Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings AN INTRODUCTION TO METABOLISM

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Metabolism, transforming matter and energy Metabolism – all of the chemical reactions in an organism – These reactions are ordered into metabolic pathways

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Metabolic Pathways A metabolic pathway begins with a specific molecule and ends with a product living things acquire energy by breaking the chemical bonds of carbohydrates and other molecules and transferring the energy of these bonds to ATP

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Catabolic pathways (“cata” means down) – release energy by breaking down complex molecules into simpler compounds Anabolic pathways( “ana” means up) – consume energy to build complex molecules from simpler ones The energy released from catabolic pathways drives anabolic pathways The two pathways

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Anabolic and Catabolic Pathways

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Pathways and Energy Energy Drives these processes Bond breaking and energy transfers are aided by enzymes What is Energy?...

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Forms of Energy Energy – The ability to do work – Exists in two states

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Kinetic energy (kinet means movement) – The energy of motion, of matter that is moving Potential energy (stored energy) – objects that are not yet moving but have the capacity to do so. Living organisms transform potential energy to kinetic energy as they do work. Animation: Energy Concepts Animation: Energy Concepts The Forms of Energy

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings The Laws of Energy Transformation Thermodynamics – the study of energy transformations Energy exits in many forms All other forms of energy can be converted into heat, so the most convenient way to measure energy is in terms of heat. Thermodynamics means heat changes.

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Energy Flow/Changes in energy Begins with the sun Photosynthetic organisms capture a fraction of this energy They produce complex molecules (sugars) The sugars have potential energy due to the arrangement of the atoms This potential energy, in the form of chemical energy, does the work in cells Making and breaking these bonds is a chemical reaction and requires energy

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Laws of Thermodynamics govern all energy changes in the universe The First Law of Thermodynamics – Energy can change from one state to another – Energy cannot be created or destroyed The total energy of the universe is constant During each conversion, some of the energy dissipates into the environment as Heat Energy heat energy is incapable of doing the work of cells

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings The Second Law of Thermodynamics The disorder in a closed system like the universe is continuously increasing. – Disorder is more likely than order

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Entropy –is a measure of disorder or randomness Everything done in nature increases the entropy of the universe when the earth was formed it held all the potential energy it will ever have. It has become progressively more disordered ever since. Second Law of Thermodynamics

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Where does energy go if it cannot be destroyed? It is converted to heat All energy conversions generate some heat. Heat is the least ordered form of energy.

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Chemical Reactions Reactants – molecules you start with (or substrates) Products – molecules you end up with after the reaction is over A reaction is more likely to occur if it releases energy than if it needs to have energy supplied

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Exergonic and Endergonic Reactions in Metabolism An exergonic reaction proceeds with a net release of free energy and is spontaneous – Products contain less energy than the reactants An endergonic reaction absorbs free energy from its surroundings and is nonspontaneous – Products contain more energy than the reactants

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Exergonic and Endergonic reactions Amount of energy required Endergonic reaction Amount of energy released Exergonic reaction

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Activation Energy The energy required to start a chemical reaction – It is like a chemical nudge If the activation energy is lowered, this will make an exergonic/endergonic reaction happen more quickly.

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 Hydrolysis of sucrose by the enzyme sucrase is an example of an enzyme-catalyzed reaction Enzymes are biological catalysts

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings PowerPoint Lectures for Biology, Seventh Edition Neil Campbell and Jane Reece Lectures by Chris Romero LE 8-15 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 Enzyme Activity substrateSubstrate bonds to active site. Induced fit. Forms an enzyme substrate complex Substrate is converted to products Products are released Enzyme is available with empty active site

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Substrate Specificity of Enzymes Protein enzymes have characteristic three-dimensional shapes. The specificity of an enzyme for a particular substrate is determined by this shape. The substrate attaches at the enzyme’s active site, a groove found on the surface of the enzyme that has a shape complementary to the substrate. The enzyme binds to its substrate, forming an enzyme- substrate complex Induced fit of a substrate brings chemical groups of the active site into positions that enhance their ability to catalyze the reaction

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Factors affecting enzyme activity Temperature – If the temp. increases it weakens the bond that determines the enzymes shape, and the enzyme is denatured. pH – Structural bonds are sensitive to H+ concentration – Most function within an optimal pH range

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings LE 8-18 Optimal temperature for typical human enzyme Optimal temperature for enzyme of thermophilic (heat-tolerant bacteria) Temperature (°C) Optimal temperature for two enzymes Rate of reaction Optimal pH for pepsin (stomach enzyme) Optimal pH for trypsin Protein degrading enzyme pH Optimal pH for two enzymes 0 Rate of reaction

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Cofactors-nonprotein enzyme helpers Cofactors are inorganic helpers – Zinc, iron or copper ions Coenzymes are organic helpers – Vitamins or made from vitamins B6 for example

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings How Cells Regulate Enzymes Enzymes have shapes that can be altered – Allosteric enzymes Inhibitors will interfere with an enzymes activity – Toxins and poisons are examples of when this would be harmful – Some drugs and antibiotics inhibit enzymes that create too much cholesterol, or prohibit the forming of cell walls in bacteria – Feedback inhibition controls metabolic pathways when an enzymes product acts as an inhibitor. This way it will stop synthesizing more of an unnecessary product.

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Types of Enzyme Inhibitors Competitive inhibitors bind to the active site of an enzyme, competing with the substrate Noncompetitive inhibitors bind to another part of an enzyme, causing the enzyme to change shape and making the active site less effective

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings ATP: The Energy Currency of the Cell How does the cell use energy from the sun or the potential energy stored in molecules to power its activities? The energy sources stored in cells cannot be used directly to run a cell To be useful this stored energy must be converted to a source of energy that a cell can use ATP is the energy “currency” of the cell

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings The Cells energy comes from ATP The phosphates are poised to push apart due to their negative electrical charges. Therefore they are chemically reactive bonds.

LE 8-8 Phosphate groups Ribose Adenine Structure of ATP Nitrogenous base sugar 1. The bonds between the phosphate groups of ATP’s tail can be broken by hydrolysis Energy is released from ATP when the terminal phosphate bond is broken Adenosine

LE 8-9 Adenosine triphosphate (ATP) Energy PP P PP P i Adenosine diphosphate (ADP) Inorganic phosphate H2OH2O + + ATP is hydrolyzed (water) to ADP and an inorganic phosphate molecule, releasing energy When energy is released ATP is converted to ADP.

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings ATP and Cellular Work The hydrolysis of ATP is an exergonic reaction The phosphate from ATP that is lost will be transferred to some other molecule – This becomes an endergonic reaction This transfer is called phosphorylation. This process energizes molecules and allows them to do work.

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings How ATP powers cellular work

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings How ATP powers cellular work Three main types – Chemical Reactant molecules synthesize product molecules (endergonic) – Mechanical Contraction of muscle cells by transfer of phosphate groups to motor proteins causing proteins to change shape – Transport Phosphorylating membrane proteins – transport materials across membranes

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings The Regeneration of ATP ATP is a renewable resource that cells regenerate EX. Glucose breakdown during cellular respiration is used to regenerate ATP from ADP

LE 8-12 P i ADP Energy for cellular work (endergonic, energy- consuming processes) Energy from catabolism (exergonic, energy- yielding processes) ATP + The ATP Cycle A working cell may consume and regenerate 10 million ATP molecules each second.