Introduction to Metabolism How the Universe Really Works

What is Energy? Capacity to do work Capacity to do work Forms of energy Forms of energy Electrical Electrical Mechanical Mechanical Chemical Chemical Light Light Heat Heat

What is Energy? Capacity to do work Capacity to do work Forms of energy Forms of energy Potential energy Potential energy Kinetic energy Kinetic energy

Kinetic and potential energy: dam Stored Water = Potential Energy Stored Water = Potential Energy Moving Water = Kinetic Energy Moving Water = Kinetic Energy

Kinetic and potential energy: cheetah at rest and running Cheetah resting =Cheetah running = Potential EnergyKinetic Energy

Energy can be converted from one form to another. Energy can be converted from one form to another. As the boy climbs the ladder to the top of the slide he is converting his kinetic energy to potential energy. As the boy climbs the ladder to the top of the slide he is converting his kinetic energy to potential energy. As he slides down, the potential energy is converted back to kinetic energy. As he slides down, the potential energy is converted back to kinetic energy. It was the potential energy in the food he had eaten earlier that provided the energy that permitted him to climb up initially. It was the potential energy in the food he had eaten earlier that provided the energy that permitted him to climb up initially. Fig. 6.2

One-Way Flow of Energy The sun is life’s primary energy source The sun is life’s primary energy source Producers trap energy from the sun and convert it into chemical bond energy Producers trap energy from the sun and convert it into chemical bond energy All organisms use the energy stored in the bonds of organic compounds to do work All organisms use the energy stored in the bonds of organic compounds to do work

What Can Cells Do with Energy? Energy inputs become coupled to energy-requiring processes Energy inputs become coupled to energy-requiring processes Cells use energy for: Cells use energy for: Chemical work Chemical work Mechanical work Mechanical work Electrochemical work Electrochemical work

Energy Relationships ATP BIOSYNTHETIC PATHWAYS (ANABOLIC) ENERGY INPUT DEGRADATIVE PATHWAYS (CATABOLIC) energy-poor products such as carbon dioxide, water large energy-rich molecules (fats, complex carbohydrates, proteins, nucleic acids) simple organic compounds simple sugars, amino acids, fatty acids, nucleotides ADP + P i

Thermodynamics Thermodynamics is the study of energy transformations. Thermodynamics is the study of energy transformations. system indicates the matter under study and the surroundings are everything system indicates the matter under study and the surroundings are everything closed system is isolated from its surroundings. closed system is isolated from its surroundings. In an open system energy (and often matter) can be transferred between the system and surroundings. In an open system energy (and often matter) can be transferred between the system and surroundings. Organisms are open systems. Organisms are open systems. They absorb energy - light or chemical energy in organic molecules - and release heat and metabolic waste products They absorb energy - light or chemical energy in organic molecules - and release heat and metabolic waste products

First Law of Thermodynamics The total amount of energy in the universe remains constant The total amount of energy in the universe remains constant Energy can undergo conversions from one form to another, but it cannot be created or destroyed Energy can undergo conversions from one form to another, but it cannot be created or destroyed

Second Law of Thermodynamics No energy conversion is ever 100 percent efficient No energy conversion is ever 100 percent efficient The total amount of energy is flowing from high-energy forms to forms lower in energy The total amount of energy is flowing from high-energy forms to forms lower in energy

Two laws of thermodynamics Two laws of thermodynamics Conversion of energy from chemical potential to kinetic mechanical energy. Some energy is lost to heat.

Entropy Measure of degree of disorder in a system Measure of degree of disorder in a system The world of life can resist the flow toward maximum entropy only because it is resupplied with energy from the sun The world of life can resist the flow toward maximum entropy only because it is resupplied with energy from the sun

Free energy can be thought of as a measure of the stability of a system. Free energy can be thought of as a measure of the stability of a system. Systems that are high in free energy - compressed springs, separated charges - are unstable and tend to move toward a more stable state - one with less free energy. Systems that are high in free energy - compressed springs, separated charges - are unstable and tend to move toward a more stable state - one with less free energy. Systems that tend to change spontaneously are those that have high energy, low entropy, or both. Systems that tend to change spontaneously are those that have high energy, low entropy, or both. In any spontaneous process, the free energy of a system decreases. In any spontaneous process, the free energy of a system decreases. Free Energy

Energy changes in exergonic and endergonic reactions Energy changes in exergonic and endergonic reactions

The Math We can represent this change in free energy from the start of a process until its finish by: We can represent this change in free energy from the start of a process until its finish by: delta G = G final state - G starting state delta G = G final state - G starting state Or delta G = delta H - T delta S Or delta G = delta H - T delta S For a system to be spontaneous, the system must either give up energy (decrease in H), give up order (decrease in S), or both. For a system to be spontaneous, the system must either give up energy (decrease in H), give up order (decrease in S), or both. Delta G must be negative. Delta G must be negative. The greater the decrease in free energy, the greater the maximum amount of work that a spontaneous process can perform. The greater the decrease in free energy, the greater the maximum amount of work that a spontaneous process can perform. Nature runs “downhill”. Nature runs “downhill”.

Still Calculating The magnitude of delta G for an exergonic reaction is the maximum amount of work the reaction can perform. The magnitude of delta G for an exergonic reaction is the maximum amount of work the reaction can perform. For the overall reaction of cellular respiration: For the overall reaction of cellular respiration: C 6 H 12 O 6 + 6O 2 -> 6CO 2 + 6H 2 O C 6 H 12 O 6 + 6O 2 -> 6CO 2 + 6H 2 O delta G = -686 kcal/mol delta G = -686 kcal/mol Through this reaction 686 kcal have been made available to do work in the cell. Through this reaction 686 kcal have been made available to do work in the cell. The products have 686 kcal less energy than the reactants The products have 686 kcal less energy than the reactants

Endergonic Reactions Energy input required Energy input required Product has more energy than starting substances Product has more energy than starting substances product with more energy (plus by-products 60 2 and 6H 2 O) ENERGY IN 612

Exergonic Reactions Energy is released Energy is released Products have less energy than starting substance Products have less energy than starting substance ENERGY OUT energy-rich starting substance products with less energy 66

Participants in Metabolic Pathways Energy Carriers Enzymes Cofactors Substrates Substrates Intermediates Intermediates End products End products