Metabolic Pathways and Energy Production

 Metabolism and Cell Structure

 ATP and Energy

 Important Coenzymes in Metabolic Pathways

 Coenzyme NAD⁺

 Coenzyme FAD

 Coenzyme A

Metabolic Pathways

Metabolism involves:

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

Metabolism

 Anabolic reactions that use ATP

energy to build larger molecules.

Metabolic Pathways

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.

S ta g e s o f M e ta b o lis m

Cell Structure

Metabolic reaction occur in specific sites within cells.

Cell Components and Function

ATP and Energy

 In cells, energy is stored in adenosine triphosphate (ATP).

Hydrolysis of ATP



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

ATP ADP + P

_i

+ 7.3 kcal (31 kJ/mole)



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

ADP AMP + P

_i

+ 7.3 kcal (31 kJ/mole)

Hydrolysis of ATP to ADP and ADP to AMP

ATP and Muscle Contraction

 Muscle fibers contains filaments of actin and myosin.

 When a nerve impulse increases Ca⁺², the filaments slide closer together to contract muscle.

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

 As Ca⁺² and ATP decrease, the filaments return to the relaxed position.

A T P a n d M u sc le C o n tr a ct io n

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^-

Reduction

NAD⁺ + 2H⁺ + 2e^- NADH + H⁺

Structure of Coenzyme NAD

⁺

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

 NAD+ reduces to NADH when the

nicotinamide group accepts 2H+ and 2e-

Coenzyme FAD

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

Oxidation

—CH₂—CH₂— —CH=CH— + 2H⁺ + 2e^-

Reduction

FAD + 2H⁺ + 2e^- FADH₂

Structure of Coenzyme FAD

 FAD (flavin adenine dinucleotide)

contains ADP and riboflavin (vitamin B₂)

 FAD reduces to

FADH₂ when flavin accepts 2H⁺ and 2e^-

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