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How Cells Release Chemical Energy
 Photosynthesis
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Light energy converted into stored energy
(glucose)
CO2 + H2O => C6H12O6 (glucose) + O2
Endergonic
 Cellular
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Respiration
Stored energy (glucose) converted into useable
energy (ATP)
C6H12O6 (glucose) + O2 => CO2 + H2O
Exergonic
 Aerobic
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Respiration
Requires oxygen
High energy (ATP) yield
Glycolysis—cytoplasm
Kreb’s Cycle—mitochondrial matrix
Electron Transport System—cristae
 Anaerobic
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Respiration
Doesn’t require oxygen
Organisms without mitochondria
Low energy yield
 Step
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1—Glycolysis
Glucose (6C) broken down into two PGAL (3C)
PGAL restructured into pyruvate
Produces 2 NADH
Requires 2 ATP to start
Produces 4 ATP
Net gain of 2 ATP
 Glucose
 P-Glucose  2 Pyruvate
 Step
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2a—Acetyl-CoA
Pyruvate (3C) combines with CoA
Releases CO2
NAD+  NADH
Forms acetyle-CoA (2C)
2 Pyruvate => 2 CO2 + 2 NADH
 Step
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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
 Step
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3—Electron Transfer Phosphorylation
NADH & FADH2 from previous steps start chain
Electrons flow through “chain” of membrane
proteins
Each protein then takes H+ from above molecules
and pumps them into intermembrane space
This sets up concentration gradient
H+ moves down gradient through ATP synthase
Movement forms ATP from ADP & P (32 net gain)
Ends with electrons passed to O2, combines with
H+ to form H2O
 If
no oxygen, electrons can’t pass on
 This backs up to NADPH, so no H+ gradients
 No ATP forms, starving cells
 Glycolysis
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Glucose + 2ATP  4ATP + 2NADH + 2 Pyruvate
 Intermediate
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2 Pyruvate  2CO2 + 2NADH + 2 Acetyl-CoA
 Krebs
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Cycle
2 Acetyl-CoA  6NADH + 2ATP + 2FADH2
 Electron
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Transfer
10NADH + 2FADH2  32ATP + 4CO2 + 6H2O
 C6H12O6
+ 6O2  6H2O + 6CO2 + 36 ATP + heat
 Fermenters
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Protists, bacteria
Marshes, 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
 Glycolysis
happens normally
 2 Pyruvate, 2 NADH, 2 Net ATP form
 Enough energy for many single-celled species
 Not enough energy for large organisms
 Glucose
 2 Pyruvate  2 Acetaldehyde + 2
CO2
 NADH + Acetaldehyde  Ethanol
 Yeasts
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Bread
Beer
Wine
 Glucose
 Pyruvate  Lactate
 Can
spoil food
 Some bacteria create food
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Cheese, yogurt, buttermilk
Cure meats
Pickle some fruits & vegetables
 Muscle
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Slow-twitch—light, steady, prolonged activity
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cells
Marathons, bird migrations
Many mitochondria
Only aerobic respiration
“dark” meat in birds
Fast-twitch—immediate, intense energy
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Weight lifting, sprinting
Few mitochondria
Lactate fermentation
Produce ATP quickly, but not for long
“white” meat in birds
 Glucose
absorbed
through intestines
 When glucose level
rises, glucose
converted to
glycogen
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Diverts at glucose-6phosphate in
glycolysis
 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
 Body
stores most fats as triglycerides
 When glucose levels fall, triglycerides used
 Enzymes remove glycerol
 Glycerol
converted
to PGAL
 PGAL converted to
pyruvate as in
glycolysis
 Happens
when eat too many proteins, or
when carbohydrates & fats used
 Enzymes break down protein molecules
 Ammonia (NH3) removed
 Leftover carbon backbone split
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Forms acetyl-CoA, pyruvate, or intermediate of
Krebs cycle
Specific amino acid determines which is formed