Metabolic Pathways Metabolism and Cell Structure ATP and

Metabolic Pathways § Metabolism and Cell Structure § ATP and Energy § Important Coenzymes in Metabolic Pathways § Coenzyme NAD+ § Coenzyme FAD § Coenzyme A

Metabolism involves: n Catabolic reactions that break down large, complex molecules to provide energy and smaller molecules. n Anabolic reactions that use ATP energy to build larger molecules.

Metabolic Pathways

Stages of Metabolism Catabolic reactions are organized as stages: n n n 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 twoand three-carbon compounds. In Stage 3, compounds are oxidized in the citric acid cycle to provide energy.

Stages of Metabolism

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 n The hydrolysis of ATP to ADP releases 7. 3 kcal (31 k. J/mole). ATP n ADP + Pi + 7. 3 kcal (31 k. J/mole) The hydrolysis of ADP to AMP releases 7. 3 kcal (31 k. J/mole). ADP AMP + Pi + 7. 3 kcal (31 k. J/mole)

Hydrolysis of ATP to ADP and ADP to AMP

ATP and Muscle Contraction n n 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.

ATP and Muscle Contraction

Coenzyme NAD+ n n In cells, the oxidation of compounds provides 2 H as 2 H+ and 2 e- that reduce coenzymes. NAD+ (Nicotinamide Adenine Dinucleotide) participates in reactions that produce a carbon-oxygen double bond (C=O). Oxidation O || CH 3—CH 2—OH CH 3—C—H + 2 H+ + 2 e. Reduction NAD+ + 2 H+ + 2 e- NADH + H+

Structure of Coenzyme NAD+ n n NAD+ (nicotinamide adenine dinucleotide) contains ADP, ribose, and nicotinamide. NAD+ reduces to NADH when the nicotinamide group accepts 2 H+ and 2 e-

Coenzyme FAD n FAD participates in reactions that produce a carbon-carbon double bond (C=C). Oxidation —CH 2— Reduction FAD + 2 H+ + 2 e- —CH=CH— + 2 H+ + 2 e- FADH 2

Structure of Coenzyme FAD n FAD (flavin adenine dinucleotide) contains ADP and riboflavin (vitamin B 2) n FAD reduces to FADH 2 when flavin accepts 2 H+ and 2 e-

Coenzyme A n Co. A activates acyl groups such as the two-carbon acetyl group for transfer. O O || || CH 3—C— + HS—Co. A CH 3—C—S—Co. A