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METABOLISM-Introduction-
Serkan SAYINER, DVM PhD. Assist. Prof.Near East University, Faculty of Veterinary Medicine, Department of Biochemistry
Overview
Living organisms need the chemicals to renew themselves and to develop and reproduce. This is because, all organisms are formed from the chemical substances.
These chemical substances can be organic such as carbohydrates, lipids protein, or can be water and inorganic elements such as Ca,P, Fe, S. For example, skin is formed from water, proteins, lipids and inorganic materials, beside this cell membranes are formed from lipids and proteins.
The molecules that make up the organism either participate in the structure of the organism or participate in the functions that provide the formation and continuity of the structure.
Once ingested and absorbed molecules enter the cell, they participate in various biochemical reactions.
METABOLISM: It is the chemical reactions that occur within the
tissues and cells of a living organism and enables the production and
continuity of living matter.
ANABOLISM: To synthesize the compounds of structural or functional
molecules from matters taken from food or inside the organism. It is
also called the orientation of the constructions of metabolic
reactions.
CATABOLISM: Fragmentation of molecules synthesized by the
organism or cells imported into the cell, therefore the it can also
called degradation of the metabolic processess.
Anabolism + Catabolism = METABOLISM
Definitions
Exergonic Reactions: Some of the reactions occurring in the
body are energizing. This reactions are called exergonic
reactions.
Endergonic Reactions: Some of the reactions occurring in
the body are energy receiving. This reactions are called
endorgonic reactions.
Intermediate metabolism: The metabolic processes within
cells and tissues in the organism referred to by the term
intermediary metabolism. In other words, the set of reactions
within the cells is called intermediate metabolism.
Definitions
Foodstuffs entering the body express changes only after
they are absorbed in the digestive tract.
The anabolic and catabolic reactions in the intermediate
metabolism develop in steps, that is, the formation of a
number of intermediates.
In other words, the reaction takes place in the form of the
initial substance reaching the final product through
intermediates. Intermediate metabolic substances in this
type of reactions are called metabolites.
Definitions
Precursor
Intermediate
MetaboliteIntermediate
Metabolite
Intermediate
Metabolite
End-
Product
Metabolites
(Intermediate metabolik substances)
There is a wide variety of metabolic reactions in the
organism that occurs. It is possible to collect them
under 3 groups.
• Hydrolysis and Condensation
• Phosphate transport
• Biological oxidations
Reactions of Metabolism
CONDENSATION• A reaction in which two or more
molecules combine to form a larger
molecule, with the simultaneous loss of a
small molecule such as water
• Glycoside bond (between two
monosaccharide molecules in
combination with an ether linkage),
Peptide bond (between two amino
acids), ester bond (between glycerol and
fatty acids) are some examples.
• Condensation is an endergonic reaction
that energy is used.
Reactions of Metabolism
HYDROLYSIS• It is a reaction involving the breaking of a bond in a molecule using
water. The reaction mainly occurs between an ion and water molecules and often changes the pH of a solution.
• Polysaccharides with amylase, degradation of proteins with pepsin in the gastrointestinal tract, the cleavage of triglycerides to glycerol and fatty acids by lipase are some examples of hydrolysis events occurring in the body.
• They are exergonic reactions that release energy. 1-4 kcal of energy per molecule released.
• Hydrolysis events that take place under digestive enzymes in the organism and the body's temperature, can be formed by boiling with concentrated acid and alkaline in vitro.
Reactions of Metabolism
Sucrase
PHOSPHATE TRANSPORT• In organism, many molecules, especially carbohydrates, need
to be phosphorylated, i.e. phosphate esters, to be able to
enter into the reactions.
• In this task, phosphate carriers are loaded and phosphate
residues are given to the required molecules.
• Phosphate carriers are classified in 2 groups according to the
number of phosphate residues they contain.
1. One phosphate residue carriers
2. Multiple phosphate residues carriers
Reactions of Metabolism
1. One phosphate residue carriers• Molecules that carry enol, carboxyl, hydroxyl or an amino group
change its H atom with a phosphate residue (H2PO3-).
2. Multiple phosphate residues carriers• Examples of this group may be adenosine diphosphate (ADP)
and adenosine triphosphate (ATP). These materials can be
formed by replacing 1 hydrogen from an alcohol group of a
pentose nucleotide and receiving 2 or 3 phosphate residue.
Reactions of Metabolism
PHOSPHATE BONDS AND ENERGY
• Some molecules carrying a phosphate residue have weak
phosphate bonds and some have resistant bonds.
• Resistant phosphate bonds have weaker energy.
• Most of them are phosphate esters and it is possible to break
down with phosphatase enzymes in the organism and with
aqueous acids and alkalis in vitro.
• Degradation of Glucose-6-phosphate (G-6-P) to phosphate and
glucose releases low energy (3.3 kcal.
Reactions of Metabolism
• Weak phosphate bonds are bonds that break down and give
high energy.
• Acyl sulfates, enol phosphates, adenosine triphosphate
molecule are carrying this kind of phosphate bonds.
• They are destroyed with special phosphatase enzymes in
biological reactions, 7-13 kcal of energy is released. Thats
why these phosphate compounds are also called high-energy
phosphate compounds.
• For example, a phosphate and the ADP revealed with the
degradation of the ATP and the 7 kcal energy occurs.
Reactions of Metabolism
Phosphate inculing
moleculesBond type Reaction Kcal
Glucose-6-phosphate Ester G-6-P Gli + P - 3,3
ATP Phosphoanhydride ATP ADP + P - 7,0
ATP Phosphoanhydride ATP AMP + P + P - 8,6
Phosphoenolpyruvate Enolphosphate PEP Pyruvate + P - 13,0
Creatin phospahte Phosphamide Creatin-P Creatin +P - 10,2
Phosphate Bonds And Energy
All high-energy phosphate compounds serve as the phosphate
donor.
The hydrolysis of such phosphate compounds leads to energy
output. Among these, however, ATP, in particular, provides both
the necessary phosphate and energy for the destruction of
another molecule.
Phosphate and energy transport in the organism is under the
control of phosphokinase enzymes.
Reactions of Metabolism
BIOLOGICAL OXIDATIONS (Oxidation and reduction events)
• Transition of electrons from one atom or molecule to another
referred to as redox reaction (Redox: e- transfer).
• OXIDATION: It is the loss of electrons or an increase in
oxidation state by a molecule, atom, or ion.
• REDUCTION: It is the gain of electrons or a decrease in oxidation
state by a molecule, atom, or ion.
• Hydrogen ions are also seperated from the organic molecule with
the electrons. Thats why the simplest type of an oxidation is called
dehydrogenation.
• In organism, enzymes are also oxidized or reduced.
Reactions of Metabolism
Reactions of Metabolism
A
(reducing)
B
(oxidizing)
B
(Reduced)
A
(oxidized)
e-
e-
e-
e-
The most important electron donors in the
organism are hydrogen atoms of organic molecules
(e.g. glucose, fatty acids).
The hydrogen atom consists of an H+ and an e-.
The most important electron receivers are the
oxygen molecule of air (O2).
Mechanism of Biological Oxidations
Biological oxidizations are the transport of H ions and electrons
in these organic materials to oxygen. The reactions are formed
in steps rather than in a single reaction. In these steps, H ions
and electrons in organic materials are transported by oxidation-
reduction enzymes (redox enzymes).
Reducing equivalent refers to any of a number of chemical
species which transfer the equivalent of one electron in redox
reactions. Redox enzymes are essential for this transfer. They
are transported either directly or indirectly to the oxygen.
Mechanism of Biological Oxidations
Direct biologic oxidations in body occur in very small
amounts. The enzymes involved in this case are
Oxidase.
Indirect biologic oxidations in body occurs in great
amounts. dehydrogenases.
Mechanism of Biological Oxidations
Indirect Biologic Oxidations • In this type of biological oxidation, H ions and electrons are
taken from the organic molecules through enzymes and
transported as a series of enzymes as oxygen.
• In this case, dehydrogenases are called respiratory enzymes.
The active moieties (i.e. the moieties carrying hydrogen and
electrons from organic molecules) carrying the reduction
residues of these enzymes are the coenzymes and the
coenzymes are grouped into four groups according to their
active groups.
Mechanism of Biological Oxidations
1. PYRIDINE NUCLEOTIDE ENZYMES• The effective group is nicotinic acid amide. The full name of
the coenzyme is nicotinamide adenine dinucleotide (NAD). There are 2 phosphoric acids in the structure. In the third entry, NADP+ (nicotinamide adenine dinucleotidephosphate) occurs.
• NAD and NADP+ are reduced by receiving electrons and H ions, becoming NADH+H+ and NADPH.
• Enzymes with coenzyme NAD are particularly involved in carbohydrate metabolism, metabolic pathways such as glycolysis and TCA cycle, and in the mitochondrial respiratory chain.
Mechanism of Biological Oxidations
2. FLAVIN CONTAINING ENZYMES • The effective group is riboflavin (Vitamin B2), its dimethyl-
isoalloxazine group. The full name is flavin adenine
dinucleotide (FAD).
• Reduced state is FADH2. FAD is tightly bound to a specific
apoenzymes.
• In the respiratory chain, the electrons and hydrogen taken
from pyridine enzymes and organic substances are
transferred to the quinone enzymes (Q) by FAD.
Mechanism of Biological Oxidations
3. ENZYMES WITH QUINONE (COENZYME Q10)• Effective group is quinone. It carries 10 isoprene as a
side chain. It is reduced to hydroquinone after
gaining 2H+ and 2e-.
• There is a close relationship with cytochromes
involved in the biological oxidation chain. 2H+ and 2e-
from Flavin containing enzymes causes reduction of
its and these are given to cytochromes (iron
containing enzymes).
Mechanism of Biological Oxidations
4.ENZYMES CONTAINING IRON• Active group is iron (Fe). It is located in porphine
skeleton. Thereby forming a coenzyme.
• These coenzymes, which are found in porphyrin
structures, bind very tightly to various specific
proteins, bringing up various ferric enzymes. These
enzymes are mainly cytochromes and cytochrome
oxidases.
Mechanism of Biological Oxidations
• This coenzyme function is based on the fact that
only the electrons exchange and give rise to
changes in the iron valence.
• Trivalent iron is reduced to divalent iron. There
are three types of cytochromes; b1, c1 and c
cytochromes.
• They transfer the electrons they receive from
Koenzim Q to one another.
Mechanism of Biological Oxidations
The electron donor is oxidized
and acceptor is reduced. Reduced
cytochrome c gives its electrons
to cytochrome oxidases and is
self-oxidized again.
There are two types of
cytochrome oxidases; Cytochrome
a and cytochrome a3.
Mechanism of Biological Oxidations
Cytochrome c
Cytochrome oxidase a3 takes electrons from the
cytochrome c and reduced.
Reduced cytochrome oxidase a3 gives electrons to O2
and turns it to oxygen ions.
The oxygen ion also reacts with the two hydrogen atoms
in the environment, so that water is synthesized.
The synthesis of endogenous water in the organism
occurs in this way.
Mechanism of Biological Oxidations
Much of the biological oxidation occurs when multiple oxidation-
reduction events complement each other and are arranged as
rings of a chain.
At the end of this chain, there is an oxidized substance formed
by the direct effect of a special dehydrogenase enzyme by
activating the hydrogen from the organic substances and a
molecular oxygen at the other end.
Between the two ends a special alignment of hydrogen and
electron acceptor and carrier enzymes is observed. This is called
the electron transport chain or the respiratory chain. This
chain can start from the NAD as well as from the FAD.
The function of the Respiratory Chain
Video Source: Youtube
Overall energy is revealed at the end of oxidation. The chemical
entering the reaction goes down to a level lower than the high
energy level in the system. The same phenomenon is seen in the
respiratory chain. During the 2 H + and 2 e-transport, there is
sufficient energy production to form a high-energy bond.
The energy released is moved adenosine diphosphate 'e (ADP)
with an inorganic phosphate. ADP uses the energy and phosphate
linking constitute high energy adenosine triphosphate (ATP).
The amount of energy and production place in the respiratory chain
If chain starts from a dehydrogenase with
NAD and is oxidased, 3 mol ATP is
synthesized.
If chain starts from a dehydrogenase with
FAD and is oxidased, 2 mol ATP is
synthesized.
The amount of energy and formation place in the respiratory chain
One of the events that continue to occur in organism is
biological oxidations.
These events provide the necessary energy for
endergonic chemical reactions occurring in the body, as
well as the emergence of many new substances
necessary for the body during oxidation and degradation
of a substance.
Importance of Biological Oxidation
700 kcal for 1 mole of glucose in biological oxidation
occurs. 1 mol ATP stores 7-8 kcal.
The energy stored in the form of ATP,• Is used in the formation and maintenance of body
temperature.
• Provides to maintain peptide bonds, glycoside bond and many
reaction events.
• Is used to maintain active contraction of the muscles and cell
membrane permeability (active transport) and secretion
events.
Importance of Biological Oxidation
A metabolic pathway is a linked series of chemical
reactions occurring within a cell.
Some metabolic pathways flow in a 'cycle' wherein each
component of the cycle is a substrate for the
subsequent reaction in the cycle. The sequence of chain
reactions starting from a basic substance and returning
to that basic substance at the end of ongoing reactions
is called the metabolic cycle or reaction cycle.• For example: TCA cycle or Krebs Cycle
The reaction cycles of metabolism
TCA Cycleor
Krebs Cycleor
Citric acid cycle
Nucleus• Transfer and replication of hereditary molecules (DNA and
RNA), hydrolysis and synthesis of nucleic acids, proteins
(transcription).
Mitocondria• Biological oxidations, TCA cycle, ATP synthesis.
Ribosomes• Protein biosynthesis (translation).
Locations of Metabolic Reactions in the Cell
Endoplasmic Reticulums• Folding and transport proteins.
Lysosomes• Hydrolysis of nucleic acids and proteins proteinase. It contains
many proteolytic enzymes such as RNase, phosphatases,
glycosidases.
Cytoplasm• Glycolysis, destruction of proteins, destruction of fat, glycogen
breakdown, biosynthesis of fatty acids.
Locations of Metabolic Reactions in the Cell
Question 1
Answer: a
........... İs a reaction in which two or more molecules combine to form a larger molecule, with the simultaneous loss of a small molecule such as water.
a. Condensation
b. Hydrolysis
c. Oxidation
d. Dehydrogenation
e. Reduction
Question 2
Answer: d
Which of the following molecules carry multiple
phosphate residue?
a. PEP
b. G-6-P
c. Creatin Phosphate
d. ATP
e. AMP
Question 3
Answer: c
Which of the following is not a coenzyme of respiratory
chain?
a. NAD
b. FAD
c. Phosphofructokinase
d. Cytocrom a
e. Q10
Any Questions?
Ası T. 1999. Tablolarla Biyokimya II. Nobel Tıp Kitapları Dağıtımı
Sözbilir Bayşu N, Bayşu N. 2008. Biyokimya. Güneş Kitabevi
References
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