Harvesting energy: photosynthesis & cellular respiration part 1I

Harvesting energy: photosynthesis & cellular respiration part 1I

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

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. for heterotrophic organisms, this is only achieved through the consumption of autotrophic organisms or parts of them! A cell can produce ~36 ATP molecules from one glucose molecule!

Cellular respiration summary equation many steps, many enzymes

III. Making ATP cellular respiration So How do organisms make ATP? A. Cellular respiration (3 steps) 1. Glycolysis 1a. Formation of Aceytl CoA 2. Krebs cycle 3. Mitochondrial e- transport chain B. Anaerobic respiration a viable option for some and a viable short term option for others

1. Step One: 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

1a. 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

2. Citric Acid Cycle (Krebs cycle) Occurs 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

2. 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!

3. 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

3. 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)

What do prokaryotic organisms do? 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

You should be able to answer these questions: CR is the conversion of stored chemical energy to ATP... why is this important? Where in the cell the steps take place Know the summary equation For every glucose molecule, potential for 36 molecules of ATP Both animals AND plants make ATP by cellular respiration

Animals extract energy & other valuable chemicals from molecules other than the simple sugar glucose

III. 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?

III. 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