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Bioenergetics and Introduction to Metabolism -3

The transfer and utilization of energy in biologic systems

Lippincott chapter 6

O2

CO2

ATP is not a long term storage form of energy

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Approximate glucose uptake and ATP turnover by various tissues

Tissue Approximate O2consumption

mole/ day

Equivalent glucose

mole/ day

ATP turnover mole/day

Brain 3.4 0.57 20.4Heart 1.9 0.32 11.4Kidney 2.9 0.49 17.4Liver 3.6 0.6 21.6Muscle 3.3 0.54 19.8Total 15.1 2.52 90.6

• Based on O2 consumption• Assuming glucose is the fuel used

C6H12O6 + 6O2 6CO2 + 6H2O + 36ATP

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Caloric value and free energy changes for complete oxidation of some fuels

Compound ΔGºkcal/mol

Molecular weight

Caloric value

Glucose 686 180 3.8

Palmitate 2380 256 9.3

Glycine 234 75 3.1

Glucose + O2 → CO2 + H2O 686 kcal/mole

Other nucleotide triphosphates

• GTP, UTP, CTP• Synthesized from ATP

ATP + GDP ADP + GTP– GTP in protein synthesis– UTP in polysaccharide synthesis– CTP in phospholipids synthesis

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UDP- is a carrier of activated sugar

UDP-glucose in glycogen synthesis

• Glycogen synthesis from glucose requires energy– Glucose Glycogen + H2O

• UDP-glucoseis the activated carrier of glucoseUTP + Glucose 1-P UDP-Glc + PPi

UDP-Glc + Glycogen(n) UDP + Glycogen(n+1)

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Acetyl Coenzyme A is a high energy compound

• Coenzyme A is a universal carrier of Acyl groups• Forms thioester bond with carboxyl group

O O װ װ

• RC~S-CoA CH3C~S-CoA

Acyl CoA Acetyl CoA

Acetyl CoA + H2O Acetate + CoA ΔGº = -7.5kcal

Acetylcholine + H2O Acetate + Choline ΔGº = -3 kcal

Adenine

Ribose

2 phosphate

s

Pantothenic acid

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Coenzyme A is a donor of Acyl groups

Acetate + Choline Acetylcholine + H2O ΔGº = +3 kcal

Acetyl CoA + H2O Acetate + CoA ΔGº = -7.5kcal

Acetyl CoA + Choline Acetylcholine + COA

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Oxidation of fuel molecules occurs in two stages

• Oxidation: Loss of electrons• Reduction: Gain of electrons• Aerobic oxidation: Transfer of electrons to

oxygen

- 1st stage: Transfer of e to electron carrier- 2nd stage: Transfer of e to oxygen

Fuel electron carrier Oxygen

A•• A

Carrier carrier••

O•• O

ADP + PiATP

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Electron carriers• Electron carriers are dinucleotides• Nucleotide is formed from

Phosphate- ribose- Nitrogenous base• Two nucleotides connected through

phosphate Dinucleotide • One of the bases is Adenine

• NAD+: Nicotinamide Adenine Dinucleotide• FAD: Flavin Adenine Dinucleotid

Base Ribose

P PRibose Adenine

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Reduction potential

• A- + B A + B-Type of reactionWhat determine the direction of the reaction?

• A+ + B+++ A++ + B++

Type of reactionWhat determine the direction of the reaction?

P P

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Reduction potential and direction of the reaction

A + B- A- + B ΔGº = -veB oxidized formB- reduced form

A

A-

B

B-

V

Redox couple

Reduction potential and direction of the reaction

H+ + X- H2 + X ΔGº = -veX oxidized formX- reduced form

X

X-

H+

V

Redox couple

H2

X- has higher tendency to loose electrons than H2 does

Negative reduction potential

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Reductionpotential: Ability to acceptelectronsOxidized + e- Reduced ΔEº

Succinate α ketoglutarate - 0.67

Acetate Acetaldehyde - 0.60

NAD+ NADH - 0.32

Acetaldehyde Ethanol - 0.20

Pyruvate Lactate - 0.19

Fumarate Succinate + 0.03

Cytochrome+3 Cytochrome+2 + 0.22

oxygen water + 0.82

Calculation of ΔGº from ΔEº• ΔGº = - nF ΔEº

– F = Farady constant = 23.06 kcal/ Volt

• Calculate ΔGº of the following reaction

NADH + 1/2O2 NAD+ + H2O

NADH NAD+ + 2e- ΔEº = +0.32O + 2e- O2- ΔEº = +0.82

ΔGº = - 52.6 kcal/mol

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Degradation and synthesis occur in a stepwise manner

A GNot a single step but a sequence of steps

A B C D E F G

Called metabolic pathwayAnabolic or Catabolic