ACQUIRING ENERGYChapter 6

Energy for Life• All energy comes from the sun

– Producers convert light into chemical energy (glucose bonds)

– Consumers eat/break bonds to release energy

• Energy coupling reactions recycle components– Cellular respiration (break):

• 6O2 + C6H12O6 6CO2 + 6H2O + ATP– Photosynthesis (make):

• ATP + 6CO2 + 6H2O C6H12O6 + 6O2

• Which reaction term applies to each?

Redox Reactions• Coupled reactions that move electrons between

molecules– Review: electrons form bonds and energy is released

when they break (endergonic or exergonic?)

• LEO goes GER– Lose an electron = oxidation

• Glucose oxidized to CO2

– Gain an electron = reduction• O2 reduced to H20

• NAD+ reduced to NADH

– What do all these reactions have in common?

Electron Carriers• NADH and NADPH hold e-’s = high energy bonds

– Carry 2 e-’s and a H+ – Precursor = NAD + and NADP +

• Molecules oxidized e-’s released & captured– Dehydrogenase

Cellular Respiration• Aerobic respiration

– Requires O2

– High energy (ATP) yield– Glycolysis

• Common to all paths• Energy from sugar (glucose)

– Citric acid cycle (Kreb’s cycle)• Requires O2

– Oxidative phosphorylation (ETS and Chemiosmosis)

• Requires O2

• Anaerobic respiration– Doesn’t require O2

– Organisms w/o mitochondria– Low energy yield

Step 1: Glycolysis• Aerobic and anaerobic• In the cytoplasm• Starts with:

– Glucose (6C’s)– 2 ATP

• Ends with:– 2 pyruvate (3C’s)

• Important products of this process:– Net 2 ATP

• 4 ATP substrate-level phosphorylation

– 2 NADH

Intermediate Step: ‘Grooming’

• Starts with:– 2 Pyruvate (3C’s)

• High energy product

• Ends with:– 2 Acetyl-CoA (2C’s)

• Important products of this process:– 2 CO2

• Decarboxylation

– 2 NADH

Step 2: Citric Acid Cycle

6 C’s4 C’s

4 C’s

• In the mitochondrial matrix• Starts with:

– 2 Acetyl CoA• Ends with:

– 4 CO2

• Important products of this process:– 2 ATP substrate level

phosphorylation– 6 NADH – 2 FADH2

Step 3: Electron Transport System (ETS)

• In the inner mitochondrial membrane• Starts with:

– 10 NADH (previous steps)– 2 FADH2 (citric acid cycle)– O2

• Ends with:– H2O

• Important products of this process:– H + gradient

Electrons and the Importance of Oxygen• Review

– Electron energy determined by arrangement• e-’s further from the nucleus = more PE• e-’s dropping levels release E

– Oxygen is highly electronegative• Integral protein complexes use a little less energy to ‘hold’ the

electrons• Extra energy transports a H+ across out of the matrix into the

intermembrane space• O2 is the last molecule to accept e-’s to become water

Electrons from reactions in glycolysis and Kreb’s cycle

Step 4: ATP Generation (Chemiosmosis)

• In the inner mitochondrial membrane• Starts with:

– H + gradient

• Ends with:– 32 – 34 ATP• ATP synthase facilitates

A Review of Cellular Respiration

Substrate level phosphorylation

Fermentation

• If no O2 available• Starts with:

– Glucose • Ends with:

– Lactate or– CO2 and ethanol

• Important products of this process:– 2 pyruvate– 2 ATP– 2 NADH/NAD+

• Makes yogurt, bread, alcoholic beverages