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CHAPTER 8How Cells Release Chemical Energy
PhotosynthesisLight energy converted into stored energy
(glucose)CO2 + H2O => C6H12O6 (glucose) + O2
Endergonic Cellular Respiration
Stored energy (glucose) converted into useable energy (ATP)
C6H12O6 (glucose) + O2 => CO2 + H2O Exergonic
METABOLIC REACTIONS
Aerobic RespirationRequires oxygenHigh energy (ATP) yieldGlycolysis—cytoplasm Kreb’s Cycle—mitochondrial matrixElectron Transport System—cristae
Anaerobic RespirationDoesn’t require oxygenOrganisms without mitochondriaLow energy yield
CELLULAR RESPIRATION
Step 1—Glycolysis Glucose (6C) broken down into two PGAL
(3C)PGAL restructured into pyruvateProduces 2 NADHRequires 2 ATP to startProduces 4 ATPNet gain of 2 ATP
Glucose P-Glucose 2 Pyruvate
AEROBIC RESPIRATION
Step 2a—Acetyl-CoA Pyruvate (3C) combines with CoAReleases CO2
NAD+ NADHForms acetyle-CoA (2C)2 Pyruvate => 2 CO2 + 2 NADH
AEROBIC RESPIRATION
Step 2b—Krebs Cycle 2 Acetyl-CoA enter Transfers carbons to oxaloacetate (C4),
forming citrate (C6) Cycles through steps to rearrange citrate 2 CO2 released Ends forming oxaloacetate Cycle starts again Net gain of 4 CO2, 6 NADH, 2 FADH2, 2 ATP
AEROBIC RESPIRATION
Step 3—Electron Transfer PhosphorylationNADH & FADH2 from previous steps start
chainElectrons flow through “chain” of membrane
proteinsEach protein then takes H+ from above
molecules and pumps them into intermembrane space
This sets up concentration gradientH+ moves down gradient through ATP
synthaseMovement forms ATP from ADP & P (32 net
gain)Ends with electrons passed to O2, combines
with H+ to form H2O
AEROBIC RESPIRATION
AEROBIC RESPIRATION If no oxygen, electrons can’t pass on This backs up to NADPH, so no H+
gradients No ATP forms, starving cells
GlycolysisGlucose + 2ATP 4ATP + 2NADH + 2
Pyruvate Intermediate
2 Pyruvate 2CO2 + 2NADH + 2 Acetyl-CoA
Krebs Cycle2 Acetyl-CoA 6NADH + 2ATP + 2FADH2
Electron Transfer10NADH + 2FADH2 32ATP + 4CO2 + 6H2O
C6H12O6 + 6O2 6H2O + 6CO2 + 36 ATP + heat
AEROBIC RESPIRATION
ANAEROBIC RESPIRATION Fermenters
Protists, bacteriaMarshes, bogs, deep sea, animal gut,
sewage, canned food Some die when exposed to O2
Some indifferent to O2
Some can use O2, but switch to fermentation when none around
ANAEROBIC RESPIRATION Glycolysis happens normally 2 Pyruvate, 2 NADH, 2 Net ATP form Enough energy for many single-celled
species Not enough energy for large organisms
ALCOHOL FERMENTATION Glucose 2 Pyruvate 2 Acetaldehyde
+ 2 CO2
NADH + Acetaldehyde Ethanol
ALCOHOL FERMENTATION Yeasts
BreadBeerWine
LACTATE FERMENTATION Glucose Pyruvate Lactate
LACTATE FERMENTATION Can spoil food Some bacteria create food
Cheese, yogurt, buttermilkCure meatsPickle some fruits & vegetables
LACTATE FERMENTATION Muscle cells
Slow-twitch—light, steady, prolonged activity Marathons, bird migrations Many mitochondria Only aerobic respiration “dark” meat in birds
Fast-twitch—immediate, intense energy Weight lifting, sprinting Few mitochondria Lactate fermentation Produce ATP quickly, but not for long “white” meat in birds
ENERGY STORAGE Glucose absorbed
through intestines When glucose
level rises, glucose converted to glycogenDiverts at glucose-
6-phosphate in glycolysis
ENERGY STORAGE Glycogen is storage polysaccharide Stores in liver & muscles With low blood glucose, insulin released This triggers glycogen to convert back
to glucose If too many carbohydrates/glucose in
blood, acetyl-CoA diverted & made into fatty acid
USING FATS Body stores most fats as triglycerides When glucose levels fall, triglycerides
used Enzymes remove glycerol
USING FATS Glycerol
converted to PGAL
PGAL converted to pyruvate as in glycolysis
USING PROTEINS Happens when eat too many proteins, or
when carbohydrates & fats used Enzymes break down protein molecules Ammonia (NH3) removed Leftover carbon backbone split
Forms acetyl-CoA, pyruvate, or intermediate of Krebs cycle
Specific amino acid determines which is formed