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Cell Respiration part 3 Respiration • Process in which organic molecules act as a fuel – Main fuel molecule: Glucose – Secondary sources of fuel: fatty acids, glycerol, amino acids • Organic molecules broken don in a series of stages • Release chemical potential energy – Used to synthesize ATP • Four stages of glucose break down: 1. 2. 3. 4. Glycolysis Link Reaction Krebs Cycle Oxidative Phosphorylation Review • Phosphorylation – Conversion of an energyrich, but not very reactive, molecule into one that is MUCH more reactive AND whose chemical potential energy can be released and trapped more efficiently CoEnzymes • a nonprotein compound • required for an enzyme to be able to catalyze a reaction – NOT a substrate – Do not become part of the reaction • bind with the protein molecule (apoenzyme) to form the active enzyme (holoenzyme) • bind to the active site of the enzyme and participate in catalysis but are not considered substrates of the reaction • function as intermediate carriers of electrons, specific atoms or functional groups that are transferred in the overall reaction • Examples: NAD, NADP, FAD, CoEnzymeA NAD (Nicotinamide adenine dinucleotide) • Co-enzyme • Carrier molecule • 2 linked nucleotides, each with a ribose – One nucleotide has adenine – One had nictinamide ring (this accepts hydrogen ion and 2 electrons • Becomes “reduced” because it carries hydrogen ions and electrons – “reduced NAD” aka NADH • Removal of hydrogens is called an oxidation reaction • Molecule that picks up the hydrogens is “REDUCED” Other important coenzymes: FAD and NADP • NADP (nicotinamide adenine dinucleotide phosphate) – Slightly different form of NAD in photosynthesis – Has a phosphate group instead of a hydrogen on carbon 1 of the ribose rings – Called NADP (reduced NADP is NADPH) • FAD (flavin adenine dinucleotide) – Similar in function of NAD – Used in Krebs – Made of two nucleotides – one nucleotide containing ribose and adenine – One nucleotide containing unusual structure involving a linear molecule ribitol (instead of ribose) Glycolysis • Means “splitting glucose” • Starting point for respiration in aerobic AND anaerobic conditions – Aerobic with oxygen – Anaerobic no oxygen present • Location: cytoplasm (cytosol) of cell • Multi-step process – Each step is catalyzed by a specific enzyme (IMPORTANT!!!) • ONE six carbon molecule splits into TWO three carbon molecules called PYRUVATE • Energy required to begin (2 ATPs) • Energy released at end (4 ATPs) • Net total: 2 ATPs • In order for Glycolysis to continue, we MUST have steady supply of NAD Glucose (Hexose) (6C) ATP Fructose phosphate (6C) ATP 2 ATP 2H 2 NAD 2 Reduced NAD 2 ATP Glycolysis • First stage Phosphorylation with ATP (substrate level phosphorylation) – 1st ATP to glucose glucose phosphate fructose phosphate – 2nd ATP to fructose phosphate Fructose bisphosphate – Fructose bisphosphate immediately breaks up into TWO molecules of triose phosphate – Inorganic phosphate added to each triose phosphate creates triose bisphosphates • Second Stage Dehydrogenation – A phosphate is removed from each triose bisphosphate--. Back to 2 triose phosphates – Hydrogen is removed from each triose phosphate by NAD 2 reduced NAD molecules – Reduced NAD travels to mitochondria to be used in oxidative phosphorylation • Third Stage Dephosphorylation – Phosphate from triose intermediates removed to yield TWO more ATP molecules • Product: 2 molecules of pyruvate (contains A LOT of chemical potential energy) – When oxygen available, some of energy will be released via Krebs cycle and oxidative phosphorylation Pyruvate + CoA + NAD acetyl CoA + CO2 + reduced NAD • Pyruvate enters mitochondria via ACTIVE transport – Through outer AND inner membranes of mitochondria into MATRIX • In the matrix, pyruvate is: – DECARBOXYLATED – Carbon dioxide molecule removed – Diffuses out of mitochondria – DEHYDROGENATED – Hydrogen is removed (via NAD) – Combined with Coenzyme A – Makes a molecule called ACETYL Coenzyme A CoEnzyme A • Complex molecule • Composed of: – nucleoside – Adenine + Ribose – Vitamin – Pantothenic acid • Acts as a carrier of acetyl groups to the Krebs cycle • Proteins – Amino acids • Fatty Acids – Broken down in mitochondria in a cycle of reactions in which each turn of cycle shortens the fatty acid chain by a two-carbon acetyl group – Each acetyl group can react with CoEnzyme A Acetyl CoEnzyme A – Acetyl CoEnzyme A can now enter Krebs Cycle – Oxygen MUST be present • In order to BURN fat (break of those acetyl groups in a fatty acid) you must conduct AEROBIC types of exercise Krebs Cycle • Citric Acid Cycle • Tricarboxylic Acid Cycle (TCA) • 1937, Hans Krebs • Closed pathway of enzyme controlled reactions • Location : Matrix of Mitochondria • Most important aspect: the release of hydrogens (that go onto oxidative phosphorylation to make ATP) • In: – Acetyl CoEnzyme A Enters • Out: – – – – Carbon Dioxide released Reduced NAD released Reduced FAD released ATP is made Steps of Krebs Cycle • Acetyl CoEnzyme A combines with fourcarbon compound (OXALOACETATE) six- carbon compound (CITRATE) • Citrate is DECARBOXYLATED (carbon dioxide removed) then DEHYDROGENATED (hydrogen removed by NAD and FAD) • OXALOACETATE regenerated at the end of the cycle so it can happen all over again • Products: – ONE turn of Krebs yields: – – – – TWO carbon dioxide molecules ONE reduced FAD THREE reduced NAD ONE molecule of ATP (via intermediate)