Chapter 8 An Introduction to Metabolism

Overview: The Energy of Life The living cell is a miniature chemical factory where thousands of reactions occur The cell extracts energy and applies energy to perform work Some organisms even convert energy to light, as in bioluminescence Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

Metabolism Metabolism is the entire collection of an organism’s chemical reactions A metabolic pathway begins with a specific molecule and ends with a product Each step is catalyzed by a specific enzyme Enzyme 1Enzyme 2Enzyme 3 D CB A Reaction 1Reaction 3Reaction 2 Starting molecule Product

Two Types of Metabolism Catabolic pathways release energy by breaking down complex molecules into simpler compounds GLUCOSE CO 2 + H 2 O + ATP Anabolic pathways consume energy to build complex molecules from simpler ones Amino acids Proteins

Energy Energy is the capacity to cause change Types of energy – Kinetic energy is energy associated with motion – Potential energy is energy that matter possesses because of its location or structure Energy can be converted from one form to another

Fig. 8-2 Climbing up converts the kinetic energy of muscle movement to potential energy. A diver has less potential energy in the water than on the platform. Diving converts potential energy to kinetic energy. A diver has more potential energy on the platform than in the water.

The Laws of Energy Transformation Thermodynamics is the study of energy transformations First law of thermodynamics – Energy can be transferred and transformed, but it cannot be created or destroyed Second law of thermodynamics – During every energy transfer or transformation, some energy is unusable, and is often lost as heat (entropy)

Free Energy Free Energy (∆G) - measures a system’s energy that is available to perform work. ∆G = ∆H – T∆S Spontaneous – a process that can occur without the input of energy; ∆G must be a negative value Nonspontaneous – a process that requires the input of energy; ∆G will be a positive value or zero As Biologists, we want to know which rxns of life are spontaneous. These rxns can be harnessed to do work (to drive the nonspontaneous rxns.

When we apply the free energy concept to processes of life and with respect to metabolism, we describe rxns as exergonic or endergonic. An exergonic reaction proceeds with a net release of free energy and is spontaneous Glucose + O 2 CO 2 + H 2 O ∆G = -686 kcal/mol An endergonic reaction absorbs free energy from its surroundings and is nonspontaneous CO 2 + H 2 O Glucose + O 2 ∆G = +686 kcal/mol

3 Main Types of Cellular Work Mechanical Transport Chemical

Fig. 8-8 Phosphate groups Ribose Adenine

Fig. 8-9 Inorganic phosphate Energy Adenosine triphosphate (ATP) Adenosine diphosphate (ADP) P P P PP P + + H2OH2O i

Fig (b) Mechanical work: ATP binds noncovalently to motor proteins, then is hydrolyzed Membrane protein P i ADP + P Solute Solute transported P i VesicleCytoskeletal track Motor protein Protein moved (a) Transport work: ATP phosphorylates transport proteins ATP

Fig P i ADP + Energy from catabolism (exergonic, energy-releasing processes) Energy for cellular work (endergonic, energy-consuming processes) ATP + H2OH2O

Fig Progress of the reaction Products Reactants ∆G < O Transition state Free energy EAEA DC BA D D C C B B A A

Enzyme Inhibitors