Detailed Analysis of Aerobic Respiration and ATP Production in Biology

This report provides a comprehensive overview of aerobic respiration, the primary process for energy production in the human organism. It elucidates the process from biochemical and cellular perspectives to anatomical and physiological levels. The report details the four major steps: glycolysis, the formation of Acetyl Co-A, the citric acid cycle, and the electron transport chain (ETC). Glycolysis, occurring in the cytosol, breaks down glucose to produce ATP and NADH. The formation of Acetyl Co-A bridges glycolysis and the citric acid cycle. The citric acid cycle, or Krebs cycle, generates ATP, NADH, and FADH2. Finally, the ETC utilizes NADH and FADH2 to produce a significant amount of ATP. The report also includes figures illustrating the steps and energy conversions within each stage.

Running head: MOLECULAR AND CELLULAR BIOLOGY
Topic: MOLECULAR AND CELLULAR BIOLOGY
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1MOLECULAR AND CELLULAR BIOLOGY
Describe the process of energy production (the formation of ATP) by aerobic
respiration from biochemical and cellular levels to anatomical and physiological levels
within the human organism.
Cellular respiration is one of the most important metabolic pathways in the cellular
system. Aerobic respiration is the most important biological process which utilizes energy
form the glucose as well as other organic compounds. The ultimate aim of the respiration
process is the creation of ATP or Adenosine Triphosphate (Hill, 2014). The four major steps
including the various steps are
 Glycolysis
 Acetyl Co-A formation
 Citric Acid cycle
 ETC or Electron Transport Cycle
Fig 1: The breakdown of food into various components and detailed energy production
process both aerobic and anaerobic respiration

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Glycolysis
The primary step of the process of aerobic respiration involves glycolysis. The
process usually occurs in the location of cytosol of the cell. Glycolysis involves glucose
breakdwon which is mainly separated into 2 ATP as well as 2 NAPDH molecules. It is used
inclusive of the process of the aerobic respiration. There are total nine steps of glycolysis for
the conversion which is inclusive of glucose into pyruvate (Lenzen 2014).
The first step phosphorylation takes place though addition of phosphate groups to
molecule usually taken from ATP. Thus after the first step, 1 molecule of ATP has been
usually consumed. The reaction catalyzed by hexokinase involves Mg2+ ions for shielding the
negative charges. The second step involves the conversion which is inclusive of glucose 6
phosphate to fructose 6 phosphate through phosphoglucose isomerase. This is usually an
isomerization reaction. In the third step there is conversion of fructose 6 phosphate to
fructose 1, 6 bisphosphate through ATP utilization. It is added to the fructose 6 phosphate
molecule. This equation is catalyzed by phosphofructokinase. The fourth step is the final step
of the first stage of glycolysis which involves the cleavage of the molecule for fructose
bisphosphate for yielding 2 3 carbon molecules. One is glyceraldehyde 3 phosphate as well as
the other is dihydroxy acetone phosphate (Heerden et al. 2015).
The sixth step involves the dehydrogenation of the glyceraldehyde 3 phosphate
dehydrogenase molecule and addition of an inorganic phosphate causing the formation of 1, 3
bisphospho glycerate. In the next step there is transfer of the phosphate group’s form from 1,
3 bisphos-phoglycerate to ADP for formation of ATP as well as 3 phosphoglycerate through
phosphoglycertae kinase. Thus in this step there is synthesis of two molecule s for ATP.
Thus the net ATP balance is 0. The last three steps are inclusive of relocation of phosphate
form 3 phosphoglyceratae to 2 phosphoglycerate through transfer from the 3rd carbon to the
second carbon. Followed by conversion of 2 phosphoglycertae to phosphoenol pyruvate

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through a dehydration reaction. Specificity of the enzyme pocket allows the transition
through a series of reaction. In the final step there is conversion of posphoenolpyruvate to
pyruvate through pyruvate kinase (Hu et al. 2016). Thus in the ultimate step the energy
transfer and balance sheet is as follows.
Steps 1, 3 = -2 ATP
Steps 7, 10= +4 ATP
Net ATP produced = 2

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Fig 2: The detailed stepwise glycolysis process divided into two phases

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Formation of Acetyl Co-A
Fig 3: The process of Acetyl-CoA formation
The following step including the process of aerobic respiration is inclusive of the
formation of acetyl Coenzyme A. In the given state, it is brought in mitochondria where
oxidation take place leading to the creating of 2 carbonacetyl group. This step is followed to
the binding to the coenzyme A which forms acetyl coenzyme A. Then the acetyl coenzyme A
is usually brought back in to the mitochondria for the use in the next step (Can et al. 2014).
Citric acid cycle
In the 3rd step of the aerobic respiration it is usually known as the Krebs’s cycle, citric
acid cycle, and the tri-carboxylic acid cycle. There are usually two turns of thee citric acid
cycle which are required for breaking down acetyl coenzyme A from single molecule of
glucose. The formation of additional two cycle ATP molecules along with the formation of
six NADH along with two FADH molecules which are used later (Akram 2014).
The first reaction involved in the tricarboxylic acid cycle has been the formation of
Citrate. Thus in the 1st reaction, there is formation of citrate where there is condensation of
the acetyl CoA along with the oxaloacetate for ultimately forming citrate which is catalyzed
by the citrate synthase. The second reaction is the formation of isocitrate through
rearrangement or formation of an isomeric form through the enzyme aconitase. This reaction

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is shown by the removal of water molecule from citric acid this conversion of the OH group
yields isocitrate though transformation. The 3rd step is the oxidation of the isocitrate to the
molecule of Alpha ketoglutarate through the help of isocitrate dehydrogenase catalyzing the
oxidative decarboxylation of the isocitrate to the alpha ketoglutarate. The fourth step is
shown by the oxidation of the alpha ketoglutarate to the succinyyl CoA where the alpha
ketoglutarate is oxidized to form 4 carbon succinyyl CoA though the catalysis of the reaction
by alpha ketoglutarate dehydrogenase. The next step is shown by the conversion of the
succinyyl CoA to succinate where CoA removed from the molecule of succinyyl CoA to the
molecule of succinate. Thus the energy which is released is use for the formation of
guanosine triphosphate through substrate level phosphorylation where the GTP is used for
making ATP where the reaction is catalyzed by the citric acid cycle. The next step involves
reversible hydration of fumarate to L malate which is catalyzed by fumarase also known as
fumarase hydratase. The last step is an oxidation of malate to Oxaloacetate which is oxidized
by malate dehydrogenase where there is reduction of NADH to NADH and H+ (Czibik
2014).
The energy balance of the reaction is
Total ATP = 12 ATP
3 NAD+ = 9 ATP
1 FAD = 2 ATP
1 ATP = 1 ATP

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Fig 4: The detailed stepwise tricarboxylic cycle with energy conversion
Electron Transport Cycle
The last step of the aerobic respiration process known as electronic transport chain.
Here NADH as well as FADH usually donates various electrons for the production of large
amounts of ATP. Thus through the process, one molecule of glucose leads to the formation of
a total number of 34 ATP molecules (Titov et al. 2016).
Thus the process of electron transport chain (ETC) usually occurs among the
mitochondria. In the inner mitochondrial membrane electrons from the NADH along with
FADH2 usually pass through the ETC to the oxygen molecule which is usually reduced to
water molecule. There is an enzymatic series of electron acceptors along with donors. The
electron donor pass the electron to a more electronegative acceptor where there is donation of
the electrons. There 4 membrane bound complexes which has been identified in
mitochondria. Usually, each complex is extremely trans-membrane structure which is

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embedded in the membrane. Three among them are proton pumps. Various structure are
usually connected through the help of lipid soluble carriers along with water soluble carriers
(Lets and Sazanov 2016). Thus the final reaction of the process is
NADH+H+ → Complex I → Q → Complex III → cytochrome c → Complex IV → H2O
↑
Complex II
↑
Succinate
Fig 5: The stepwise process of electron transport chain

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References
Can, M., Armstrong, F.A. and Ragsdale, S.W., 2014. Structure, function, and mechanism of
the nickel metalloenzymes, CO dehydrogenase, and acetyl-CoA synthase. Chemical
reviews, 114(8), pp.4149-4174.
Czibik, G., Steeples, V., Yavari, A. and Ashrafian, H., 2014. Citric acid cycle intermediates
in cardioprotection. Circulation: Cardiovascular Genetics, 7(5), pp.711-719.
Hill, G.E., 2014. Cellular respiration: the nexus of stress, condition, and
ornamentation. Integrative and comparative biology, 54(4), pp.645-657.
Hu, H., Juvekar, A., Lyssiotis, C.A., Lien, E.C., Albeck, J.G., Oh, D., Varma, G., Hung, Y.P.,
Ullas, S., Lauring, J. and Seth, P., 2016. Phosphoinositide 3-kinase regulates glycolysis
through mobilization of aldolase from the actin cytoskeleton. Cell, 164(3), pp.433-446.
Lenzen, S., 2014. A fresh view of glycolysis and glucokinase regulation: history and current
status. Journal of Biological Chemistry, 289(18), pp.12189-12194.
Letts, J.A. and Sazanov, L.A., 2017. Clarifying the supercomplex: the higher-order
organization of the mitochondrial electron transport chain. Nature structural & molecular
biology, 24(10), p.800.
Titov, D.V., Cracan, V., Goodman, R.P., Peng, J., Grabarek, Z. and Mootha, V.K., 2016.
Complementation of mitochondrial electron transport chain by manipulation of the
NAD+/NADH ratio. Science, 352(6282), pp.231-235.
van Heerden, J.H., Wortel, M.T., Bruggeman, F.J., Heijnen, J.J., Bollen, Y.J., Planqué, R.,
Hulshof, J., O’Toole, T.G., Wahl, S.A. and Teusink, B., 2014. Lost in transition: start-up of
glycolysis yields subpopulations of nongrowing cells. Science, 343(6174), p.124511