CHAPTER 8How Cells Release Chemical Energy

PhotosynthesisLight energy converted into stored energy

(glucose)CO2 + H2O => C6H12O6 (glucose) + O2Endergonic

Cellular RespirationStored 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 CO2NAD+ 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 Cycle

2 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