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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 CO2 & H2O
Respiration• means breathing
• cellular respiration
– exchange of gases
• O2 from environment is used & CO2 is released & removed by blood
Cellular Respiration• provides ATP for cellular work
• called oxidation
• oxidizes food molecules, like glucose, to CO2 & water
• 6C6H12O2 + 6O2 6CO2 + 6H2O + ATP
• energy is trapped in ATP
Cellular Respiration-Oxidation• electrons are transferred from sugar to
O2 making H2O• do not see electron transfer in equation• see changes in H ions• glucose molecule loses hydrogen
atoms as it is converted to CO2 • O2 gains hydrogen atoms to form water• O2 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 O2
• it is as if they are falling• energy is released in the process• process is possible only because of O2
• if you stop breathingno ATP would be madeall processes stopdeath
6C6H12O2 + 6O2 6CO2 + 6H2O + ATP
Complete Oxidation of Glucose• C6H12O6 + 6O2 6CO2 + 6H2O
• 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 lostoxidized-loses
energy• Reduction
– H+ atoms are added to compounds
• gain electronreduced-gains energy
• food fuels are oxidized-lose energy transferred to other moleculesATP
• 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 O2
– aerobic
• Electron Transport Chain– occurs in mitochondria
– require O2
– aerobic
Glycolysis• first step in complete
oxidation of glucose• occurs in cytosol• begins when enzyme
phosphorylates glucose– adds PO4 group to
glucose Glu6PO4• traps glucose• reaction uses 2 ATPs• Energy Investment
Phase
Glycolysis• Sugar Splitting
Stage
• 6 carbon compound2 pyruvates (3 carbon compounds)
ATP
Glycolysis
Pyruvate• fate depends on oxygen
availability• not enough oxygen
– NAD+ is regenerated by converting pyruvatelactic acid
• anaerobic fermentation• O2 available• pyruvic acid enters
aerobic pathways of Krebs cycle
• aerobic respiration
Anaerobic Fermentation• not enough oxygen• NAD+ regenerated by
converting pyruvatelactic 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 CO2 + 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 moleculestransferred to coenzymes
• cycle begins & ends with same substrate: oxaloacetate (OAA)
• acetyl CoA condenses with oxaloacetate- 4 carbon compoundcitrate-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 CO2
– reducing equivalents-3 NADH & 1 FADH2
• further oxidized in electron transport chain
– 1 GTP-ATP equivalentSince 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 O2 atoms
• reactions takes place on inner mitochondrial membrane
• only permeable to water, oxygen & CO2
Oxidative Phosphorylation/Electron Transport Chain System
• responsible for 90% of ATP used by cells
• basis-2H + O22 H20• 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 proteinATP synthase attaches PO4 to ADP ATP
ATP synthase
Oxidative Phosphorylation• for each pair
of electrons removed by NAD from substrate 3 ATPs are made
• FAD2 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 FADH2 X 2=4 ATP
• 2 moles pyruvate2 NADH + H+-glycolysis 2 X 2 = 4 ATP
• Total 36 ATP
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