Chapter 6 Metabolism

6.1 Energy and Metabolism

Energy: the capacity to do work Chemical reactions in a cell require a transfer of energy Endergonic reactions have products with more energy Exergonic reactions have products with less energy

6.2 Potential, Kinetic, Free and Activation

The energy that fuels most life on Earth comes from the sun Kinetic energy: the energy of motion Potential energy: chemical energy is stored in bonds The change in bond energy minus entropy contribute to a molecule’s free energy (energy available to do work) Activation energy: minimum energy required to get a chemical reaction started –all reactions require some input

6.3 Laws of Thermodynamics

First law of thermodynamics: energy cannot be created or destroyed Second law of thermodynamics: energy disperses spontaneously Entropy: measure of how much the energy of a system is dispersed

With each energy transfer, some energy A Energy In Sunlight reaches environments on Earth. Producers in those environments capture some of its energy and convert it to other forms that can drive cellular work. producers B Some of the energy captured by producers ends up in the tissues of consumers. CONSUMERS Figure 5.3 {Animated} Energy flows from the environment into living organisms, and then back to the environment. The flow drives a cycling of materials among producers and consumers. C Energy Out With each energy transfer, some energy escapes into the environment, mainly as heat. Living things do not use heat to drive cellular work, so energy flows through the world of life in one direction overall.

6.4 ATP

ATP (adenosine triphosphate) functions as a cofactor in many reactions Bonds between phosphate groups hold a lot of energy When a phosphate group is transferred via the process of phosphorylation, energy is transferred along with it

Recycling ATP ATP/ADP cycle: cells regenerate ATP ADP (diphosphate) forms when a phosphate group is removed from ATP ATP forms as ADP gains a phosphate group

6.5 Enzymes

Metabolism requires enzymes In a process called catalysis, an enzyme reduces the activation energy of a reaction Enzymes help bring reactants to a transition state by orienting substrates

Enzymes recognizes specific substrates (reactants) that are altered in specific ways Active site: part of the enzyme where substrates binds and reaction occurs

substrate enzyme enzyme enzyme enzyme product enzyme enzyme

Metabolic Pathways

Enzyme regulation Series of enzyme-mediated reactions cells build organic molecules Regulatory molecules bind directly to an enzyme’s active site Allosteric regulator alters the shape of an enzyme in a way that enhances or inhibits its function