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(AQA A2 Biology)

Mark Gavartin

on 7 January 2013

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Transcript of Respiration

Link Reaction Krebs Cycle The link reaction takes place only in the presence of oxygen. The link reaction moves the pyruvate into the mitochondrion from the cytoplasm. This is irreversible. This is where the bulk of the substrate level phosphorylation occurs. The cycle occurs in the matrix of the mitochondrion Respiration This is the controlled oxidation of monosaccharides to release chemical energy in the form of ATP, which takes place in all living cells.

C6H12O6 + 6O2 6CO2 + 6H2O + energy There are a number of inaccuracies in this equation. Firstly it implies that glucose is the sole respiratory substrate - amino acids, fatty acids and glycerol can be important respiratory fuels.

This equation also does not account for the possibility of anaerobic respiration, where no oxygen is required.

The reaction is also shown to be a single step. Respiration occurs in a series of complex steps, each releasing a small amount of energy. Glycolysis This is an anaerobic process and is the oldest
known respiratory process. This process takes place in the cytoplasm of the cell. Glucose
6C 2x ATP 2x ADP + Pi 2x TP
2x 3C 4x ADP + Pi 4x ATP 2x NAD+ 2x NADH + 2H+ 2x Pyruvate
2x 3C 2x Pyruvate
2x 3C If no O2 present in plants
2x Ethanol + 2CO2 2x 2C 2x 1C The loss of CO2 results in this reaction being irreversible. However, the CO2 can then be used in photosynthesis. If no O2 present in mammals
2x Lactic acid 2x 3C Lactic acid can be turned back into pyruvate in the presence of O2. These processes are useful because they allow glycolysis to continue by unloading the NADH + 2H+ into an intermediate product. As a result, the ATP produced in glycolysis can continue to be produced. CoA CO2 Pyruvate
3C NAD+ NADH + H+ Acetyl CoA
2C Gain: 1x NADH + H+

Total gain: 2x ATP
3x NADH + 3H+ Total gain: 2x ATP
2x NADH + 2H+ Acetyl CoA
2C Citrate
6C NAD+ NADH + H+ CO2 5 carbon compound ADP + Pi ATP 2x FAD 2x FADH2 2x NAD+ 2x NADH + 2H+ Oxaloacetate
4C CO2 Gain: 2x ATP
6x NADH + 6H+
2x FADH2 Total Gain: 6x ATP
10x NADH + 10H+
2x FADH2 Oxidative Phosphorylation This occurs across the inner mitochondrial membrane, and involves the chemiosmosis of hydrogen ions across the membrane from the intermembrane space, via an ATP synthase. The hydrogen carried by the NADH + H+ is split into a constituent proton and electron. The proton is pumped into the space, while the electron enters the E.T.C. NADH + H+ 2e- 2H+ 2e- FADH2 2H+ The FADH2 molecule binds to protein 2 to release its hydrogen. Note that in glycolysis, two molecules of pyruvate are produced, so the gains below have been doubled to account for one Acetyl CoA molecule entering Krebs cycle per molecule of pyruvate. The electrons move down the E.T.C, losing energy as they do so. Some of this energy is lost as heat, while the rest is used to pump hydrogen ions into the intermembrane space. 2e- 2e- 2e- When they reach the end of the E.T.C, the electrons are reunited with a proton, and they combine with oxygen ions to form water. 2e + 2H + O - + 2- H O 2 Due to the hydrogen ions being pumped in, there is now a concentration gradient of hydrogen ions between the inside and outside of the intermembrane space. These ions can only leave the space via chemiosmosis through ATP synthase enzymes. 2H+ ADP + Pi ATP The entire oxidative phosphorylation process produces 34x ATP (3x ATP per NADH + H+, 2x ATP per FADH2). This means that under ideal conditions, the respiration of a single glucose molecule produces 38x ATP. In reality, slightly less than this amount is produced.

The ratio of CO2 produced to the O2 consumed allows us to determine the respiratory substrate of the organism using the respiratory quotient.

RQ ~1.0 - glucose
~0.9 - amino acids
~0.7 - triglycerides
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