ATP and Respiration

ATP and Respiration

1. Anaerobic

   • Animals and Prokaryotes
     • In the cytoplasm, one glucose is phosphorylated into glucose diphosphate using 2 ATP
     • The glucose diphosphate splits into two molecules of triose phosphate
     • The two triose phosphate molecules are dehydrogenated by dehydrogenase, oxidising them into two pyruvate
     • Also, two NAD+ are reduced into NADH and four ATP are formed by substrate-level phosphorylation
     • The two pyruvate accept the hydrogen from the NADH, converting it into NAD+, this froms two lactate
   • Plants and Fungi
     • In the cytoplasm, one glucose is phosphorylated into glucose diphosphate using 2 ATP
     • The glucose diphosphate splits into two molecules of triose phosphate
     • The two triose phosphate molecules are dehydrogenated by dehydrogenase, oxidising them into two pyruvate
     • Also, two NAD+ are reduced into NADH and four ATP are formed by substrate-level phosphorylation
     • The two pyruvate is decarboxylated, releasing carbon dioxide, forming two ethanal
     • The two ethanal accept the hydrogen from the NADH, converting it into NAD+, this froms two ethanol

2. Aerobic Respiration

   • Glycolysis
     • In the cytoplasm, one glucose is phosphorylated into glucose diphosphate using 2 ATP
     • The glucose diphosphate splits into two molecules of triose phosphate
     • The two triose phosphate molecules are dehydrogenated by dehydrogenase, oxidising them into two pyruvate
     • Also, two NAD+ are reduced into NADH and four ATP are formed by substrate-level phosphorylation
   • Link Reaction
     • Pyruvate diffuses from the cytoplasm into the mitochondrial matrix
     • The pyruvate is dehydrogenated with dehydrogenase and the hydrogen is accepted by NAD+ to from NADH
     • The pyruvate is decarboxylated at the same time by decarboxylase to form carbon dioxide
     • When the pyruvate is dehydrogenated and decarboxylated it forms acetate
     • The acetate combine with coenzyme A to form acetyl coenzyme A
   • Kreb's Cycle
     • Acetyl coenzyme A enter the Kreb's cycle by combing with a 4-carbon acid, forming a 6-carbon acid and the coenzyme A is regenerated
     • The 6-carbon acid is dehydrogenated, making NADH and is decarboxylated to make carbon dioxide, forming a 5-carbon acid
     • The 5-carbon acid is dehydrogenated, making NADH and FADH and is decarboxylated to make carbon dioxide and to regenerate the 4-carbon acid
     • The 4-carbon acid can combine with more acetyl coenzyme A and repeat the cycle
     • Each cycle of the Kreb's cycle produces one ATP by substrate-level phosphorylation, three molecules of NADH, one molecule of FADH and two molecules of carbon dioxide

3. Adenosine Triphosphate

   • What is ATP
     • ATP is the universal energy currency, meaning it is used in all cells to drive their reactions
     • ATP is made up of three phosphate molecules, one adenine molecule and one ribose molecule
     • ATP is inert, can pass out of mitochondria into the cytoplasm, releases energy efficiently, releases energy in useable quantities, is easily hydrolysed and is readily reformed by phosphorylation
   • Proton Gradients
     • Photosynthesis
       • Electrons are excited by energy from light, these electrons move through a series of carriers in the thylakoid membranes
       • Their energy pumps protons from the stroma into the spaces between the thylakoid membranes
       • The energy is released in chemiosmosis, in which protons flow back down an electrochemical gradient into the stroma, through ATP synthetase
       • The energy is incorporated into ATP, this ATP drives the light-dependent reactions of photosynthesis and energy is incorporated into the macromolecules made by the cell
     • Respiration
       • Electrons are excited by energy derived from food molecules, their energy is made available as they move through a series of carriers on the inner mitochondrial membrane
       • The energy pumps protons across the membrane, from the matrix into the inter-membrane space, setting up a proton gadient
       • Energy is released in chemiosmosis, as the protons flow back into the matrix through ATP synthetase, and is incorporated into ATP
   • The Electron Transport Chain
     • Respiration
       • Hydrogen atoms derived from the respiratory breakdown of glucose are transferred by dehydrogenase enzymes to coenzymes NAD and FAD and carried to the inner membrane of the mitochondrian
       • The electrons and protons of the hydrogen atoms have different pathways but because they both move through the electron transport chain.
       • For every two protons delivered by NADH, enough energy is released to synthesise three molecules of ATP
       • When FADH delivers two protons, enough energy is released for only two molecules of ATP
     • Photosynthesis
       • Groups of pigments and proteins, called photosystems, transfer excited electrons to electron acceptors and, from there, to a series of proton carriers, all on the thylakoid membranes
       • Protons from the water and the electrons are transferred to the coenzymes NADP and subsequently, to glycerate phosphate, in the pathway that synthesises carbohydrates
       • The energy that powers the proton pump and electron transport chain in the chloroplast comes from light, so chloroplasts synthesise ATP by photophosphorylation