Respiration and Energy


Energy Production

The majority of enegry in the body is released from ATP (Adenosine Triphosphate)

This molecule is made up of an Adenine base and a Ribose sugar (adenosine) plus three phosphate groups.


The process above releases roughyl 30.6kJ of energy

ADP+Pi---->Condensation---->ATP (resynthesis of ATP)

Energy is needed in the body for:

Active Transport, Secretion, Movement, DNA replication, Endocytosis

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Glycolysis occurs in the cytoplasm/cytosol of the mitchondria.


1. 6C Glucose phosphorylated. 2x ATP molecules used

2. Produces Hexose Bisphosphate which splits in two to create 2x Triose Phosphate.

3. Each triose phosphate is oxidised to produce 2x NADH+H+. They also go through dephosphorylation whihc produces 4x ATP.

4. End product is pyruvate. Net gain of ATP is 2 molecules.

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Links Reaction

The Links Reaction occurs in the matrix of the mitochondria.


1. Starting substance is Pyruvate 3C

2. Decarboxylation through the action of pyruvate decarboxylase- CO2 produced

3. Dehydrogenation through the action of pyruvate dehydrongenase- NADH+H+ produced

4. Coenzyme A added

5. Final product is Acetyl CoA

6. Occurs twice for each glucose molecule (2x CO2 molecules and 2x NADH+H+ produced)

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Krebs Cycle

The Krebs Cycle occurs in the matrix of the mitochondria


1. 2C joins with 4C, CoA removed---> 6C acid (citrate)

2. Decarboxylation and dehydrogenation occurs ( CO2 and NADH+H+ produced)

3. Produce a 5C acid --------> 4C acid (oxloacetate)

4. 5C--->4C produces: 2x NADH+H+, 1xFADH2, 1xATP, 1xCO2

5. Two turns for each glucose molecule: 6xNADH+H+, 2xFADH2, 4xCO2, 2xATP

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Oxidative Phosphorylation

Oxidaitve Phosphorylation occurs in the mitochondrial membrane.


1. The reduced NAD and FAD 'donate' hydrogen atoms to the electron carriers. These atoms are split into protons and electrons.

2. The electrons are passed along a chain of carriers. Energy from this is used to pump protons into the intermembrane space.

3. This creates a proton gradient.

4. Protons then diffuse through the channel protein. The flow of these hydrogen ions/protons is chemiosmosis.

5. ATPsynthase produces ATP.

6. Protons combine with the electrons and oxygen atoms to form water.

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Respiratory Quotient

Respiratory qouoient (RQ)= volume of CO2 produced/ volume of O2 consumed (in the same period of time)

RQ value for; Carbohydrates- 1.0

                       Proteins- 0.9 (proteins enter Krebs after going through beta-oxidation)

                       Lipids- 0.7 (also enter krebs after beta-oxidation)

If the RQ value isn't nay of these than a variety of substrates have been used e.g an RQ of 0.8 could be Proteins and Lipids.

The RQ value RISES when respiration is anaerobic.                                           

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Anaerobic Respiration

Anrobic respiration starts off in the same way as aerobic respiration-

Glycolysis occurs to produce 2 ATP molecules per glucose molecule

However, there is not enoguh oxygen present after this so the process is halted.

The pyruvate that was formed in glycolysis is converted in lactate during lactate fermentation.

ATP-PC system:

Creatine Phosphate/ Phosphocreatine is stored in the muscles. It is broken down into Creatine and Phosphate to release energy. This is a very short term supply as there are not large stores of PC in the muscles.

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