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Carbohydrates
metabolism
Glycolysis, cellular respiration and
fermentation
Living organisms transform biomolecules that are present in
nutrients in order to produce energy and precursors for the
synthesis of macromolecules. This transformation process is
called metabolism.
Metabolic pathways can be catabolic (they degrade
molecules) and anabolic (they synthesize molecules).
What is the metabolism?
https://www.youtube.com/watch?v=ZkqEno1r2jk
What is Aerobic
Respiration?
Photosynthesis
Photosynthesis and
cellular respiration
https://www.youtube.com/watch?v=q-fKQuZ8dco
Watch the video
1. What is mitochondrion?
2. Do you remember its function?
Mitochondria
Mitochondrion
1. Where does glycolysis take place?
2. What is glycolysis?
3. Could you describe the steps of glycolysis?
Glycolysis
Glycolysis
Glycolysis is the catabolic pathway that leads to the
breaking down of glucose (6 atoms of C) to pyruvate (3
atoms of C).
Glycolysis
Glycolysis: a closer look
Glycolysis is divided into two phases:
• preparatory phase – 2 ATP molecules are used to
produce glyceraldehyde 3-phosphate;
• pay-off phase – production of 4 ATP molecules
and 2 pyruvate molecules.
Glycolysis
Glycolysis
• Glucose (6C)
• 2 ATP (as activation energy), 4 ADP, 2 NAD+
• Enzymes
Requirements for
Glycolysis
• 2 of Pyruvate (ionized form of Pyruvic Acid) (3C)
• 2 ADP, 4 ATP, 2 NADH
The Products of
Glycolysis
Glycolysis:
Nicotinamide Adenine Dinucleotide Plus, a
redox coenzyme and energy carrier.
Glycolysis
Glycolysis
Glucose is phosphorilated by
ATP, then rearranged by an
isomerase enzyme, then
phosphorilated again by ATP.
The fructose 1,6-bisphophate
produced is then broken into two
molecules of G3P,
(glyceraldehyde 3-phosphate).
energy investment phase
Each G3P is oxidized by
NAD+, so 2 NADH are
produced. After, part of the
energy of the intermediate
organic molecules is
captured inside 2
molecules of ATP (total: 4
ATP).
In the end, two molecule of
pyruvate are left.
energy payoff phase
To sum up…
Puzzle
Solution
In aerobic conditions, pyruvate (3 C) is transferred
inside the mitochondria, where the pyruvate
dehydrogenase complex transforms it into acetylCoA.
Pyruvate + NAD+ + CoA
i
Acetyl-CoA + CO2 + NADH + H+
From pyruvate to acetyl-CoA
https://www.youtube.com/watch?v=q-fKQuZ8dco
From pyruvate to acetyl-CoA
Coenzyme A (CoA)
Inside the mitochondrion (before the citric acid cycle can begin), pyruvate
(3C) must be decarboxylated into acetate (2C), then oxidized and joined to a
molecule of Coenzyme A, and so converted to acetyl CoA, which links the
cycle to glycolysis.
During the transformation process of pyruvate into acetyl CoA , a molecule of
CO2 is released and a molecule of NADH is produced.
From pyruvate to acetyl-CoA
Acetyl CoA
Acetyl-CoA enters
the Krebs cycle (or
citric acid cycle)
where, in a series of
steps, the molecule
isoxidized to CO2
while at the same
time reducing NAD
to NADH.
Krebs cycle
https://www.youtube.com/watch?v=q-fKQuZ8dco
The citric acid cycle, also called the Krebs cycle, oxidizes
organic fuel derived from pyruvate, generating , for every
turn:
 1 ATP
 3 NADH
 1 FADH2
Krebs cycle
FAD is the oxidized form of another redox coenzyme.
FAD can accepts two electrons and two protons to become FADH2, the
reduced form.
FAD and FADH2
The citric
acid cycle
has eight
steps, each
catalyzed by
a specific
enzyme
Krebs cycle
• Acetyl CoA (2C)
• 1 ADP
• 3 NADP+
• 1 FAD
into the Krebs cycle
• 2 CO2
• 1 ATP
• 3 NAD+
• 1 FADH2
Out of the Krebs cycle
NADH and FADH2 transfer electrons to a system of
proteins into the internal membranes of mitochondria.
These proteins constitute the electron transport
chain or respiratory chain.
Electron transport chain
https://www.youtube.com/watch?v=q-fKQuZ8dco
Electron transport chain
• The respiratory chain is a sequence of redox
reactions, during which proteins in different
complexes accept electrons and donate them
immediately to the next complex.
• Oxygen is the final electron acceptor.
• The respiratory chain does not directly generate
ATP, but energy in the form of proton motive force,
which is necessary for oxidative phosphorylation
Function of the electron
transport chain
Oxydation of NADH
+ H+ frees 2
electrons and 2
protons (H+).
Electrons enter the
transport chain,
transferred from
complex I to
complex IV and to
oxygen.
With each redox
reaction, new
protons are
generated, which are
pumped across the
mitochondrial
membrane into the
intermembrane
space.
The formation of a
proton gradient
High concentrations of
H+ at one side of the
membrane create an
electrochemical
gradient in which
protons flow from the
compartment at higher
concentration to the
compartment at lower
concentration.
The flux of protons
pass through the F0
region of ATP
synthase which
activates the F1
subunit, where the
synthesis of ATP takes
place.
Proton gradient
and ATP synthase
INTERMEMBRANE SPACE
The proton concentration
gradient and electric
charge difference
constitute a source of
potential energy called
the proton-motive force.
Coupling of the protonmotive force and ATP
synthesis is called
chemiosmosis or
chemiosmotic
mechanism.
Proton gradient and
ATP synthase
H+
Stator
Rotor
Internal
rod
Catalytic
knob
ADP
+
P
i
ATP
MITOCHONDRIAL MATRIX
The respiratory chain and ATP synthase produce
ATP by a chemiosmotic mechanism
Video Zanichelli su pc
The respiratory chain and
the oxidative
phosphorilation
Chemiosmosis
Chemiosmosis
Chemiosmosis
Chemiosmosis
Chemiosmosis
Chemiosmosis
Chemiosmosis
https://www.youtube.com/watch?v=HZtXLhm7ISA
Anaerobic conditions:
fermentation
• In the presence of O2, NADH and pyruvate are used to
generate ATP in respiration.
• In the absence of oxygen, carbohydrate metabolism
does not follow the same pathway: pyruvate goes
through alcoholic fermentation or lactic fermentation.
• Fermentation turns NADH and pyruvate produced in the
glycolysis phase into NAD+ and various small molecules
depending on the type of fermentation.
Anaerobic conditions:
fermentation
• it takes place in the muscle tissue and its product is lactic
acid
Lactic fermentation
In lactic fermentation, pyruvate produced by glycolysis is reduced to lactic acid. The
necessary electrons are provided by NADH + H+, generated during the pay-off phase.
Glycolysis and Lactic acid
fermentation
• it takes place primarily in yeast and its product is ethyl
alcohol.
Alcoholic fermentation
Pyruvate
decarboxylase
Alcohol dehydrogenase
In some yeasts, alcoholic fermentation takes place: pyruvate
goes through a decarboxylation and is converted to
acetaldehyde, then reduced to ethanol thanks to NADH + H+.
Glycolysis and Alcoholic
fermentation
Cellular respiration
yields more energy than
fermentation