AQA A2 Unit 4 Respiration

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Stages of Respiration

-Respiration is the oxidation of glucose (or other substrates). During the reaction energy is released from glucose molecules. Much of this energy is used to synthesise ATP

-Aerobic respiration involves four stages.Glycolysis takes place in the cytoplasm. The link reaction and Krebs cycle take place in the Matric of the Mitochondrion. Oxidative phosporylation takes place in the inner membrane (on the cristae) of the Mitochondrion.

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-In Glycolysis, glucose is converted to pyruvate in a series of small steps

-Each glucose molecule is phosphorylated, and then split to form two triose phosphate molecules. Then uses two molecules of ATP for each molecule of glucose 

-NAD takes two electrons from each triose phosphate molecule, becoming reduced NAD.

-As the triose phosphate is converted to pyruvate, enough energy is released to make two molecules of ATP for every triose phosphate - that is, four molecules of ATP for every glucose molecule that we started with.

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Link Reaction + Krebs Cycle

- In the Link Reaction, pyruvate produced in glycolysis moves into a mitochondrion, where it is combined with coenzyme A and decarboxylated to for a 2-carbon compund, Acetylcoenzyme A.

- In the matrix of the mitochondrion, acetylcoenzyme A is combined witha 4-carbon compound to make a 6-carbon compound. This is converted back to a 4-carbon compound in a series of enzyme-controlled steps. In several of these steps, carbon dioxide and/or electrons are removed. The electrons are picked up by NAD of FAD. In one step, ATP is synthesised from ADP and Pi. this cyclic series of reaction is called the Krebs cycle.

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Electron Transport Chain

-The Reduced NAD and FAD pass thier electrons to the first compound in a series of electron carriers situated in the inner membrane of the mitochondrion, called the electron transport chain. The electrons are passed along the chain, and are finally accepted by oxygen forming water.

-The energy released from the electrons as they pass along the electron transport chain is used to pump hydrogen ions from the matrix, across the inner membrane and into the space between the two membranes. As the hydrogen ions move back down thier concentration gradient, they pass through ATPases, and energy from them is used to synthesise ATP.

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Anaerobic Respiration

-Anaerobic respiration takes place when oxygen is in short supply, and the electron transport chain, the krebs cycle and link reaction cannot take place.

-Glycolysis continues as normal.To prevent the build-up of pryuvate , and to regenerate NAD, the pyruvate is converted to either lactate (in animals) or to ethanol and carbon dioxide (in plants and yeast organisms).

-Glycolysis plus either the lactate pathway or the ethanol pathway make up anaerobic respiration.

-Anaerobic respiration generates a very small amount of ATP compared with aerobic respiration,

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Energy Transfer in Photosynthesis and Respiration

-In Photosynthesis, energy from sunlight is used to generate NADP. This donates electrons to carbon dioxide, producting carbohydrates.

-In Respiration, carbohydrates are broken down to release electrons. These are picked up by NAD, which donates the electrons to the electron transport chain. This energy from the electrons is used to produce ATP, the energy currency of every cell

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