I've read the threads outlining ATP synthesis, I've read Nature of Biology outlining it and I have studied the Biozone explanation but this biological process still eludes my understanding in how it all fits together. 
Could someone be kind enough to outline the whole process tracking the glucose molecule from the beginning right to the very end and how ATP is produced and consumed throughout the process as well as the meaning of each specific process at each stage (glycolysis, link reaction, krebs, electron transport).
I don't care if it goes outside the VCE course because I do not want to rote learn just the definitions for Krebs cycle etc. What I need to understand to learn it, is how it all fits together from beginning to end, because right now I am just confused as hell.
I even had a freaking tutor session once off and he was completely useless and just scratched the surface.
Thanks a ton in advance.
Below is the depth I learnt it in (from my notes, actually). I'd like to stress that this is
still just a simplification. However, this depth is still beyond the scope of 3/4 Bio.
There isn't much point learning more than what I put for Kreb's or Glycolysis, as at that point you're just rote learning enzymes and intermediate compounds.
Aerobic Cellular Respiration• Cellular respiration involves the breakdown of glucose into ATP (chemical energy in glucose is converted into immediately usable energy of ATP)
• One of two types of respiration. It requires oxygen. The other type is anaerobic respiration, which does not require oxygen.
• It is an exergonic, catabolic reaction (CATS EXPIRE: catabolic, exergonic, respire)
• Balanced equation: C6H12O6 + 6O2 --> 6CO2 + 6H2O
• Word equation: glucose + oxygen gas --> carbon dioxide + water
• Occurs in the mitochondria:
• It has two membranes - the outer membrane and the high folded inner membrane. A mitochondria can be easily recognised by this folded inner membrane. The infoldings in this inner membrane are known as the cristae.
• The intracellular space bordered by the inner membrane is known as the mitochondrial matrix (or simply matrix).
• The mitochondria has its own ribosomes and its own circular DNA (mtDNA), similar to prokaryotic DNA. This DNA is passed maternally.
• This is evidence for the fact that they once existed as separated prokaryotic organisms (see the endosymbiotic theory)
• It is slower than anaerobic respiration, but more efficient (more ATPs per glucose molecule generated)
• It is a continuous, sustained reaction, whereas anaerobic respiration lasts for short bursts of time.
• Occurs in three stages:
Glycolysis, Krebs Cycle and
Electron Transport. Only the last two are exclusive to aerobic respiration: glycolysis also occurs with anaerobic respiration
Glycolysis• Inputs: glucose, ADP+Pi, NAD+
• Outputs: 2 pyruvate, 2 ATP, 2NADH
• Where: cytosol
• What happens: a glucose molecule is broken down into two pyruvate molecules via a series of intermediate reactions.
• The process actually requires an input of 2 ATPs, but generates 4 ATPs, resulting in a net gain of 2 ATPs (probably not that relevant to the course). High energy electron carrier NADH is also produced.
Krebs Cycle/ Citric Acid Cycle• Inputs: pyruvate, ADP+Pi, NAD+, FAD
• Outputs: NADH, FADH2,1 ATP, 3 CO2 (per pyruvate. Remember there are two pyruvates per glucose)
• Where: mitrochondrial matrix
• What happens: pyruvate is, via a series of intermediate reactions, converted into 3 carbon dioxide molecules, 2 ATP and high energy electron carriers for use in electron transport.
• Pyruvate is first broken down into a two carbon compound (producing one CO2 molecule) which joins with coenzyme A to form Acetyl CoA (note that this is technically not part of the Krebs Cycle). Acetyl CoA enters the Krebs Cycle and undergoes a series of reactions, producing the high energy electron carriers NADH and FADH2 as well as ATP. This process produces 2 CO2 molecules (again, per pyruvate).
• Why is it a cycle? This isn't too relevant to 3/4 Biology, but it is cyclic in nature because the Acetyl CoA joins with a 4 carbon compound known as oxaloacetate. The resulting substance undergoes the Krebs Cycle, which ends up regenerating oxaloacetate for future use (on top of the other products.)
Electron Transport Chain• Inputs: NADH, FADH2, ADP+Pi, O2
• Outputs: Water, NAD+, FAD, 32-34 ATPs
• Where: cristae of the mitochondria
• What happens: the high energy electrons from the previous stages undergo a series of reactions, releasing the energy that drives ATP synthesis.
• The high energy electron carriers, NADH and FADH2, carry the high energy electrons to the electron transport chain, a series of reactions that the electrons undergo (redox reactions), losing energy in each reaction. It (this electron transport chain) is facilitated by cytochrome protein complexes. The energy produced is used to drive the synthesis of ATP via the protein complex ATP Synthase (
NB. this is a simplification. The following is for your interest only: the electron transport chain actually involves protons being pumped out into the intermembrane space between the cristae and the outer membrane. This causes a H+ buildup in the intermembrane space, meaning the H+ ions want to move back into the matrix (the H+ gradient is known as a proton-motive force). The only pathway for them to move back is ATP Synthase, and as they move back it drives the synthesis of ATP.)
• The electrons are finally accepted by oxygen, which becomes reduced (remember reduction = gaining electrons) to water.
• What causes the difference in ATP production in the electron transport chain? Some cells require the generation of more ATP, specifically liver and muscle cells because they are more energy intensive.
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