 Types of Chemical transformations within the cells  Organisms Transform Energy  Laws of Thermodynamics  Endergonic and Exergonic Reactions  Metabolism  ATP and Energy  Important Coenzymes in Metabolic Pathways  Coenzyme NAD +  Coenzyme FAD  Coenzyme A Bioenergetics and Metabolic Pathways Bioenergetics and Metabolic Pathways

General Types of Chemical Transformation

Oxidation-Reduction Reduced: Reduced: – Molecule/atom gains electrons. Reducing agent: Reducing agent: – Molecule/atom that donates electrons. Oxidized: Oxidized: – Molecule/atom loses electrons. Oxidizing agent: Oxidizing agent: – Molecule/atom that accepts electrons. Oxidation and Reduction are always coupled reactions.

May involve the transfer of H+ rather than free electrons. Molecules that serve important roles in the transfer of hydrogen are NAD and FAD. – Coenzymes that function as hydrogen carriers. Oxidation-Reduction

Organisms Transform Energy  Thermodynamics:  Thermodynamics: Study of energy transformations.  Bioenergetics:  Bioenergetics: Study of the transformation of energy in living organisms.  Energy:  Energy: Capacity to do work.  Kinetic energy:  Kinetic energy: Energy in the process of doing work (energy of motion). For example:  Heat (thermal energy) is kinetic energy expressed in random movement of molecules.  Light energy from the sun is kinetic energy which powers photosynthesis.

 Potential energy: locationstructure  Potential energy: Energy that matter possesses because of its location or structure (energy of position). For example:  In the earth's gravitational field, an object on a hill or water behind a dam have potential energy.  Chemical energy is potential energy stored in molecules because of the structural arrangement of the nuclei and electrons in its atoms. Organisms Transform Energy

 First Law:  First Law: (Conservation of energy)  Energy can be transferred or transformed but neither created nor destroyed. (energy of the universe is constant).  Second Law:  Efficiencies of energy transformation never equal 100%.  Therefore, all processes lose energy, typically as heat, and are not reversible unless the system is open & the lost energy is resupplied from the environment.  Conversion to heat is the ultimate fate of chemical energy. Laws of Thermodynamics

Not all of a system's energy is available to do work. The amount of energy that is available to do work is described by the concept of free energy. Free energy (G) is related to the system's total energy (H) and its entropy (S) in the following way: G = H – TS where: G = free energy (energy available to do work) H = enthalpy or total energy T = absolute temperature in °K (K= °C + 273) S = entropy Free Energy: A Criterion For Spontaneous Change

Endergonic and Exergonic Reactions  Endergonic : – Reactions require an input of energy to make reaction. – Products must contain more free energy than reactants. Exergonic: Exergonic: Reactions convert molecules with more free energy to molecules with less. Release energy in the form of heat. Heat is measured in calories. Reactions can be classified based upon their free energy changes:

If a chemical process is exergonic, the reverse process must be endergonic. For example:Cellular respiration C 6 H 12 O O 2 6 CO H 2 O ∆G = –686 kcal/mol  For each mole (180 g) of glucose oxidized in the exergonic process of cellular respiration 686 kcal (kilocalorie) are released (∆G = – 686 kcal/mol )  To produce a mole of glucose, the endergonic process of photosynthesis requires energy input of 686 kcal (∆G = or +686 kcal/mol).

Cellular respiration Photosynthesis C 6 H 12 O O 2 6 CO H 2 O

Exergonic Reaction Endergonic Reaction Chemical products have less free energy than the reactant molecules. Products store more free energy than reactants. Reaction is energetically downhill.Reaction is energetically uphill. Spontaneous reaction.Non-spontaneous reaction (requires energy input). ∆G is negative.∆G is positive. –∆G is the maximum amount of work the reaction can perform +∆G is the minimum amount of work required to drive the reaction.

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.

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.

Stages of Metabolism

 A cell does three main kinds of work:  Mechanical work, beating of cilia, contraction of muscle cells, and movement of chromosomes  Transport work, pumping substances across membranes against the direction of spontaneous movement  Chemical work, driving endergonic reactions such as the synthesis of polymers from monomers.  In most cases, the immediate source of energy that powers cellular work is ATP. ATP powers cellular work by coupling exergonic reactions to endergonic reactions

 ATP (adenosine triphosphate): Nucleotide with unstable phosphate bonds that the cell hydrolyzed for energy to drive endergonic reactions.  ATP consists of :  Adenine, a nitrogenous base.  Ribose, a five-carbon sugar.  Chain of three phosphate groups The Structure and Hydrolysis of ATP

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

ATP and Muscle Contraction

Coenzymes  Organic molecules that enhances the action of an enzyme, "helper molecules". They carry and transfer electrons, atoms, or molecules through the reaction.  Coenzymes can be used by a number of different enzymes (non-specific).  A number of the water-soluble vitamins such as vitamins B1, B2, B5 and B6 serve as coenzymes.  In metabolism, coenzymes play a role in group- transfer reactions (Coenzyme A, CoA) and oxidation- reduction reactions (Coenzyme NAD + )

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 Oxidation O || CH 3 —CH 2 —OH CH 3 —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 H+ and 2e-

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

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

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