INTRODUCTION TO METABOLISM.

Chapter 8 Metabolism, Energy, and Life

Objectives

• Explain the role of catabolic and anabolic pathways in cell metabolism • Distinguish between kinetic and potential energy • Distinguish between open and closed systems • Explain the first and second Laws of Thermodynamics • Distinguish between entropy and enthalpy • Understand the Gibbs equation for free energy change • Understand how “usable” energy changes with changes in enthalpy, entropy, and temperature • Understand the usefulness of free energy

How to Read a Chemical Equation

• A chemical reaction starts with reactants and finishes with products:

C 6 H 12 0 6 + 6O 2



6CO 2 +6H 2 0 + ENERGY 6CO 2 reactant +6H 2 0 + light product

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C 6 H 12 0 6 + 6O 2

• Disturbing either the concentration or the energy of the system alters the chemical equilibrium. Living things NEVER let their reactions go to equilibrium

Metabolism

• The sum of all the chemical processes occurring in an organism at one time • Concerned with the management of material and energy resources within the cell • Catabolic pathways • Anabolic pathways

Catabolic Pathways

• Pathways that release energy by breaking down complex molecules into simpler compounds • Cellular respiration • C 6 H 12 0 6 + 6O 2  6CO 2 +6H 2 0 + ENERGY

Anabolic Pathways

• Pathways that consume energy to build larger, complicated molecules from simpler ones • Polymerization • Photosynthesis 6CO 2 +6H 2 0 + light  C 6 H 12 0 6 + 6O 2

Bioenergetics

• • Study of how organisms manage their

energy

resources

Energy

matter is the capacity to do work, to move – Kinetic energy: energy that is in motion – Potential energy: stored energy based on location or structure • The rearrangement of atoms in molecules may result in the potential energy of the molecule being converted into kinetic energy

•

Kinetic energy

: energy of motion; all atoms exhibit kinetic energy as all molecules are in motion http://galileo.phys.virginia.edu/classes/109N/more_stuff/Applets/brownian/brownian.html

•

Potential energy

: amount of energy stored as a result of position or location

Energy Laws Laws of Thermodynamics

• • • The terms open or closed systems refer to whether or not energy can be transferred between the system and its surroundings (can energy be imported or exported)

First Law of Thermodynamics

: Energy can neither be created nor destroyed, only transformed from one type to another

Second Law of Thermodynamics

: Each energy transformation results in less usable (ordered) energy

Free Energy G=H-TS

Free energy (G) is the portion of system energy that can do work under uniform temperature •

Enthalpy

or work total energy is a measure of all the energy in a system • Symbolically represented as “H” •

Entropy

is a measure of randomness (disorder) • Symbolically represented as “S” Temperature (T) is measured in K



G

• The higher the G the more unstable the system • A change in free energy can occur with metabolism – Exergonic: reactions that lose energy;  G – Endergonic: reactions that gain energy; +  G – Metabolic reactions are often coupled where an exergonic reaction fuels an endergonic reaction • When  G = 0 no work can be done • When reactions go to equilibrium,  G = 0 (therefore metabolic reactions do not usually reach an equilibrium) • Energy needed for Mechanical, Chemical, and Transport workings of the cell

Objectives

• Explain the role of ATP in the cell • Describe ATP’s composition and how it performs cellular work • Explain the importance of chemical disequilibrium • Understand the energy profile of a reaction including: activation energy, free energy change, & transition state • Describe the role and mechanisms of enzymes • Explain how enzyme activity can be controlled by environmental factors, cofactors, enzyme inhibitors, and allosteric regulators • Distinguish between allosteric activation and cooperativity • Explain how metabolic pathways are regulated

ATP

• Energy molecule used to couple exergonic reactions to endergonic • Nucleotide with three phosphate groups attached to the ribose sugar • ATP has a high  G

ATP

• Energy is released from ATP through the loss of phosphate groups • Catabolic reaction resulting from hydrolysis producing ADP + P i (inorganic Phosphate) + energy (  G = -7.3Kcal/mol in the lab, -13Kcal/mol in the cell)

How ATP works

• Hydrolysis of ATP produces inorganic phosphate that is attached to a molecule involved in an endergonic process • Phosphorylation is the process of ATP transferring phosphate to a molecule • Results in a phosphorylated intermediate that can complete the intended reaction

Regeneration of ATP

• ATP loses energy when it phosphorylates an intermediate molecule of an endergonic reaction. ATP becomes ADP • Regeneration of ATP occurs when inorganic phosphate (P i ) is bound to ADP utilizing energy supplied by a catabolic reaction

How Do We Maximize Cellular Efficiency?

• Use of ATP – ATP is a good energy source because: • It can participate in a many different kinds of reactions within the cell • Usually is directly involved in reactions • Little wasted energy during phosphorylation of an intermediate • Use of enzymes – Decrease randomness of reactions • Regulation of enzymes and, thus, reactions

Enzymes

• Proteins that assist in chemical reactions may be enzymes – Specific because of conformational shape • Enzymes are catalysts –

Catalyst

: chemical that changes the rate of a reaction without being consumed – Recycled (used multiple times) • Enzymes reduce the activation energy of a reaction – Amount of energy that must be added to get a reaction to proceed

Activation Energy

• E A = Activation energy • E A is usually supplied by heat • Reactants absorb heat increasing  G making the reactants unstable so they react

How Enzymes Work

• Enzymes are substrate specific –

Substrate

: any molecule to which an enzyme will bind • Although an enzyme can be a large protein, only a specific region of the enzyme interacts with the substrate –

Active Site

: region of enzyme that “reacts” to substrate • As enzyme and substrate bind, the enzyme shape is modified to better fit the substrate – Induced fit occurs as a result of the enzyme substrate complex

Enzyme Activity

• The rate of an enzyme catalyzed reaction is influenced by 1) concentration of the substrate or 2) enzyme concentration • Some enzymes utilize 3) inorganic or 4) organic molecules as helpers – Cofactor: inorganic molecule (mineral) – Coenzyme: organic non protein molecule (vitamin)

Enzyme activity

• The rate at which an enzyme can function is dependant on several physical factors including: – 5) Temperature – 6) pH • Why?

Enzyme Regulation

• Enzyme activity may be reduced by molecules attaching to the enzyme.

• Inhibition may occur at two different locations –

competitive inhibition

: inhibitor mimics molecule that attaches to active site –

noncompetitive inhibition at an allosteric site

: inhibitor binds to enzyme away from the active site resulting in modification of active site

Control of Metabolism

• • •

Allosteric Regulation

: enzyme function may be stimulated or inhibited by attachment of molecules to an

allosteric site Feedback Inhibition

: end product of metabolic pathway may serve as allosteric inhibitor

Cooperativity

: single substrate molecule primes multiple active sites increasing activity