Enzymes & Metabolism: Part 1 Unit 5

Metabolism is the sum of an organism’s chemical reactions Metabolism arises from interactions between molecules within the cell http://www.encognitive.com/images/metabolic-pathways.png

A metabolic pathway begins with a specific molecule and ends with a product Each step is catalyzed by a specific enzyme

ENZYMES THAT WORK TOGETHER IN A PATHWAY CAN BE Concentrated in specific location Covalently bound in complex Soluble with free floating intermediates Attached to a membrane in sequence Biochemistry Lehninger

CATABOLIC PATHWAY (CATABOLISM) Release of energy by the breakdown of complex molecules to simpler compounds EX: digestive enzymes break down food ANABOLIC PATHWAY (ANABOLISM) consumes energy to build complicated molecules from simpler ones EX: linking amino acids to form proteins E.g.: Hydrolysis E.g.: Dehydration Synthesis http://www.sciencelearn.org.nz/var/sciencelearn/storage/images/contexts/nanoscience/sci_media/images/chemical_reactions_involve_making_new_combinations/53823-2-eng-NZ/chemical_reactions_involve_making_new_combinations_full_size_landscape.jpg

Forms of Energy ENERGY = capacity to cause change Energy exists in various forms (some of which can perform work) Energy can be converted from one form to another

KINETIC ENERGY – energy associated with motion HEAT (thermal energy) is kinetic energy associated with random movement of atoms or molecules POTENTIAL ENERGY = energy that matter possesses because of its location or structure CHEMICAL energy is potential energy available for release in a chemical reaction

THERMODYNAMICS = the study of energy transformations Organisms are open systems OPEN system energy + matter can be transferred between the system and its surroundings http://ag.ansc.purdue.edu/sheep/ansc442/Semprojs/2003/spiderlamb/eatsheep.gif

The First Law of Thermodynamics = energy of the universe is constant Energy cannot be created or destroyed CONSERVATION OF ENERGY http://www.pxleyes.com/photoshop-picture/4a3b747566555/remote-control.html http://www.suncowboy.com/solar101.php

The Second Law of Thermodynamics During every energy transfer or transformation entropy (disorder) of the universe INCREASES some energy is unusable, often lost as heat (endotherms) http://hyperphysics.phy-astr.gsu.edu/hbase/therm/entrop.html http://www.janebluestein.com/articles/whatswrong.html

ORGANISMS are energy TRANSFORMERS! Second law of thermodynamics First law of thermodynamics Chemical energy Heat CO2 H2O ORGANISMS are energy TRANSFORMERS! Spontaneous processes occur without energy input; they can happen quickly or slowly For a process to occur without energy input, it must increase the entropy of the universe

Free-Energy Change (G) can help tell which reactions will happen ∆G = change in free energy ∆H = change in total energy (enthalpy) or change in heat ∆S = entropy (disorder) T = temperature ∆G = ∆H - T∆S Only processes with a negative ∆G are spontaneous Spontaneous processes can be harnessed to perform work

Exergonic and Endergonic Reactions in Metabolism EXERGONIC reactions (- ∆G) Release energy are spontaneous ENDERGONIC reactions (+ ∆G) Absorb energy from their surroundings are non-spontaneous

A cell does three main kinds of work: ATP powers cellular work by coupling exergonic reactions to endergonic reactions A cell does three main kinds of work: Mechanical (cilia, muscle contractions) Transport (movement of molecules) Chemical (making polymers) In the cell, the energy from the exergonic reaction of ATP hydrolysis can be used to drive an endergonic reaction Overall, the coupled reactions are exergonic

Reactants: Glutamic acid LE 8-11 P i P Motor protein Protein moved Mechanical work: ATP phosphorylates motor proteins Membrane protein ADP ATP + P i P P i Solute Solute transported Transport work: ATP phosphorylates transport proteins P NH2 + NH3 Glu + P i Glu Reactants: Glutamic acid and ammonia Product (glutamine) made Chemical work: ATP phosphorylates key reactants

Energy to charge ATP comes from catabolic reactions ATP (adenosine triphosphate) is the cell’s renewable and reusable energy shuttle Energy to charge ATP comes from catabolic reactions Adenine Phosphate groups Ribose

Energy for cellular work provided by the loss of phosphate from ATP Energy from catabolism (used to charge up ADP into ATP ADP + P i

hydrolysis Endergonic reaction: DG is positive, reaction is not spontaneous NH2 + NH3 DG = +3.4 kcal/mol Glu Glu Glutamic acid Ammonia Glutamine Exergonic reaction: DG is negative, reaction is spontaneous ATP + H2O ADP P + DG = –7.3 kcal/mol i hydrolysis Coupled reactions: Overall DG is negative; Together, reactions are spontaneous DG = –3.9 kcal/mol

Every chemical reaction between molecules involves bond breaking and bond forming ACTIVATION ENERGY = amount of energy required to get chemical reaction started Activation energy is often supplied in the form of heat from the surroundings IT’S LIKE PUSHING A SNOWBALL UP A HILL . . . Once you get it up there, it can roll down by itself http://www.chuckwagondiner.com/art/matches.jpg http://plato.acadiau.ca/COURSES/comm/g5/Fire_Animation.gif

The Activation Energy Barrier LE 8-14 The Activation Energy Barrier A B C D Transition state A B EA Free energy C D Reactants A B DG < O C D Products Progress of the reaction

CATALYST = a chemical agent that speeds up a reaction without being consumed by the reaction ENZYMES = biological catalysts Most enzymes are PROTEINS Exception = ribozymes (RNA)

ENZYMES work by LOWERING ACTIVATION ENERGY; Course of reaction without enzyme EA without enzyme EA with enzyme is lower Reactants Free energy Course of reaction with enzyme DG is unaffected by enzyme Products Progress of the reaction ENZYMES work by LOWERING ACTIVATION ENERGY;

ENZYMES LOWER ACTIVATION ENERGY BY Orienting substrates correctly Straining substrate bonds Providing a favorable microenvironment Enzymes change ACTIVATION ENERGY but NOT energy of REACTANTS or PRODUCTS http://sarahssureshots.wikispaces.com/Focus+on+Proteins http://www.ac-montpellier.fr/sections/personnelsen/ressources-pedagogiques/education-artistique/consultation-avis-du

ENZYMES Most are proteins Lower activation energy Specific Shape determines function Reusuable Unchanged by reaction Image from: http://www.hillstrath.on.ca/moffatt/bio3a/digestive/enzanim.htm

The REACTANT that an enzyme acts on = SUBSTRATE Enzyme + substrate = ENZYME-SUBSTRATE COMPLEX Region on the enzyme where the substrate binds = ACTIVE SITE Substrate held in active site by WEAK interactions (ie. hydrogen and ionic bonds)

LOCK & KEY Active site on enzyme fits substrate exactly TWO MODELS PROPOSED LOCK & KEY Active site on enzyme fits substrate exactly INDUCED FIT Binding of substrate causes change in active site so it fits substrate more closely http://www.grand-illusions.com/images/articles/toyshop/trick_lock/mainimage.jpg http://commons.wikimedia.org/wiki/File:Induced_fit_diagram.png