Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Concept 8.1: An organism’s metabolism transforms matter and energy, subject to the laws of thermodynamics Metabolism is the totality of an organism’s chemical reactions including matter and energy.

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Organization of the Chemistry of Life into Metabolic Pathways A metabolic pathway is a series of chemical reactions that begins with a specific molecule and ends with a product Each step is catalyzed by a specific enzyme Enzyme 1 AB Reaction 1 Enzyme 2 C Reaction 2 Enzyme 3 D Reaction 3 Product Starting molecule

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Metabolic Pathways: Catabolic and Anabolic Pathways 1- Catabolic pathways breakdown complex molecules to form simpler molecules & liberate energy that is available to the cell. e.g: in cellular respiration: Glucose breaks down to CO 2 and H 2 O & energy is released. – some of the released energy is saved as ATP and used by the cell as energy currency. – most of the energy is released as heat energy

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Metabolic Pathways: Catabolic and Anabolic Pathways 2- Anabolic pathways consume energy to build complex molecules from simpler ones Examples: – making sugars from CO 2 and H 2 O – making starch from glucose – making proteins from amino acids. – making fats from fatty acids and glycerol

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Forms of Energy Energy is the capacity to cause change. Energy exists in various forms.

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Kinetic energy is energy associated with motion. Potential energy is: – energy that matter possesses because of its location or structure. – It’s energy at rest, but has the potential to do work. Forms of Energy

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Energy can be converted from one form to another watch?v=vl4g7T5gw1M Energy conversion!!!! Wait, I can explain that.

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Energy can be converted from one form to another Energy conversion!!!! What’s going on up there?

On the platform, the diver has more potential energy. Diving converts potential energy to kinetic energy. Climbing up converts kinetic energy of muscle movement to potential energy. In the water, the diver has less potential energy. Energy can be converted from one form to another

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings The First Law of Thermodynamics Thermodynamics is the study of energy transformations According to the first law of thermodynamics, the energy of the universe is constant – Energy can be transferred and transformed – Energy cannot be created or destroyed The first law is also called the principle of conservation of energy.

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings The Second Law of Thermodynamics During every energy transfer or transformation, some energy is unusable, often lost as heat According to the second law of thermodynamics, every energy transfer or transformation increases the entropy (disorder) of the universe. Living cells unavoidably convert organized forms of energy to heat Chemical energy Heat CO 2 First law of thermodynamicsSecond law of thermodynamics H2OH2O

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Enzymes speed up metabolic reactions by lowering energy barriers A catalyst is a chemical agent that speeds up a reaction without being consumed by the reaction An enzyme is a catalytic protein

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Enzymes

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings The Activation Energy Barrier Every chemical reaction between molecules involves bond breaking and bond forming The initial energy needed to start a chemical reaction is called the free energy of activation, or activation energy (E A ) Activation energy is often supplied in the form of heat from the surroundings

LE 8-14 Transition state CD A B EAEA Products CD A B  G < O Progress of the reaction Reactants C D A B Free energy

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Enzymes lower the activation energy of a reaction Enzymes lower the activation energy of a reaction, increase the speed of a reaction (millions of reactions per minute!) Enzymes do not affect the change in free-energy (∆G).

Enzymes lower the activation energy of a reaction Course of reaction without enzyme E A without enzyme  G is unaffected by enzyme Progress of the reaction Free energy E A with enzyme is lower Course of reaction with enzyme Reactants Products

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Figure 3.12 Activation Energy Initiates Reactions

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Substrate Specificity of Enzymes The reactant that an enzyme acts on is called the enzyme’s substrate The enzyme binds to its substrate, forming an enzyme-substrate complex The active site is the region on the enzyme where the substrate binds Induced fit of a substrate brings chemical groups of the active site into positions that enhance their ability to catalyze the reaction.

LE 8-16 Substrate Active site Enzyme Enzyme-substrate complex