…transferring a phosphate group to another molecule = phosphorylation

-- use a little ATP to net a larger amount of kinetic E (work)

…have to make $ to spend $

How do cells do work?• ATP is involved• What organelles are

responsible for energy conversion?

• Converting E from sugar in the presence of O2 = cellular respiration

• …the cell captures E released as ATP

Respiration vs. Breathing

• Exchange of gases… O2 in & CO2 out

• Aerobic energy harvesting = cellular respiration

…more work

requires more O2

Energy extraction by cells…

• Glucose = = C6H12O6 = potential E

• electrons (energy) transfer as carbon - hydrogen bonds break

…hydrogen-oxygen bonds form as water• Transfer of electrons from reactants to products side of

reaction = oxidation-reduction reaction (redox reaction)

3 main stages of cellular respiration

• Glycolysis– Breaking glucose into – a 3-carbon, pyruvate

• Citric acid cycle– Modifies pyruvate

• Oxidative phosphorylation– Uses the E from electron transport chain to

phosphorylate ADP

• Electrons are shuttled by NAD+ – an enzyme, nicotinamide adenine

dinucleotide, that gets reduced (gain of H) to NADH

6.8 Pyruvate is chemically groomed for the citric acid cycle

• The pyruvate formed in glycolysis is transported to the mitochondria, where it is prepared for entry into the citric acid cycle– The first step is removal of a carboxyl group that

forms CO2

– The second is oxidization of the two-carbon compound remaining

– Finally, coenzyme A binds to the two-carbon fragment forming acetyl coenzyme A

Copyright © 2009 Pearson Education, Inc.

Coenzyme A

Pyruvate Acetyl coenzyme A

CoA

NAD+ NADH H+

CO2

13

2

6.10 Most ATP production occurs by oxidative phosphorylation

• Oxidative phosphorylation involves electron transport and chemiosmosis and requires an adequate supply of oxygen– NADH and FADH2 and the inner membrane of

the mitochondria are also involved– A H+ ion gradient formed from all of the redox

reactions of glycolysis and the citric acid cycle provide energy for the synthesis of ATP

Copyright © 2009 Pearson Education, Inc.

ATP

H+

Intermembranespace

O2

H2O

12

Innermitochondrialmembrane

H+NAD+

H+

H+

H+

H+

H+

H+

H+

H+

H+

H+

H+

H+

Mitochondrialmatrix

Electronflow

Electroncarrier

Proteincomplexof electroncarriers

NADH

FADH2FAD

ATPsynthase

PADP +

Chemiosmosis

+ 2

OXIDATIVE PHOSPHORYLATION

Electron Transport Chain

Electron transport chain

• NADH delivers electrons (e-) to a cascade of reactions

…like a slinky moving down a staircase…keeps momentum resulting in a net release of greater E

6.9 The citric acid cycle completes the oxidation of organic molecules, generating many NADH and

FADH2 molecules

• With the help of CoA, the acetyl (two-carbon) compound enters the citric acid cycle– At this point, the acetyl group associates with a four-

carbon molecule forming a six-carbon molecule– The six-carbon molecule then passes through a

series of redox reactions that regenerate the four-carbon molecule (thus the “cycle” designation)

Copyright © 2009 Pearson Education, Inc.

CITRIC ACID CYCLE

NAD+

NADH

3 H+

CO2

3

3

2

CoA

CoA

Acetyl CoA

PADP +ATP

FADH2

FAD

CITRIC ACID CYCLE

CoA

2 carbons enter cycle

Acetyl CoACoA

1Oxaloacetate

1Step

Acetyl CoA stokes the furnace.

CITRIC ACID CYCLE

CoA

2 carbons enter cycle

Acetyl CoACoA

1Oxaloacetate

1Step

Acetyl CoA stokes the furnace.

2

3

NAD+

NADH

CO2

Citrate

ADP +

+ H+

P

Alpha-ketoglutarate

leaves cycle

ATP

NAD+NADH

CO2

+ H+

leaves cycle

Steps –

NADH, ATP, and CO2 are generated

during redox reactions.

2 3

CITRIC ACID CYCLE

CoA

2 carbons enter cycle

Acetyl CoACoA

1Oxaloacetate

1Step

Acetyl CoA stokes the furnace.

2

3

NADH

CO2

Citrate

ADP P

Alpha-ketoglutarate

leaves cycle

ATP

NADH

CO2leaves cycle

Steps –

NADH, ATP, and CO2 are generated

during redox reactions.

2 3

5NAD+

NADH

Malate

+ H+

4FADH2

FAD

Succinate

Steps –

Redox reactions generate FADH2

and NADH.

4 5

NAD+

+ H+

NAD++ H+

How much energy or ATP is produced for each glucose molecule?

Is this system efficient?

• 38 ATPs = 40% of the potential E in glucose

• 60% escapes as heat

• Auto engine converts 25% E from fuel

• Muscle use 10,000,000 ATP per second

Fermentation (animal cells)• Oxidize organic fuel & produce ATP without

oxygen– Anaerobic alternative– Relies on glycolysis (1st step of respiration)

• Only 2 ATPs– Then…converts pyruvate to lactate

– muscle burn– Lactate is recycled by liver

Fermentation (yeast)• Oxidize organic fuel & produce ATP without

oxygen– Anaerobic alternative– Relies on glycolysis (1st step of respiration)

• Only 2 ATPs

– Then…converts pyruvate to ethanol and CO2– Gas bubbles in beer & champhagne, dough to rise– Alcohol is produced as yeast waste…eventually killing ‘em