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ATP: Adenosine Triphosphate
ATP ADP + Pi (Hydrolysis, energy release)
ADP + Pi ATP (Condensation)
Properties of ATP:
-Small and soluble (easily transported in cells)
-Easily hydrolysed (instantaneous release)
-Remade easily (condensation, regeneration)
-Makes molecules reactive (phosphorylation)
-Cannot pass out of the cell
ATP used in active process e.g. active transport
Made up of adenine, ribose and 3 x phosphates
ATP is made by:
-Respiration in animals and plants
-Photosynthesis in plants
Glycolysis overview:
Glycolysis splits glucose into smaller molecules of pyruvate and occurs in the cytoplasm of cells. It is split into two stages:
Phosphorylation:
-Glucose is phosphorylated using a phosphate taken from an ATP molecule.
-Another phosphate is added making hexose bisphosphate.
-Hexose phosphate is then split to form two molecules of triose phosphate.
Oxidation:
-Triose phosphate(s) oxidised to pyruvate(s), regenerating 4 x ATP per glucose, as well as 2 molecules of reduced NAD.
*Net gain of 2 x ATP, 2 x NADH and 2 x pyruvate
Link reaction explained:
-Pyruvate decarboxylated then oxidised by NAD.
-This forms acetate, which then combines with coenzyme A to form acetyl-CoA.
-No ATP produced
Anaerobic respiration:
Decarboxylation: Where a carboxyl (CO2) group is removed from a compound.
Dehydrogenation: Removal of hydrogen
Oxidation: Where a species loses electrons
Reduction: Where a species gains electrons
Substrate-level phosphorylation: Where a phosphate group is transferred from an intermediate compound to a species.
Oxidative phosphorylation:
The purpose of oxidative phosphorylation is to use the energy carried by the electrons in NADH and FADH2 to generate ATP through a condensation reaction. It occurs across the inner mitochondrial membrane (double-membrane bound).
-Various protein complexes span the IMM.
-Reduced NAD and FAD are oxidised at one of these protein complexes. This oxidation releases electrons and hydrogen ions (H+/protons).
-The electrons move down an ETC (electron transport chain) across the protein complexes.
-The movement of electrons is coupled to the pumping of H+ ions into the inter-membrane space, building an electrochemical gradient (H+ gradient)
-H+ ions move back down their electrochemical gradient through ATP synthase, which combines Pi to ADP through rotary motion, forming ATP.
-Oxygen acts as the terminal electron acceptor in the ETC. It combines with H+ ions and electrons to form water (H2O).
-This process is known as chemiosmosis.
C6H12O6 + 6O2 6CO2 + 6H2O (+ATP also made)
Mitochondria
Structure and function:
Mitochondria are double-membrane bound organelles responsible for carrying out respiration. They share similarities to bacteria in shape and structure, and also have their own DNA.
Matrix: The aqueous medium inside a mitochondrion. This is where the electrochemical gradient is established to drive ATP synthesis.
Cristae: Folds in the inner membrane of the mitochondrion. This helps the inner membrane to have a large surface area, for an increased amount of reactions to occur on (chemiosmosis)
Anaerobic respiration:
-Pyruvate in glycolysis converted to lactate (animals) or ethanol (plants) using reduced NAD.
-Regeneration of NAD allows glycolysis to continue and therefore making ATP
-Lactate turns to lactic acid which causes muscle fatigue. It is overcome by repaying oxygen debt.
Krebs cycle explained:
The purpose of the Krebs cycle is to use the acetyl CoA (formed from the link reaction), a 4C compound and a series of redox reactions to release ATP and reduced coenzymes (NADH, FADH2 for oxidative phosphorylation). This occurs in the matrix.
Combination + dissociation:
-Acetyl CoA combines with oxaloacetate (4C) to form a 6C citrate compound. CoA leaves here and is returned to the link reaction.
Decarboxylation + Dehydrogenation:
-A primary decarboxylation event shortens the 6C to a 5C compound. Here another NAD is reduced to NADH.
-This reduction is driven by dehydrogenation.
-A secondary decarboxylation event shortens the 5C to the 4C oxaloacetate initially used (regeneration).
-Here another 2 NAD are reduced to NADH, and a FAD is reduced to FADH2. ATP is also made via condensation of ADP + Pi
-The reduction of NAD and FAD involves another dehydrogenation step.
-ATP production is driven by a phosphate transfer from one of the intermediates. This is known as substrate level phosphorylation.
ATP Synthase
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