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Metabolism
The total reaction of the cell in which the enzymes
participate to exchange matter and energy between the
cell and its environment .
-In order to stay a life the cell should keep an energy
supply for the essential metabolic activities .There are
thousands of chemical reactions taking place with the
cell and out of the cell in order to perform certain
function .These reactions involved as exchange of the
matter and energy .This energy is either utilized or
evolved.
-These chemical reaction can involve:
Oxidation,Reduction,Hydroxylation,Carboxylation,
Condensation, all of them are catalyzed by enzymes
-So as a result of metabolism we have energy
production,e.g In oxidation of protein.
Function of Metabolism
1-Energy production, e.g The oxidation of protein, F.A,
Glucose, Acetyl-CO-A is formed, enter the pathways of
produce energy, but when energy production inhibited,
death occur.
2. Building units production, e,g. amino acid, F.A. &
simple they important for building new structure because
of the continuous breakdown of the body tissues which
must be replaced.
3.The synth. of protein: from the amino acids , lipids
from F.A., nuclic acid (N.A.) from purine, pyrmidine.
4. Special cellular function molecules, e.g. mitochondria,
in the cell membrane (phospho-lipids) are important in
the permeability of the cell membrane, polysaccharides
are import in the cell – cell recognition.
*sources of energy: the main source is the sun light
usually plants take the sun light with CO2 + H2O to
produce glucose.
- The metabolism can be classified into tow types:1. Catabolism.
2. Anabolism.
* Catabolism (catabolic metabolism):
Degradation or the breakdown of the large molecules
into simple ones.
- Catabolism has 3 stages:a- Conversion to building units.e.g.
Polysacch. --------- Hexoces (6C) or Pentose (5C)
Lipids
F.A. + glycerol
Protein
A.A.
b- The formation of acetyl-co-A:
The conversion of all these substances (hexoses,
pentoses, F.A., A.A.) into 2 carbon compound which is
Acetyl-CO-A which is common among all these
nutrients.
c. Oxidation of the Acetyl-CO-A into Co2 + H2O. the
energy is produced as (ATP) in krebs TcA cycle.
* These catabolic stages are all associated with the
liberation of energy.
The energy produced takes place in the catabolism.
*Anabolism: The process of biosynthesis &
collection of small molecule & synthesis of large ones
(condensation of small molecule). It is the reverse of
catabolism.
Ctab. Large
small
Anab. Small
large
a.a
protein
F.A. + glycerol
fats (Triglyceride)
* Anabolism is characterized by the use of the energy
produced by catabolism.
i.e, (ATP) is produced by catabolism & utilized by
anabolism.
* The two processes occur at the same time but in
different compartment – Anabo. in cytoplasm – catab. in
mitochondria.
e.g. F.A. oxidation in the mitochondria.
F.A. synthesis in the cytoplasm.
* Note: The same enzyme catalyzed the catabolism & the
anabolism.
e.g.
Glucose
E1
pyruvate
E2
lactic acid.
This process is called (glycolysis).
While
Lactic acid
E3
pyruvate
E4
glucose.
This process is called (glyconeogenesis).
e.g. glycogen
lactic acid need 12 enzymes.
Lactic
glycogen needs 9 enzymes.
* The catabolism & the anabolism can not catalyzed by
the same enzymes because:1. They occur at the same time.
2. One of them involves ATP production & the other
ATP utilization.
Catabolism involves energy production.
Anabolism involves energy reduction.
* Catabolism & anabolism could be represented as a tree
Polysacch.
Protein
Glucose
A.A.
Lipid
F.A.+ glycerol
Acetyl – CO – A
H2O
CO2
ATP
* The types of the energy which are involved in
metabolism:1. Potential energy: energy stored in the organ molecules
Sun light
Glucose, Lipid, proteins
CO2 + H2O + Energy.
[o]
2. Free energy: energy which can do work at a constant
temp. & pressure.
* In any living organism
- Isothermal: no heat is used for doing work.
- Use the chemical energy (energy stored in ATP
molecule).
* ATP is synthesized from the phosphorelation of ADP.
This occurs with the oxidation reactions:
ATP formation:ADP + Pi
ATP
- Enzyme reaction couples oxidation reactions.
* When the ATP is formed it will diffuse from the site of
production to the sites of utilization in the cell. ATP
energy is transferred to an acceptor molecule & used
when needed.
Electron transfer system:One of the systems (in respiratory chain) transferring the
energy from catabolic process to anabolic process &
usually Co-enzymes such as NADP is needed for this
processes.
NADP + H
NADPH
Energy is produced as a result of transfer of this
electrons at the presence of these enzyme.
Metabolic turnover:Continuous synth. & degradation of tissue or nutrients to
keep a constant conc. of the cell constituent.
In the cell there are different organelles & enzymes when
there is any process( metabolic process). There is a
utilization of material & breakdown of cells in contact
with the process. these damaged cells are replaced.e.g. in
any enzymatic reaction the enzymes are exhausted , this
exhaustion renders the enzyme inactive, so the body
needed new enzymes , as a result there is always
inactivation or activation of the enzymes. All the damage
cells will be replaced so that to keep same conc. of the
cell constitutes const.
*This turnover varies from one organ to another , e.g. in
the liver & intestine is more rapid than the other tissues,
because: many exogenous compound come to the liver or
intestine where it is detoxified [function of the liver the
detoxification of the exogenous toxic materials] so the
enzymes which are present in them are more active & are
damaged & replaced very rapidly, i.e. turnover
(metabolic turnover) is high which in less active tissues,
such as lipid the turnover is slow.
The Metabolism
This is done by:
1. Identification of chemical path way.
- Identification of each product
- Identification of each enzyme.
2. The regularity mechanism of the reaction rate to
specify which enzyme is a regulatory one.
 If the whole seq. Contain 10 enzymes, three
enzymes of them are regulatory, all are not affected
except the 3 enzymes.
 The 3 enzymes are regulatory when there is an
accumulation of the produced the rate of the
enzymes are reduced & the 3 enzymes rate increase.
In the diabetes mellitus (un controlled)
- The glucose pathway becomes the minor.
- The fat pathway becomes the major.
Fat produces more acetyl COA, this acetyl COA will be
in excess of kribs cycle capacity, some of them go to the
formation of keton bodies (acetone bodies).
* Normally these K.b. are not present or little.
- Amount of CO2 in glucose production will be less in
diabetic person.
Glucose
[O]
CO2
F.A oxidation
K.B.
(decrease)
(increase)
Accumulation
Certain type of a.a., tyrosine & phenyl alanin. Produce
keton bodies, so we call it (ketogenic a.a.)
Tyrosine & phenyl alanin produce
AC.AC (K.B)
Inhibitors:
It has been found when fluorocitrate is present. It will
inhibit citric acid cycle (C.A. oxidation)
Fluorocitrate
citric acid accumulation
Acetoacetate
Cellular regulation of the metabolic
pathway:
Rate of cellular
Catabolism (cata.)
cellular need
of energy (E)
 If cellular need of E , rate of cata.
 Changes every second (occurs instantly) also the
need of intermediates in the cell & the rate of
biosynth.
 When there is enough intermediate biosynth.
 When intermediates go short the rate & biosynth de
 There is balance between E need & the rate of cata.
Level of regulation:
1.Reactants & products:
enzyme kinetic activity depend on: - pH
- Substrate conc.
- Product conc.
- Co – enz.
* In living sys. usually PH & Co – enz. Constant.
2.Regulatory enzyme:
When accumulation of end product give signal to
enzyme to
(a feed back inhibition) or it could be
stimulated when there is excess metabolitic.
* So, inhibition by the end product or stimulation by
special metabolite.
3. Genetic control of enzyme synth:Concentrate of active from of enzyme balance between
synth. & degradation.
* Enzyme synth. Is controlled by genes in the DNA.
4. Hormonal control:
This is important in the high multicellular organism.
Insulin deficiency
a. failure of glucose transport
across the cell.
b. FA synth.
c.
KB ketone body synth.
* The rate of Rx. is change according to type of
hormone which is stimulated.
CHO Metabolism:
CHO is a type of compound contain C, H2, O2
 {H2 , O2} in the same ratio that as water could be
classified to:
 Simple sugars: glucose, fructose, galactose,
(( Monosacch. ))
ribose
 Disacch.:
Sucrose.
Glu. + Fru.
Lactose
Glu. + Gala.
Maltose
Glu. + Glu.
Formed from hydrolysis of starch
 Polysacch.: starch, cellulose, glycogen.
In dief. the most common one is starch, which comes
next glu, fru., gala.
** Lactose present in milk.
 Digestion:
Mouth
Starch
contain many glu.units
Salivary amylase
amylopectin + amylose
In starch:
One chain connected to the other by 6 glycoside linkage
* In the mouth starch is hydrolyzed by amylase enzyme
to amylose & amylopectin (( 1,6 linkage is broken )) this
hydrolysis taken place in mouth only.