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
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)
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
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 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 C H O 6 + AP Biology 6 12 6 O 2 (+ heat) 6 CO 2 + 6 H 2 O + ATP 2005 -2006
Chapter 9. Cellular Respiration STAGE 1: Glycolysis AP Biology
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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