Harvesting energy: photosynthesis & cellular respiration

Harvesting energy: photosynthesis & cellular respiration

Learning Objectives Know the relationship between photosynthesis & cellular respiration Know the formulae of the chemical reactions for photosynthesis & cellular respiration Be able to recognize and explain the various steps within cellular respiration Understand the importance of cellular respiration to life

Agenda I. Overview (Big Pictures) of Photosynthesis & Cellular Respiration II. Making ATP - Cellular Respiration Aerobic Anaerobic

I. Photosynthesis, the big picture The transformation of carbon dioxide and water using light energy to create stored chemical energy (glucose) photo part: light energy is captured & turned into ATP synthesis part: ATP fuels the production of sugar (glucose)

Photosynthesis summary equation many steps, many enzymes

I. Cellular respiration, the big picture The conversion of stored chemical energy to ATP (or just the making of ATP) Why do cells do this? Both plants & animals do cellular respiration. Glucose is the main source of stored chemical energy for the cell. A cell can produce 36 ATP molecules from one glucose molecule!

Cellular respiration summary equation many steps, many enzymes

II. Making ATP cellular respiration So How do organisms make ATP? A. Cellular respiration (3 steps) 1. Glycolysis 2. Krebs cycle 3. Oxidative Phosphorylation B. Anaerobic respiration a viable option for some and a viable short term option for others

II. Cellular Respiration Glycolysis The initial splitting of glucose into two pyruvate molecules occurs in all cells (prokaryotic or eukaryotic) does not require oxygen to proceed results in a net formation of 2 ATP 2 pyruvate 2 NADH + 2H + **Main purpose of glycolysis: to form pyruvate and coenzymes to be used in the next step! for some small single celled organisms, with low energy demands, glycolysis may produce enough ATP, for others they need more!

II. Eukaryotic Aerobic Cellular Respiration Oxidation of Pyruvate to Acetyl CoA The link between glycolysis and the citric acid cycle Cytosol Mitochondrial Matrix c c c Pyruvate NAD + CO 2 c NADH + H + Coenzyme A CoA CoA c c Acetyl CoA Transport protein inner mitochondrial membrane outer mitochondrial membrane

II. Eukaryotic Aerobic Cellular Respiration Citric Acid Cycle (Krebs cycle) In the mitochondrial matrix Molecules produced during glycolysis (pyruvate) are further broken down Produces more ATP & high energy e- carriers 2 ATP 6 NADH electron carrier 2 FADH 2 electron carrier ** Main purpose of the Krebs cycle is to supply e- and e- carriers for step 3

II. Eukaryotic Aerobic Cellular Respiration Citric Acid Cycle each acetyl CoA enters into the citric acid cycle when it combines with the end product of the prior cycle. series of reduction and oxidation reactions leads to the formation of: 3 NADH + H + 1 FADH 2 2 CO 2 oxaloacetate (end product) GDP is phosphorylated to GTP as energy is released allowing for the production of 1 ATP Why do we care about the production of NADH + H + and FADH 2? These products drive the next step!

II. Eukaryotic Aerobic Cellular Respiration Oxidative Phosphorylation Takes place across inner membrane of mitochondria About 90% of energy harvested in this step Involves e - transport chain & chemiosmosis ***O 2 necessary for ATP production; e - would not travel w/o O 2 to allow the gradient to continue 36 ATP molecules are made for every glucose molecule

II. Eukaryotic Aerobic Cellular Respiration Oxidative Phosphorylation Two major components to this: 1. The electron transport chain (ETC) electrons (from?) provide energy to transport protons into the intermembrane space this creates a proton gradient oxygen accepts the electrons and with protons creates water 2. Chemiosmosis an inner mitochondrial membrane protein called ATP synthase synthesizes ATP using the proton gradient (proton motive force) Why go through this process, when we can get ATP directly from glycolysis? Efficiency! each NADH has enough power to generate 3 ATP molecules (max 10 NADH in = 30 ATP) each FADH 2 has enough power to generate 2 ATP molecules (min 2 FADH 2 in = 4 ATP)

III. Prokaryotic Aerobic Cellular Respiration Prokaryotes contain no mitochondria so glycolysis and citric acid cycle take place in the cytosol oxidative phosphorylation takes place across the cell s plasma membrane H + H + H + H+ H + H + H + Bacterium Periplasmic Space e - H + H + H e - + + H + e - e - NADH + H + NAD + Electron Transport glycolysis Cytosol + O H 2 0 Chemiosmosis Citric acid cycle ATP synthase cell membrane cell wall and outer membrane

II. Cellular respiration - Summary CR is the conversion of stored chemical energy to ATP... why is this important? takes place in the mitochondria of eukaryotic cells and the cytoplasm of prokaryotic cells C 6 H 12 O 6 + 6O 2 6CO 2 + 6H 2 O + ATP + Heat For every glucose molecule, potential for 36 molecules of ATP Both animals AND plants make ATP by cellular respiration

Other Options! Animals extract energy & other valuable chemicals from molecules other than the simple sugar glucose Why do you think carbohydrates are used as a first choice for cellular metabolism?

II. Making ATP without oxygen Fermentation Same metabolic pathways as glycolysis Breaks glucose into 2 molecules of pyruvate Generates 2 ATP Many bacteria & yeasts do this bacteria lack mitochondria... their energy needs are lower than multicellular organisms Why can t cellular respiration take place without oxygen?

II. Making ATP without oxygen Two types of Fermentation Lactic acid fermentation convert pyruvate to lactate bacteria do this (and you, too!) how cheese & yogurt are made Alcohol fermentation convert pyruvate to CO 2 and ethanol yeast do this brewing, winemaking, baking

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