revision respiration
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respiration
A REVISION OF THE PRE-SUMMER WORK
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What respiration actually is…
"Respiration is the chemical process of releasing energy from organic compounds."
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It is important that you understand the correct terms for some of the processes:• Gas exchange - The movement of oxygen into an
organism and carbon dioxide out of an organism.• Breathing - The ventilation movements that are
needed in some larger animals so that efficient gas exchange can take place. It involves ribs, intercostal muscles, the diaphragm and lungs.
• Respiration - The process by which complex organic molecules are broken down to release energy.
• Aerobic respiration - Requires oxygen to fully oxidise the organic molecule. This releases lots of energy.
• Anaerobic respiration -The breakdown of the molecule without oxygen. This releases much less energy.
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ATP• ATP (adenosine triphosphate) is the universal
currency of energy. It is a small molecule with 3 phosphate groups (P) attached to an adenosine molecule i.e. Adenosine-P-P-P
• During respiration, high energy C-C, C-H and C-OH bonds are broken. Lower energy bonds are formed and the difference is released and used to attach a P to Adenosine-P-P (ADP adenosine diphosphate), making ATP.
When energy is required at a later time by a cell, it can use the ATP and break a P off the end. This releases the energy needed (30.6kJ for every ATP, ADP + P). The more ATPs used, the more energy is released.
• For aerobic respiration to occur, the cell needs to possess mitochondria.
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An outline of the stages of respiration• Glycolysis (splitting of sugar): What =
formation of pyruvic acid from glucose. Where = cytoplasm of a cell.
• Krebs cycle: What = removal of hydrogen from pyruvic acid. Where = matrix of the mitochondria.
• Electron transport chain / oxidative phosphorylation: What = using hydrogen to produce ATP. Where = inner mitochondrial membrane.
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Electron / hydrogen carriers
• Many of the reactions in the stages of respiration involve oxidation by the removal of electrons or hydrogen atoms (H). These are transferred to electron/hydrogen carriers. Ultimately they are passed to oxygen to form water right at the very last stage of respiration.
• Two important electron/hydrogen carriers are NAD (nicotinamide adenine dinucleotide), and FAD (flavin adenine dinucleotide).
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Oxidation / reduction
• Oxidation is the addition of oxygen, the removal of hydrogen or the loss of electrons.
• Reduction is the addition of hydrogen, the removal of oxygen or the gain of electrons.
• A quick way to remember this is "OILRIG":
• Oxidation Is Loss, Reduction Is Gain.
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Glycolysis
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Glycolysis
1.Glucose is phosphorylated twice to make a 6C sugar phosphate. 2 ATPs are used to supply the P groups. This makes the glucose more reactive and so…
2.The 6C sugar phosphate breaks down to form 2, 3-carbon sugar phosphates, called triose phosphates (TP).
3.Hydrogen is removed from each of the 2 TP molecules. The hydrogens are passed to 2 NADs (the NADs are reduced). 2 ATPs are made directly from the conversion of each TP to pyruvic acid (written shorthand as PA or called pyruvate) as the phosphate groups are removed.
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Glycolysis
Into glycolysis:
• 1 glucose (6C)• 2 NAD• 2ATP
Out of glycolysis
• 2 pyruvic acid (3C)• 2 reduced NAD
(2NADH + H+)• 4 ATP
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Glycolysis
• Net Gain = 2 ATP and 2 NADH + H+
• This stage occurs in the cytoplasm. The next stage occurs in the mitochondria. From here, the reaction will only proceed if oxygen is available.
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The link reaction
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The link reaction
1.The PA molecules enter the mitochondrion.
2.CO2 and hydrogen are removed from each PA to create 2 2-C molecules. The hydrogen is transferred to NAD
3.The 2-C molecule is then combined with coenzyme A (CoA) to form the 2C compound, acetylCoA. (CoA is a vitamin derivative which acts as a transporter of the 'acetate' psrt left from the PA molecule)
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The link reaction
Into link:
2 PA and 2 CoA
2NAD
Out of the link:
2 Acetyl CoA
2CO2
2 reduced NAD (2NADH + H+)
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Krebs Cycle
• This is also known as the citric acid cycle or the tricarboxylic acid cycle.
• For each glucose molecule, there were 2 pyruvic acid molecules formed, (and therefore 2 acetylCoA molecules formed) so the whole cycle takes place twice for every glucose molecule respired.
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Krebs Cycle
1.Each acetylCoA (2C) combines with an oxaloacetic acid (4C) to make a 6C compound (citric acid).
2.In a series of steps, for each 6C compound, 2 CO2 molecules are released, 3 NAD molecules are reduced, 2 FAD molecules are reduced,1 ATP molecule is made directly.
3.The 4C compound is regenerated (by the removal of the 2 Cs in 2 CO2 molecules) so that the cycle can begin again with more molecules of acetylCoA.
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Krebs Cycle
Into Krebs:
2 acetylCoA
6 NAD
2 FAD
2 ADP + P
Out of Krebs:
2 oxaloacetate
4 CO2
6 reduced NAD (6 NADH + H+)
2 reduced FAD (2 FADH + H+)2 ATP