Mader: Biology 8 th Ed. Metabolism: Energy and Enzymes Chapter 6

Mader: Biology 8th Ed.

Metabolism: Energy and Enzymes

Chapter 6


Outline

• Forms of Energy• Laws of Thermodynamics• Metabolic Reactions• ATP• Metabolic Pathways• Energy of Activation• Enzymes• Photosynthesis• Cellular Respiration


Forms of Energy

• Kinetic - Energy of motion.– Mechanical

• Potential - Stored energy.– Chemical


Laws of Thermodynamics

• First law (law of conservation of energy) states: – Energy cannot be created or destroyed,

but it can be changed from one form to another.

• Second law states:– Energy cannot be changed from one form

to another without a loss of usable energy.


Cells and Entropy

• Second law can also be explained as every energy transformation makes the universe less organized and more disordered.– Entropy

Second law means that every cellular process increases the total entropy of the universe.


Cells and Entropy


Metabolic Reactions

• Metabolism - Sum of cellular chemical reactions.– Reactants and products

• Free energy is the amount of energy available to perform work.– Exergonic Reactions - Reactants have

more free energy than products.– Endergonic Reactions - Products have

more free energy than reactants.


ATP

• Adenosine triphosphate (ATP) is constantly being generated from Adenosine diphosphate (ADP).– Composed of adenine and ribose

(adenosine) and three phosphate groups.


ATP Cycle


Coupled Reactions

• In coupled reactions, the energy released by an exergonic reaction drives an endergonic reaction.


Coupled Reactions


Function of ATP

• 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.


Metabolic Pathways

• Reactions are usually part of a series of linked reactions.– Begin with a particular reactant and

terminate with an end product.• Enzymes are protein molecules that function

as organic catalysts to speed a chemical reaction.


Energy of Activation

• The energy that must be added to cause molecules to react with one another is called the energy of activation.– Enzymes lower energy of activation by

bringing the substrates into contact with one another.


Energy of Activation


Enzyme-Substrate Complex


Enzyme-Substrate Complex

• In most instances, only the active site complexes with the substrates.– Active site undergoes a change in shape

to accommodate the substrates.Induced fit model


Enzyme Speed

• Generally, enzyme activity increases as substrate concentration increases.– More collisions between substrate

molecules and the enzyme.• As temperature rises, enzyme activity

increases.– Warmer temperatures cause more

effective collisions between enzyme and substrate.


Enzyme Speed

– If temperature rises beyond a certain point, the enzyme becomes denatured and the enzyme activity levels out.

• Enzymes also have an optimal pH.


Enzyme Concentration

• Cells regulate which enzymes are present and/or active.– Enzyme Cofactors

VitaminsPhosphorylation

Enzyme Inhibition Feedback Inhibition


Feedback Inhibition


Feedback Inhibition

• Most metabolic pathways are regulated by another type of feedback inhibition.– End product of the pathway binds to an

allosteric site.Binding shuts down the pathway, and

no more product is produced.


Oxidation-Reduction

• In redox reactions, electrons pass from one molecule to another.– Oxidation is the loss of electrons.– Reduction is the gain of electrons.

• Oxidation and reduction always take place at the same time as one molecule accepts the electrons given up by another molecule.


Photosynthesis

• Carbon dioxide + water + solar energy yields glucose and oxygen.

6 CO2 + 6 H2O + energy C6H12O6 + 6 O2

• Chloroplasts capture solar energy and convert it via electron transport chain to ATP.

• Coenzyme active during photosynthesis.

NADP+ + 2e- + H+ NADPH


Cellular Respiration

• Glucose + oxygen yields carbon dioxide + water + energy.

C6H12O6 + 6 O2 6 CO2 + 6 H2O + energy

• Most oxidations involve a coenzyme:

NAD+ + 2e- + H+ NADH


Electron Transport System

• A series of membrane-bound carriers that pass electrons from one carrier to another.– High-energy electrons delivered, and low-

energy electrons leave.


ATP Production

• Chemiosmosis: Production of ATP due to a hydrogen ion gradient across a membrane.


Review• Forms of Energy• Laws of Thermodynamics• Metabolic Reactions• ATP• Metabolic Pathways• Energy of Activation• Enzymes• Photosynthesis• Cellular Respiration


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Mader: Biology 8 th Ed. Metabolism: Energy and Enzymes Chapter 6