism
= GOITER
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