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Dr. Jagdish kaur
P.G.G.C., Sector 11, Chandigarh
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Carbohydrate metabolism denotes the
various biochemical processes responsible for
the formation, breakdown and
interconversion
of carbohydrates in living organisms.
The most important carbohydrate is glucose,
a simple sugar (monosaccharide) that is
metabolized by nearly all known organisms.
Metabolic pathways
Carbon fixation, or photosynthesis, in which CO2 is
reduced to carbohydrate.
Glycolysis - the oxidation metabolism
of glucose molecules to obtain ATP and pyruvate.
Pyruvate from glycolysis enters the Krebs cycle, also
known as the citric acid cycle, in aerobic
organisms after moving through pyruvate
dehydrogenase complex.
The pentose phosphate pathway, which acts in the
conversion of hexoses into pentoses and
in NADPH regeneration. NADPH is an essential
antioxidant in cells which prevents oxidative damage
and acts as precursor for production of many
biomolecules.
Glycogenesis - the conversion of excess glucose
into glycogen as a cellular storage mechanism; this
prevents excessive osmotic pressure buildup inside the
cell.
Glycogenolysis - the breakdown of glycogen into
glucose, which provides a glucose supply for glucosedependent tissues.
Gluconeogenesis - de novo synthesis of glucose
molecules from simple organic compounds. An
example in humans is the conversion of a few amino
acids in cellular protein to glucose.
Metabolic use of glucose is highly important as an
energy source for muscle cells and in the brain, and red
blood cells.
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It occurs in cytoplasm.
Anaerobic process.
Discovered by:-Gustav Embden , Otto
Meyerhoff and J. Parnas.
Also known as EMP pathway.
Only process available in all organism.
Occurs in two phases:- 1st is ENERGY
SPENDING PHASE for activation of glucose.
2nd is ENERGY RELEASING PHASE.
 Regulatory enzyme of glycolysis is
PHOSPHOFRUCTOKINASE.
 All enzyme of glycolysis require Mg2+
cofactor.
 RBCs and muscles gets energy by
glycolysis.
 It is a Ten step mediated process.
 End product is two molecule of 3-C
PYRUVATE.
 Depend on cell’s need: It occurs in three Major ways:1.
2.
3.
Aerobic Respiration.
Anaerobic respiration.
Lactic acid fermentation.
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It is a linking reaction between glycolysis and
citric acid cycle.
It is also known as transition reaction or
Gateway step.
It occurs in the presence of enzyme pyruvate
dehydrogenase.
Pyruvate+NAD+ + Co-A======Acetyl CoA+NADH+H+ CO2.
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If oxygen is available each 3-C pyruvate
molecule enters in mitochondrial matrix.
Now , oxidation will complete in two
phases:1. Formation of Acetyl Co-A (Oxidative
decarboxylation.)
2. Kreb’s cycle.
It occurs in mitochondrion.
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The citric acid cycle – also known as
the tricarboxylic acid (TCA) cycle or
the Krebs cycle – is a series of chemical
reactions used by all aerobic organisms to
generate energy through
the oxidation of acetate derived from
carbohydrates, fats and proteins into carb
on dioxide and chemical energy in the
form of adenosine triphosphate(ATP).
The citric acid cycle begins with the transfer of a twocarbon acetyl group from acetyl-CoA to the four-carbon
acceptor compound (oxaloacetate) to form a six-carbon
compound (citrate).
 The citrate then goes through a series of chemical
transformations, losing two carboxyl groups as CO2. The
carbons lost as CO2 originate from what was oxaloacetate,
not directly from acetyl-CoA. The carbons donated by
acetyl-CoA become part of the oxaloacetate carbon
backbone after the first turn of the citric acid cycle. Loss of
the acetyl-CoA-donated carbons as CO2 requires several
turns of the citric acid cycle. However, because of the role
of the citric acid cycle in anabolism, they might not be lost,
since many TCA cycle intermediates are also used as
precursors for the biosynthesis of other molecules.
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Most of the energy made available by the
oxidative steps of the cycle is transferred as
energy-rich electrons to NAD+, forming NADH.
For each acetyl group that enters the citric acid
cycle, three molecules of NADH are produced.
 Electrons are also transferred to the electron
acceptor Q, forming QH2.
 At the end of each cycle, the four-carbon
oxaloacetate has been regenerated, and the
cycle continues.
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The electron transport chain (ETC) uses the NADH
and FADH2 produced by the Krebs cycle to generate
ATP. Electrons from NADH and FADH2 are transferred
through protein complexes embedded in the inner
mitochondrial membrane by a series of enzymatic
reactions. The electron transport chain consists of a
series of four enzyme complexes (Complex I –
Complex IV) and two coenzymes (ubiquinone and
Cytochrome c), which act as electron carriers and
proton pumps used to transfer H+ ions into the space
between the inner and outer mitochondrial
membranes.
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The ETC couples the transfer of electrons between a donor (like
NADH) and an electron acceptor (like O2) with the transfer of
protons (H+ ions) across the inner mitochondrial membrane,
enabling the process of oxidative phosphorylation. In the
presence of oxygen, energy is passed, stepwise, through the
electron carriers to collect gradually the energy needed to attach a
phosphate to ADP and produce ATP. The role of molecular oxygen,
O2, is as the terminal electron acceptor for the ETC. This means
that once the electrons have passed through the entire ETC, they
must be passed to another, separate molecule. These electrons,
O2, and H+ ions from the matrix combine to form new water
molecules. This is the basis for your need to breathe in oxygen.
Without oxygen, electron flow through the ETC ceases
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Embedded in the inner mitochondrial
membrane.
It is a turbine that is powered by the flow of
H+ ions across the inner membrane down a
gradient and into the mitochondrial matrix.
As the H+ ions traverse the complex, the shaft
of the complex rotates. This rotation enables
other portions of ATP synthase to encourage
ADP and Pi to create ATP.
 Phenomenon of transformation
excess of glucose of blood
plasma into glycogen.
 Chiefly occurs in liver and
muscles.
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Hexose Monophosphate shunt.