Cellular Respiration Harvesting Chemical Energy AP Biology Harvesting
Cellular Respiration Harvesting Chemical Energy AP Biology
Harvesting stored energy § Energy is stored in organic molecules u heterotrophs eat food (organic molecules) § digest organic molecules w serve as raw materials for building & fuels for energy § controlled release of energy w series of step-by-step enzyme-controlled reactions u “burning” fuels § carbohydrates, lipids, proteins, nucleic acids AP Biology 2005 -2006
The Regeneration of ATP (the ATP–ADP Cycle) § ATP is a renewable resource that is • • regenerated by addition of a phosphate group to ADP The energy to phosphorylate ADP comes from catabolic reactions in the cell The chemical potential energy temporarily stored in ATP drives most cellular work AP Biology
Energy from catabolism Is stored into ATP ADP + P AP Biology i Energy from ATP is used for cellular work
Harvesting energy stored in glucose § Glucose is the ideal molecule respiration u catabolism of glucose to produce ATP glucose + oxygen carbon + water + energy dioxide C 6 H 12 O 6 + 6 O 2 6 CO 2 + 6 H 2 O + ATP + heat combustion = making heat energy by burning fuels in one step respiration = making ATP (& less heat) by burning fuels in many small steps ATP fuel AP Biology (carbohydrates) CO 2 + H 2 O + heat CO 2 + H 2 O +2005 -2006 ATP (+ heat)
respiration Harvesting stored energy § Cellular Respiration – process by which cells convert the energy in glucose into usable ATP. glucose + oxygen energy + water + carbon dioxide C 6 H 12 O 6 + 6 O 2 ATP + 6 H 2 O + 6 CO 2 + heat RESPIRATION = making ATP (& some heat) by burning fuels in many small steps enzymes ATP glucose AP Biology O 2 CO 2 + H 2 O + ATP (+ heat)
Background Info… Reduction/Oxidation Reactions § Redox Reactions! Lose Electrons, Oxidize u Gain Electrons, Reduce u AP Biology
Background Info… Reduction/Oxidation Reactions § Redox Reactions! u Follows the movement of ELECTRONS from one chemical to another “X” is losing electrons u “Y” is gaining electrons u AP Biology
How do we harvest energy from fuels? § Digest large molecules into smaller ones u break bonds & move electrons from one molecule to another § as electrons move they carry energy with them § that energy is stored in another bond, released as heat, or harvested to make ATP loses e- gains e- + AP Biology e- oxidized + oxidation reduced + – ereduction 2005 -2006
How do we move electrons in biology? § Moving electrons u in living systems, electrons do not move alone § electrons move as part of H atom loses e- gains e- oxidized + + oxidation H reduced + – H reduction oxidation C 6 H 12 O 6 + AP Biology H 6 O 2 6 CO 2 + 6 H 2 O + ATP reduction 2005 -2006
Electron Carriers! § Introducing…NAD+, a coenzyme electron carrier § NAD+ + 2 e - + H + produces NADH u AP Biology Is NAD+ reduced or oxidized?
Electron Carriers! § Introducing…NAD+, a coenzyme electron carrier § NAD+ + 2 e - + H + produces NADH u AP Biology Gain Electrons Reduce
Electron Carriers! § Also…FAD, a coenzyme electron carrier § FAD + 2 e - + 2 H + produces FADH 2 u Gain Electrons Reduce AP Biology
Moving electrons in respiration § Electron carriers move electrons by shuttling H atoms around u NAD+ NADH (reduced) u FAD+2 FADH 2 (reduced) NAD nicotinamide Vitamin B 3 O– O – P –O O phosphates O– O – P –O O AP Biology H reducing power! NADH O H H O C NH 2 N+ + adenine ribose sugar H reduction O– O – P –O oxidation O O– – P –O O stores energy O as a reduced molecule N+ 2005 -2006
Coupling oxidation & reduction § Redox reactions in respiration u release energy as breakdown molecules § break C-C bonds § strip off electrons from C-H bonds by removing H atoms w C 6 H 12 O 6 CO 2 = fuel has been oxidized § electrons attracted to more electronegative atoms w in biology, the most electronegative atom? O 2 w O 2 H 2 O = oxygen has been reduced § release energy to synthesize ATP oxidation C 6 H 12 O 6 + AP Biology 6 O 2 6 CO 2 + 6 H 2 O + ATP reduction 2005 -2006
Oxidation & reduction § Oxidation § Reduction adding O u removing H u loss of electrons u releases energy u exergonic u removing O u adding H u gain of electrons u stores energy u endergonic u oxidation C 6 H 12 O 6 + 6 O 2 6 CO 2 + 6 H 2 O + ATP reduction AP Biology
Overview of the Process With oxygen present, there are 3 main steps in cellular respiration: 1. 2. 3. AP Biology Glycolysis The Citric Acid Cycle (Krebs Cycle) Oxidative Phosphorylation: ETC and chemiosmosis
NADH and FADH 2 Glucose Glycolysis AP Biology ATP Oxidative Phosphorylation: ETC And Chemiosmosis Pyruva te ATP
Anaerobic Environments When no oxygen is present, the cell will have to do one of two things: Die due to the fact that there is no Oxygen to accept electrons at the end of oxidative, so no more NAD+ are made or u They can undergo Fermentation: u Lactic Acid Alcoholic AP Biology
Overview of cellular respiration § 4 metabolic stages u Anaerobic respiration 1. Glycolysis w respiration without O 2 w in cytosol u Aerobic respiration w respiration using O 2 w in mitochondria 2. Krebs cycle 3. Electron transport chain C H O 6 + AP Biology 6 12 6 O 2 ATP + 6 H 2 O + 6 CO 2 (+ heat)
Cellular Respiration Glucose Glycolysis Oxygen Absent ATP Oxygen Present Anaerobic Respiration Aerobic Respiration (Fermentation) (Krebs Cycle & ETC) AP Biology ATP
Glycolysis § Breaking down glucose u “glyco – lysis” (splitting sugar) glucose pyruvate 2 x 3 C 6 C u most ancient form of energy capture § starting point for all cellular respiration u inefficient § generate only 2 ATP for every 1 glucose u in cytosol § why does that make evolutionary sense? AP Biology
Glycolysis summary invest some ATP harvest a little more ATP & a little NADH AP Biology
How is NADH recycled to NAD+? § Another molecule must accept H from NADH u aerobic respiration § ethanol fermentation § lactic acid fermentation u NADH AP Biology aerobic respiration
Anaerobic ethanol fermentation § Bacteria, yeast pyruvate ethanol + CO 2 3 C NADH 2 C 1 C NAD+ § beer, wine, bread § at ~12% ethanol, kills yeast § Animals, some fungi pyruvate lactic acid 3 C NADH 3 C NAD+ § cheese, yogurt, anaerobic exercise (no O 22005 -2006 ) AP Biology
Pyruvate is a branching point Pyruvate O 2 fermentation Kreb’s cycle mitochondria AP Biology
Pyruvate oxidized to Acetyl Co. A reduction oxidation Yield = 2 C sugar + CO 2 + NADH AP Biology
Count the carbons & electron carriers! pyruvate 3 C FADH 2 AP Biology citrate x 2 4 C 4 C acetyl Co. A 6 C 4 C NADH This happens twice for each glucose molecule 2 C 6 C reduction of electron carriers 4 C ATP 4 C CO 2 NADH 5 C CO 2 NADH
NADH & FADH 2 § Krebs cycle produces: 8 NADH u 2 FADH 2 u 2 ATP u Let’s go to ETC… What’s so important about NADH? AP Biology 2005 -2006
So why the Krebs cycle? § If the yield is only 2 ATP, then why? u value of NADH & FADH 2 § electron carriers § reduced molecules store energy! § to be used in the Electron Transport Chain AP Biology
ATP accounting so far… § Glycolysis 2 ATP § Kreb’s cycle 2 ATP § Life takes a lot of energy to run, need to extract more energy than 4 ATP! Why stop here… AP Biology There’s got to be more to life than this.
Last stop and most important! § Electron Transport Chain u series of molecules built into inner mitochondrial membrane § mostly transport (integral) proteins transport of electrons down ETC linked to ATP synthesis u yields ~34 ATP from 1 glucose! u only in presence of O 2 (aerobic) u AP Biology That sounds more like it!
Don’t forget the Mito! § Double membrane outer membrane u inner membrane (ETC here!) u § highly folded cristae* § fluid-filled space between membranes = intermembrane space u Matrix (Kreb’s here!) § central fluid-filled space * form fits function! AP Biology
Electron Transport Chain AP Biology
Remember the NADH? Glycolysis Kreb’s cycle PGAL 8 NADH 2 FADH 2 2 NADH AP Biology 2005 -2006
Electron Transport Chain or Chemiosmosis § NADH passes electrons to ETC u u AP Biology H cleaved off NADH & FADH 2 electrons stripped from H atoms H+ (H ions) electrons passed from one electron carrier to next in mitochondrial membrane (ETC) transport proteins in membrane pump H+ across inner membrane to intermembrane space
But what “pulls” the electrons down the ETC? AP Biology electrons flow downhill to O 2
Electrons flow downhill § Electrons move in steps from carrier to carrier downhill to O 2 u u u AP Biology each carrier more electronegative controlled oxidation controlled release of energy 2005 -2006
Why the build up H+? § ATP synthase u enzyme in inner membrane of mitochondria ADP + Pi ATP only channel permeable to H+ u H+ flow down concentration gradient = provides energy for ATP synthesis u AP Biology § molecular power generator! § flow like water over water wheel § flowing H+ cause change in shape of ATP synthase enzyme § powers bonding of Pi to ADP § “proton-motive” force 2005 -2006
Cellular respiration AP Biology 2005 -2006
Metabolism § Coordination of digestion & synthesis u by regulating enzyme § Digestion u digestion of carbohydrates, fats & proteins § all catabolized through same pathways § enter at different points u AP Biology cell extracts energy from every source CO 2 2005 -2006
Summary of cellular respiration C 6 H 12 O 6 + 6 O 2 § § § § 6 CO 2 + 6 H 2 O + ~36 ATP Where did the glucose come from? Where did the O 2 come from? Where did the CO 2 come from? Where did the H 2 O come from? Where did the ATP come from? What else is produced that is not listed in this equation? Why do we breathe? AP Biology
Taking it beyond… § What is the final electron acceptor in electron transport chain? O 2 § So what happens if O 2 unavailable? § ETC backs up § ATP production ceases § cells run out of energy § and you die! AP Biology
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