Cellular Respiration

Energy Flow photosynthesis –carried out by plants uses energy from sunlight converts into glucose & oxygen used in cellular respiration oxygen is consumed glucose is broken down  CO 2 & H 2 O

Respiration means breathing cellular respiration –exchange of gases O 2 from environment is used & CO 2 is released & removed by blood

Cellular Respiration provides ATP for cellular work called oxidation oxidizes food molecules, like glucose, to CO 2 & water 6C 6 H 12 O 2 + 6O 2    6CO 2 + 6H 2 O + ATP energy is trapped in ATP

Cellular Respiration-Oxidation electrons are transferred from sugar to O 2 making H 2 O do not see electron transfer in equation see changes in H ions glucose molecule loses hydrogen atoms as it is converted to CO 2 O 2 gains hydrogen atoms to form water O 2 is an electron grabber –pulls harder than other atoms to get electrons these hydrogen movements represent electron transfers each hydrogen atom consists of one electron and one proton electrons move along with hydrogens from glucose to O 2 it is as if they are falling energy is released in the process process is possible only because of O 2 if you stop breathing  no ATP would be made  all processes stop  death 6C 6 H 12 O 2 + 6O 2    6CO 2 + 6H 2 O + ATP

Complete Oxidation of Glucose C 6 H 12 O 6 + 6O 2  6CO 2 + 6H 2 O for one thing to be oxidized-another must be reduced oxidation & reduction reactions occur together redox reactions

Oxidation/Reduction Reactions Oxidation –H + atoms are removed from compounds Oxidized things lose electrons electron lost  oxidized-loses energy Reduction –H + atoms are added to compounds gain electron  reduced-gains energy food fuels are oxidized-lose energy  transferred to other molecules  ATP coenzymes act as hydrogen or electron acceptors –reduced each time substrate is oxidized

CoEnzymes NAD + -niacin-nicotinamide adenine dinucleotide FAD-flavin adenine dinucleotide-riboflavin

Glucose Oxidation Steps Glycolysis –occurs in cytosol –does not require oxygen –also called anaerobic Kreb’s Cycle –occurs in mitochondria –require O 2 –aerobic Electron Transport Chain –occurs in mitochondria –require O 2 –aerobic

Glycolysis first step in complete oxidation of glucose occurs in cytosol begins when enzyme phosphorylates glucose –adds PO 4 group to glucose  Glu6PO4 traps glucose reaction uses 2 ATPs Energy Investment Phase

Glycolysis Sugar Splitting Stage 6 carbon compound  2 pyruvates (3 carbon compounds) ATP

Glycolysis

Pyruvate fate depends on oxygen availability not enough oxygen –NAD + is regenerated by converting pyruvate  lactic acid anaerobic fermentation O 2 available pyruvic acid enters aerobic pathways of Krebs cycle aerobic respiration

Anaerobic Fermentation not enough oxygen NAD + regenerated by converting pyruvate  lactic acid limited by buildup of lactic acid –produces acid/base problems –degrades muscle performances used for short bursts of high level activity lasting several minutes cannot supply ATP for long, endurance activities

Alcohol Fermentation yeast without oxygen provides ATP by product- ethanol regenerates NAD +

Aerobic Respiration pyruvic acid enters mitochondria once inside  converted  acetyl CoA during conversion pyruvate is decarboxylated (carbons removed) released as CO pyruvic acid + NAD + + coenzyme A  CO 2 + NADH + Acetyl CoA

Krebs Cycle acetyl CoA enters Krebs Cycle –tricarboxylic acid cycle or Citric Acid Cycle during cycle hydrogen atoms are removed from organic molecules  transferred to coenzymes cycle begins & ends with same substrate: oxaloacetate (OAA) acetyl CoA condenses with oxaloacetate- 4 carbon compound  citrate-6 carbon compound cycle continues around through 8 successive step during steps atoms of citric acid are rearranged producing different intermediates called keto acids eventually turns into OAA

Krebs Cycle Yields –2 CO 2 –reducing equivalents-3 NADH & 1 FADH 2 further oxidized in electron transport chain –1 GTP-ATP equivalent Since two pyruvates are obtained from oxidation of glucose  amounts need to be doubled for complete oxidation results

Electron Transport Chain transfers pairs of electrons from entering substrate to final electron acceptor- oxygen electrons are led through series of oxidation- reduction reactions before combining with O 2 atoms reactions takes place on inner mitochondrial membrane only permeable to water, oxygen & CO 2

Oxidative Phosphorylation/Electron Transport Chain System responsible for 90% of ATP used by cells basis-2H + O 2  2 H 2 0 releases great deal of energy all at once cells cannot handle so much energy reactions occur in series of steps Oxidation reactions –remove H + atoms & lose energy (H + ) Oxidized things lose electrons compounds that gain electrons  reduced-gain energy enzymes cannot accept H atoms Coenzymes needed to accept hydrogens when coenzyme accepts hydrogen atoms  coenzyme reduced & gains energy

Chemiosmosis ETC creates conditions needed for ATP production by creating concentration gradient across inner mitochondrial membrane as energy is released-as electrons are transferred  drives H ion pumps that move H across membrane into space between 2 membranes pumps create large concentration gradients for H H ions cannot diffuse into matrix because not lipid soluble channels allow H ions to enter matrix Chemiosmosis –energy released during oxidation of fuels=chemi –pumping H ions across membranes of mitochondria into inter membrane space =osmo –creates steep diffusion gradient for Hs across membrane when hydrogens flow across membrane, through membrane channel protein  ATP synthase attaches PO 4 to ADP  ATP ATP synthase

Oxidative Phosphorylation for each pair of electrons removed by NAD from substrate 3 ATPs are made FAD  2 ATPs are made

Energy Yield aerobic metabolism generates more ATP per mole of glucose oxidized than anaerobic metabolism Glycolysis –net 2 ATPs Krebs Cycle –2 ATP –8 NADH + H + X 3=24 ATP –2 FADH 2 X 2=4 ATP 2 moles pyruvate  2 NADH + H + - glycolysis  2 X 2 = 4 ATP Total 36 ATP