This document provides an overview of iron metabolism and metabolic pathways. It defines metabolism as the process by which living organisms acquire and use free energy. Metabolic pathways involve consecutive enzyme reactions that produce specific products. Pathways are divided into catabolism, which breaks down nutrients, and anabolism, which synthesizes biomolecules. Key characteristics of pathways include irreversibility, different pathways for interconversion, committed first steps, and regulation. Pathways occur in cellular locations, and compartmentation allows specialized functions. The document discusses iron metabolism and homeostasis before introducing homework on these topics.

1. Biochemistry;SPB 213
•Porphyrines;
biosynthesis,
catabolisme de l’heme

2. Refferences
• Sophie Waldvogel,-Abramowski, Gérard
Waeber, Christoph Gassner, Andreas Buser,
Beat M. Frey,, Bernard Favrat,and Jean-Daniel
Tissot (2014) Physiology of Iron Metabolism
Transfus Med Hemother. 41(3): 213–221.
• Harpers illustrated biochemistry by Robert K.
Nurray, Daryl K. Granner and Victor W. Rodwell.
27th Edition page 495 to 585
• Textbook of Biochemistry with clinical
correlations by Thomas M. Devlin sixth edition
pages 546 -555,824-830, 1110 and 1113-1114,

3. Objectives
• Concept of metabolism
• Metabolic pathways
• metabolism of iron
• Home work

4. introduction
•
• Living organisms are not at equilibrium.
they require a continuous influx of free
energy to maintain order in a universe
• . Metabolism is the overall process through
which living systems acquire and utilize the
free energy they need to carry out their
various functions.
• coupling the exergonic reactions of nutrient
to oxidation to the endergonic processes
required to maintain the living state
• performance of mechanical work, the
active transport of molecules against
concentration gradients, and the
biosynthesis of complex molecules.

5. • despite complexity of their internal
processes, they maintain a
steady state.
This is strikingly demonstrated by the
observation
• that, over a 40-year time span, a normal
human adult
consumes literally tons of nutrients and
imbibes over 20,000 L
of water, but does so without significant
weight change.
• steady state is maintained by a sophisticated
set of metabolic regulatory systems.

7. Iron metabolism:
7

9. Metabolism
• series of consecutive enzymatic reactions
that produce specific products
Reactants, intermediates and products are referred to as
metabolites
• an organism utilizes many metabolites, it has many
metabolic
Pathways
Metabolism has been traditionally (although not
necessarily
logically) divided into two major categories:
•

10. 1. Catabolism or degradation
 nutrients and cell constituents are broken
down
 so as to salvage their components and/or to
generate energy
degradative metabolism ie converts large
numbers of diverse substances
(carbohydrates, lipids and proteins) to
common intermediates

11. 2. Anabolism or biosynthesis,
• biomolecules are synthesized from
simpler components
• intermediates are then further
metabolized in a central oxidative
pathway that terminates in a few end
products.

12. characteristics of metabolic pathways
1. Metabolic pathways are irreversible
• A highly exergonic reaction (having a large
negative free energy change)is irreversible
• it goes to completion
• it confers directionality on the pathway
• it makes the entire pathway irreversible

13. 2. Catabolic and anabolic pathways
must differ
• . If two metabolites are metabolically interconvertible
• the pathway from the first to the second must differ
from the pathway from the second back to the first
• because if metabolite 1 is converted to metabolite 2
by an exergonic process
• the conversion of metabolite 2 tometabolite 1
requires that free energy be supplied
• in orderto bring this otherwise endergonic process
“back up the
hill.”
. Consequently, the two pathways must differ

14. • The existence of independent
interconversion routes, is an important
property
because it allows independent control of
the two processes
.Eg. If metabolite 2 is required by the cell,
it
is necessary to “turn off” the pathway
from 2 to 1 while
“turning on” the pathway from 1 to 2.
. Such independent control would be
impossible without different pathways.

15. 3. Every metabolic pathway has a first
committed step.
• Although metabolic pathways are
irreversible,
• most of their component reactions function
close to equilibrium.
 Early in each pathway, however, there is an
irreversible
(exergonic) reaction that “commits” the
intermediate it produces to continue down
the pathway.

16. 4. All metabolic pathways are
regulated
• regulated by laws of supply and demand in
order to exert control on the flux of
metabolites
• The first committed step, being irreversible,
functions
too slowly to permit its substrates and products
to equilibrate
(if the reaction were at equilibrium, it would
not be
irreversible).

17. • Most metabolic pathways are therefore
controlled by regulating the enzymes that
catalyze their first committed step(s).
• This is an efficient way to exert control
because it prevents the unnecessary
synthesis of metabolites further along the
pathway
when they are not required.

18. 5. Metabolic pathways occur in
specific cellular locations.
• The compartmentation of the eukaryotic cell allows different
metabolic pathways to operate in different locations
• For example,ATP is mainly generated in the mitochondrion but
much of it is utilized in the cytoplasm.
• The synthesis of metabolites in specific membrane-bounded
subcellular compartments makes their transport between these
compartments a vital and biological membranes selectively
permeable
• In multicellular organisms, compartmentation is carried a step
further to the level of tissues and organs.
• The mammalian liver, for example, is largely responsiblefor the
synthesis of glucose from noncarbohydrate precursors
(gluconeogenesis