Biology, 9th ed,Sylvia Mader Chapter 06 Chapter 06 Metabolism Metabolism

Outline Forms of Energy Metabolic Reactions Metabolic Pathways Laws of Thermodynamics Metabolic Reactions ATP Metabolic Pathways Energy of Activation Enzymes

Forms of Energy Kinetic: Potential: Energy of motion Mechanical Stored energy Chemical

Energy Energy is capacity to do work; cells must continually use energy to do biological work. Kinetic energy is energy of motion; all moving objects have kinetic energy. Potential energy is stored energy. Ex. Water behind a dam has potential energy that can be converted to kinetic energy.

Flow of Energy

Laws of Thermodynamics First Law: Law of conservation of energy Energy cannot be created or destroyed, but Energy CAN be changed from one form to another Second Law: Law of ENTROPY When energy is changed from one form to another, there is a loss of usable energy Waste energy goes to increase disorder

Laws of Thermodynamics Second law: (Law of ENTROPY) Energy conversions result in heat and therefore the entropy of the universe is always increasing. It takes a constant input of usable energy from the food you eat to keep you organized.

Carbohydrate Synthesis

Carbohydrate Metabolism

Cells & Energy

Metabolic Reactions and Energy Transformations Biology, 9th ed,Sylvia Mader Chapter 06 Metabolic Reactions and Energy Transformations Metabolism Metabolism: Sum of cellular chemical reactions in cell Reactants participate in reaction Products form as result of reaction Free energy is the amount of energy available to perform work Exergonic Reactions - Products have less free energy than reactants Endergonic Reactions - Products have more free energy than reactants Animation

Living systems require free energy and matter to maintain order, grow and reproduce.

Gibbs Free Energy (G) “Available energy” Energy that can do work under cellular conditions Concept from Thermodynamics

Life requires a highly ordered system.

Order is maintained by constant input of free energy into the system.

Loss of order or free energy flow results in death.

An organism’s metabolism transforms matter and energy, subject to the laws of thermodynamics.

Thermodynamics: the laws of energy transformations.

The First Law of Thermodynamics According to the first law of thermodynamics: Energy cannot be created or destroyed Energy can be transferred and transformed

The Second Law of Thermodynamics: spontaneous changes that do not require outside energy increase the entropy, or disorder, of the universe.

Increased disorder and entropy are offset by biological processes that maintain or increase order.

Metabolic Reactions and Energy Transformations Catabolic pathways release energy by breaking down complex molecules to simpler compounds. Ex: Cellular respiration - degrades glucose to carbon dioxide & water; provides energy for cellular work. Anabolic pathways consume energy to build complicated molecules from simpler ones. Ex: Photosynthesis - synthesizes glucose from carbon dioxide & water

Catabolic pathways break down complex molecules into simpler compounds.

Catabolic pathways are spontaneous ( G < 0) and release energy: exergonic. Exergonic Reactions

Anabolic pathways build complicated molecules from simpler ones and consume energy.

Anabolic pathways are nonspontaneous ( G > 0) and consume energy: endergonic. Endergonic Reactions

Catabolic & Anabolic Reactions Cats – break things Anna – builds things Cells need both types of reactions; both require enzymes

The ATP Cycle *High energy compound used to drive metabolic reactions *Constantly being generated from adenosine diphosphate (ADP)

Adenine and ribose (together = adenosine), and The ATP Cycle ATP Composed of: Adenine and ribose (together = adenosine), and 3 phosphate groups

The ATP Cycle Coupled reactions Energy released by an exergonic reaction captured in ATP That ATP used to drive an endergonic reaction

Coupled Reactions Figure 6.4

Work-Related Functions of ATP ATP - needed to perform cellular work Chemical Work - Energy needed to synthesize macromolecules Transport Work - Energy needed to pump substances across plasma membrane Mechanical Work - Energy needed to contract muscles, beat flagella, etc

See Biochemical Pathway Animation Enzymes See Biochemical Pathway Animation Enzymes Protein molecules that function as catalysts The reactants of an enzymatically accelerated reaction are called substrates

Enzymes: Energy of Activation Reactants often “reluctant” to participate in reaction Energy must be added to at least one reactant to initiate the reaction Energy of activation Enzyme Operation: Enzymes operate by lowering the energy of activation Accomplished by bringing the substrates into contact with one another

Energy of Activation Energy of activation (Ea) is energy that must be added to cause molecules to react.

Lower Ea

Energy of Activation

Enzyme-Substrate Complex Induced fit model The active site complexes with the substrates Causes active site to change shape Shape change forces substrates together or apart… initiating or breaking bonds Enzymes Animation

Induced Fit Model

Synthesis Reaction

Degradation or Decomposition reaction

Factors Affecting Enzyme Activity Substrate concentration Enzyme activity increases with substrate concentration More collisions between substrate molecules and the enzyme Temperature Enzyme activity increases with temperature Warmer temperatures cause more effective collisions between enzyme and substrate However, hot temperatures destroy enzyme pH Most enzymes are optimized for a particular pH

Factors Affecting Enzyme Activity: Temperature

Denaturation is when a protein unravels and loses its normal structure and function Generally irreversible Denaturation Figure 5.23 Denaturation and renaturation of a protein Normal protein Denatured protein

Factors Affecting Enzyme Activity: pH

Factors Affecting Enzyme Activity Cells can affect presence/absence of enzyme Cells can affect concentration of enzyme Cells can activate or deactivate enzyme Enzyme Cofactors - Non-protein molecules that assist enzymes. (often metal ions, Fe2+) Coenzymes are organic cofactors, like some vitamins Phosphorylation – some require addition of a phosphate

Enzyme Cofactors (& Coenzymes) This enzyme is DNA polymerase. It makes copies of DNA. The purple things are magnesium (Mg), a mineral. Mg is a cofactor for DNA polymerase. This is why you need some Mg in your diet. Groove Groove Some enzymes need cofactors to work; these are non-protein groups that attach to the enzyme. Ex. Minerals such as zinc or Mg Many vitamins (because they are organic are important because they are called coenzymes

Factors Affecting Enzyme Activity: Activation by Phosphorylation

Factors Affecting Enzyme Activity Reversible enzyme inhibition When a substance known as an inhibitor binds to an enzyme and decreases its activity Competitive inhibition – substrate and the inhibitor are both able to bind to active site Noncompetitive inhibition – the inhibitor binds not at the active site, but at the allosteric site Feedback inhibition – The end product of a pathway inhibits the pathway’s first enzyme

Competitive Inhibition In competitive inhibition, another molecule is similar to enzymes substrate, competes with true substrate for enzyme’s active site, resulting in decreased product formation.

Noncompetitive Inhibition In noncompetitive inhibition, a molecule binds to allosteric site, a site other than active site, hereby changing the three-dimensional structure of enzyme and ability to bind to its substrate.

Allosteric Enzymes Allosteric Enzymes- 2 binding sites Active Site – substrate binds to Allosteric Site – allosteric affector binds Allosteric Activator – molecule binds to allosteric site and ACTIVATES enzyme. Creates active form of enzyme. Allosteric Inhibitor - molecule binds to allosteric site and INHIBITS enzyme. Creates inactive form of enzyme.

Factors Affecting Enzyme Activity: Feedback Inhibition See Feedback Inhibition Animation

See Biochemical Pathway Animation Enzymes See Biochemical Pathway Animation Each reaction in a metabolic pathway requires a unique and specific enzyme End product will not appear unless ALL enzymes present and functional E1 E2 E3 E4 E5 E6 A  B  C  D  E  F  G

“A” is Initial Reactant Metabolic Pathways Reactions are usually occur in a sequence Such linked reactions form a metabolic pathway Begins with a particular reactant, Proceeds through several intermediates, and Terminates with a particular end product AB C D E FG “G” is End Product “A” is Initial Reactant Intermediates

amanitin (mushroom toxin) Enzyme Inhibitors amanitin (mushroom toxin) This enzyme is RNA polymerase. It reads the information in the genetic code in DNA. Groove active site Inhibition is when the wrong molecule (an inhibitor) binds, blocking the active site; substrate can’t bind Many poisons are inhibitors of essential enzymes (e.g. death cap mushroom, arsenic, cadmium)

Irreversible Inhibition Materials that irreversibly inhibit an enzyme are known as poisons Cyanides inhibit enzymes resulting in all ATP production Penicillin inhibits an enzyme unique to certain bacteria Heavy metals irreversibly bind with many enzymes Nerve gas irreversibly inhibits enzymes required by nervous system