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Energy production for cellular events
Fabinyi Bianka
2016.09.22.
The main energy suppliers of a cell are the mitochondria. They have an outer and an inner membrane
that are separated by the intermembrane space and surround the matrix. The inner membrane folds
in several times, creating cristae that expands the surface. The outer membrane is more permeable,
allows ions and molecules under 5000 Da to pass through Porin channels. The inner membrane
contains enzyme complexes, that are part of the oxidative phosphorylation, and transport proteins. It
has a restricted permeability, highly regulated, that doesn’t even allow ions to pass through. The matrix
contains proteins, enzymes and mitochondrial DNA. The citric acid cycle, the beta-oxidation and other
processes are also placed here.
Cells intakes multiple kind of possible fuels for energy, that has different routes to become ATP. The
average human needs 160 g of glucose a day, of which 120 g used by the brain. Glycolysis takes place
in the cytosol, processes glucose and results in the following equation in aerobic conditions:
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glucose + 2Pi + 2ADP + 2NAD+ -> 2pyruvate + 2ATP + 2H2O + 2NADH + 2H+
In anaerobic conditions:
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glucose + 2Pi + 2ADP -> 2lactate + 2ATP + 2H2O
The difference is 34 ATPs, because in anaerobic conditions from pyruvate an enzyme creates lactate,
that can’t be processed for further ATPs, but can be used in the Cori cycle. The Cori cycle can transform
the lactate back to glucose in exchange for ATPs.
The Citric acid cycle processes the created Acetyl-CoA, that is previously created from different
carbohydrates, proteins and fats.
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acetyl-CoA + 3NAD+ + FAD + GDP + Pi + 2H2O -> 2CO2 + 3NADH + 3H+ +FADH2 + GTP + CoA
It not just generates ATP but also provides precursor for creating amino acids. As glycolysis, CAC also
regulated in several ways for energy preserving. The created NADHs transfers electrons to the electron
transport chain.
Oxidative phosphorylation uses the pH gradient and electrical potential that is created by the proton
pumps, to create ATP. This is why the impermeability of inner membrane is so important. The enzyme
for this is the ATP synthase and the three complexes of the electron transport chain (I., III., IV.).
Complex III. and IV. are cytochromes, that have a heme group in their structure. Cytochrome c is a
electron carrier between Complex III. and IV..
Sources:
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https://biochemistry3rst.files.wordpress.com/2014/03/glycolysis-cycle-3.jpg
http://www.humpath.com/IMG/jpg_citric_acid_cycle_noi_wkp_0807_a.jpg
https://fastly.kastatic.org/ka-perseus-images/fe1296eb6182efc88ea25a88f0a02638a7339410.png
https://upload.wikimedia.org/wikipedia/commons/0/07/Cytochrome_c.png
http://www.livescience.com/images/i/000/075/701/i02/mitochondrion-diagram.jpg?1430372329?interpolation=lanczos-none&downsize=640:*
https://en.wikipedia.org/wiki/Mitochondrial_matrix
https://en.wikipedia.org/wiki/Cori_cycle
Ádám Veronika: Orvosi Biokémia
Darvas Zsuzsa: Sejtbiológia
https://en.wikipedia.org/wiki/Citric_acid_cycle
https://en.wikipedia.org/wiki/Glycolysis