Chapter 8: Intro to Metabolism

Energy: Defined: The capacity to do work

Energy 1.Potential 2.Kinetic 3.Thermal 4.Chemical

Thermodynamics Study of E transformations that occur in a collection of matter System: matter under study Surroundings: rest of the universe Closed vs. Open systems

1 st Law of Thermodynamics Law of Conservation of Energy E in the universe is constant E changes form not created not destroyed

2 nd Law of Thermodynamics Entropy- measure of disorder or randomness

2 nd Law of Thermodynamics Every E transfer or transformation increases the entropy of the universe Order can be increased locally, but Entropy in the universe is unstoppable (snowball effect)

Recycling E Why can ’ t organisms recycle their E? During transformations, some E becomes unusable energy (heat) Most E from food is lost as heat Heat is only a useable form of E if there is a temperature difference in a system

What happens to the Heat The unusable energy creates disorder in the universe More structured molecules have less entropy, as they are broken down, they are less ordered.

Spontaneity For a process or chemical reaction to occur spontaneously, it must increase the entropy of the universe

Living Systems Increase the entropy of the universe Organisms takes in matter and energy from the surroundings and replaces them with less ordered forms E: enters the ecosystem as light leaves as heat

Metabolism Sum of all the chemical reactions inside an organism Interactions between molecules in an orderly cellular environment

Metabolic Pathway Start with a specific molecule that is altered in a series of defined steps Each chemical reaction in the pathway is catalyzed by a specific enzyme- example: urease (30,000 molecules/sec) These enzymes have the ability to be turned off and on

Two types of metabolic pathways: Catabolic Pathways Breakdown pathways “Downhill” Anabolic pathways Biosynthetic pathway Uphill pathway

Anabolic vs. Catabolic Which pathway is spontaneous? Which pathway requires energy? Where does the energy come from? Which pathway increases entropy?

Examples of anabolic and catabolic pathways: Protein synthesis Metabolism of glucose (glycolysis)

Energy flow and metabolism: Energy released from downhill, catabolic pathways can be stored and used for uphill anabolic pathways.

Gibb ’ s Free E of a System (G) Measures the portion of a system ’ s E that can perform work when temp and pressure are uniform throughout the system

ΔG = ΔH – TΔS *Can tell us if a process occurs spontaneously *- ΔG = spontaneous reaction

Free energy and spontaneity: ΔG = G final state – G initial state

Spontaneity cont. For a process to occur spontaneously, 1. enthalpy must decrease 2. temperature and entropy must increase 3. both of these processes must occur

Free Energy and Stability: During a spontaneous reaction, the reactants are more unstable than the products, the reactants have a higher G Unstable systems = high G Tendency is towards stability

Examples: Dye in water Glucose These systems will move towards stability unless something prevents it.

Equilibrium and Free Energy: When a system is in equilibrium, G is at its lowest possible value Systems never spontaneously move away from equilibrium

ΔG and Metabolism Exergonic Reaction: net release of free energy: occurs spontaneously. ΔG is negative- value represents the amount of energy available Cellular respiration

ΔG and Metabolism Endergonic: absorbs free energy from its surroundings. ΔG is positive – value represents the amount of energy required to drive the reaction ΔG is positive – value represents the amount of energy required to drive the reaction Absorbs free energy Non spontaneous

Exergonic vs. Endergonic Exergonic = downhill Endergonic = uphill

Preventing Equilibrium If a cell reaches a metabolic equilibrium it would die. There would be no free energy to do work. The constant flow of materials in and out of cells keeps the metabolic pathways from reaching equilibrium (open system)

The coupling of reactions: The cell performs three types of work: what are they?

Cell Work: 1. Mechanical Work: 2. Transport Work: 3. Chemical Work:

What’s ATP: Adenosine Triphosphate Composed of: 1. Adenine 2 Ribose 3. 3 PO 4 3-

The Structure of ATP

ATP Converting ATP to ADP + P i hydrolysis releases approx. 7.3 kcal/mol High amount of energy in relation to what other molecules can deliver Is this exergonic or endergonic?

ATP Tri- phosphate region of ATP is very unstable: Must lose its terminal phosphate to become more stable Releasing energy Chemical change to a state of lower free energy

How ATP works Energy coupling: ATP hydrolysis (exergonic) is coupled with some endergonic process Requires the transfer of the terminal phosphate group The recipient then becomes phosphorylated Requires enzymes

The phosphorylated intermediate is much more reactive than its original form.

1. Mechanical: ATP phosphorylates the movement of motor proteins 2. Transport: ATP phosphorylates the transport of sodium and potassium against their concentration gradients 3. Chemical: ATP phosphorylates key reactants into a desired product Example: the amino acid glutamine is synthesized from glutamic acid and ammonia Back to cell work:

ATP Regeneration Free E to create ATP comes from catabolic(exergonic) reactions. Phosphorylation of ADP

ATP Cycle: Energy coupling The shuttling of inorganic phosphate and energy Coupling of exergonic and endergonic processes 10 million ATP molecules are consumed and regenerated per second per cell.

How much energy is required to make ATP? ΔG = +7.3 kcal/mol Spontaneous or non-spontaneous?

Chemical Reactions Spontaneous reactions do require some source of energy????? Usually in the form of a catalyst Enzymes Regulates the rate of metabolic reactions Slows down or stops spontaneous reactions

Chemical Reaction Logistics Involves bond breaking and bond formation See metabolism of sucrose Involves contorting one of the molecules into an unstable state Requires the absorption of energy

Activation Energy (E A ) Energy required to start a chemical reaction E needed by the molecule to contort into its unstable shape Uphill process = increase in free energy

Exergonic Reaction Transition State

Enzymes and E A Heat is usually provided to reach transition state Heat would break down complex structures like proteins, DNA, etc. Heat is also not selective enough for biological processes Enzymes hasten chemical reaction by lowering the E A

Enzyme Terminology Substrate Active Site Induced Fit

Enzymes Substrate is held in active site by weak bonds R groups in active site catalyze the conversion of the substrate Most metabolic reactions are reversible An enzyme will always catalyze in the direction of equilibrium

4 Mechanisms of Enzyme Function 1.Active site is template: orientation 2.Stretch the substrate molecules: distortion into transition state 3.Microenvironment 4.Direct participation: brief covalent bond

pH and Temperature Higher temperature help increase the rate of reaction, but at a certain point higher temps may denature the enzyme Thermophilic bacterial enzymes Every enzyme also has an optimal pH

Cofactors Nonprotein “ helper ” for catalytic activity Bound tightly or loosely to enzyme Inorganic: zinc, iron, and copper Organic (coenzyme): vitamins

Enzyme Inhibition Competitive: directly block binding of substrate to active site by mimicking shape of the substrate Noncompetitive: do not attach to active site binding of this molecule alters the shape of the enzyme including the active site binding of this molecule alters the shape of the enzyme including the active sitePenicillin

Allosteric Regulation Regulation of an enzymes active site Regulatory molecule binds to allosteric site Inhibits or stimulates enzyme activity Allosteric site: where subunits join

Allosteric Regulation Most of these enzymes have multiple polypeptide chains each having an active site Involves conformational change in one subunit which is transmitted to all other subunits

Cooperativity Active site bonding of 1 of the subunits locks all other active sites in the enzyme into active conformation

Feedback Inhibition A Metabolic pathway is switched off by the inhibitory binding of the end product to an enzyme that acts earlier in the pathway Dependent on concentration of products