1 23.1 Metabolism and Cell Structure 23.2 ATP and Energy 23.3 Important Coenzymes in Metabolic...

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23.1 Metabolism and Cell Structure 23.2 ATP and Energy23.3 Important Coenzymes in Metabolic Pathways

Chapter 23 Metabolic Pathways for Carbohydrates

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Metabolism involves: Catabolic reactions

that break down large, complex molecules to provide energy and smaller molecules.

Anabolic reactions that use ATP energy to build larger molecules.

Metabolism

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Stages of Metabolism

Catabolic reactions are organized as stages: In Stage 1, digestion breaks down large

molecules into smaller ones that enter the bloodstream.

In Stage 2, molecules in the cells are broken down to two- and three-carbon compounds.

In Stage 3, compounds are oxidized in the citric acid cycle to provide energy.

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Stages of Metabolism

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Cell Structure Metabolic reaction occur in specific sites

within cells.

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Cell Components and Function

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ATP and Energy In cells, energy is stored in adenosine triphosphate

(ATP).

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Hydrolysis of ATP

The hydrolysis of ATP to ADP releases 7.3 kcal (31 kJ/mole). ATP ADP + Pi + 7.3 kcal (31 kJ/mole)

The hydrolysis of ADP to AMP releases 7.3 kcal (31 kJ/mole). ADP AMP + Pi + 7.3 kcal (31 kJ/mole)

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Hydrolysis of ATP to ADP and ADP to AMP

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ATP and Muscle Contraction Muscle fibers contains filaments of actin and

myosin. When a nerve impulse increases Ca2+, the

filaments slide closer together to contract muscle.

The hydrolysis of ATP in muscle provides the energy for contraction.

As Ca2+ and ATP decrease, the filaments return to the relaxed position.

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ATP and Muscle Contraction

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Coenzyme NAD+

In cells, the oxidation of compounds provides 2H as 2H+ and 2e- that reduce coenzymes.

NAD+ (nicotinamide adenine dinucleotide) participates in reactions that produce a carbon-oxygen double bond (C=O).Oxidation O

||CH3—CH2—OH CH3—C—H + 2H+ + 2e-

ReductionNAD+ + 2H+ + 2e- NADH + H+

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Structure of Coenzyme NAD+

NAD+ (nicotinamide adenine dinucleotide) contains ADP, ribose, and nicotinamide.

NAD+ reduces to NADH when the nicotinamide group accepts H+ and 2e-.

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Coenzyme FAD

FAD participates in reactions that produce a carbon-carbon double bond (C=C).

Oxidation —CH2—CH2— —CH=CH— + 2H+ + 2e-

ReductionFAD + 2H+ + 2e- FADH2

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Structure of Coenzyme FAD FAD (flavin

adenine dinucleotide) contains ADP and riboflavin (vitamin B2).

FAD reduces to FADH2 when flavin accepts 2H+ and 2e-.

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Coenzyme A CoA activates acyl groups such as the two-carbon

acetyl group for transfer. O O || ||

CH3—C— + HS—CoA CH3—C—S—CoA