Chapter 8 Warm-Up Define the term “metabolism”. List 3 forms of energy. Where does the energy available for nearly all living things on earth come from?

Ch. 8 Warm-Up What are the 1st and 2nd laws of thermodynamics? Give the definition and an example of: Catabolic reaction Anabolic reaction Is the breakdown of glucose in cellular respiration exergonic or endergonic?

Ch. 8 Warm-Up Draw and label the following: enzyme, active site, substrate. Describe what is meant by the term induced fit. What types of factors can affect an enzyme’s function?

An Introduction to Metabolism Chapter 8 An Introduction to Metabolism

What You Need To Know: Examples of endergonic and exergonic reactions. The key role of ATP in energy coupling. That enzymes work by lowering the energy of activation. The catalytic cycle of an enzyme that results in the production of a final product. The factors that influence enzyme activity.

The living cell Bioluminescence Is a miniature factory where thousands of reactions occur Converts energy in many ways Figure 8.1 Bioluminescence

Metabolism Is the totality of an organism’s chemical reactions Arises from interactions between molecules An organism’s metabolism transforms matter and energy, subject to the laws of thermodynamics

Metabolism is the totality of an organism’s chemical reactions Manage the materials and energy resources of a cell

Catabolic pathways release energy by breaking down complex molecules into simpler compounds Eg. digestive enzymes break down food  release energy Anabolic pathways consume energy to build complex molecules from simpler ones Eg. amino acids link to form muscle protein

Energy = capacity to do work Kinetic energy (KE): energy associated with motion Heat (thermal energy) is KE associated with random movement of atoms or molecules Potential energy (PE): stored energy as a result of its position or structure Chemical energy is PE available for release in a chemical reaction Energy can be converted from one form to another Eg. chemical  mechanical  electrical

Organisms are open systems Thermodynamics is the study of energy transformations that occur in nature A closed system, such as liquid in a thermos, is isolated from its surroundings In an open system, energy and matter can be transferred between the system and its surroundings Organisms are open systems

The First Law of Thermodynamics The energy of the universe is constant Energy can be transferred and transformed Energy cannot be created or destroyed Also called the principle of Conservation of Energy

An example of energy conversion Figure 8.3  First law of thermodynamics: Energy can be transferred or transformed but Neither created nor destroyed. For example, the chemical (potential) energy in food will be converted to the kinetic energy of the cheetah’s movement in (b). (a) Chemical energy

The Second Law of Thermodynamics Every energy transfer or transformation increases the entropy (disorder) of the universe During every energy transfer or transformation, some energy is unusable, often lost as heat

The Second Law of Thermodynamics According to the second law of thermodynamics Spontaneous changes that do not require outside energy increase the entropy, or disorder, of the universe The Second Law of Thermodynamics Figure 8.3  Second law of thermodynamics: Every energy transfer or transformation increases the disorder (entropy) of the universe. For example, disorder is added to the cheetah’s surroundings in the form of heat and the small molecules that are the by-products of metabolism. (b) Heat co2 H2O +

Living systems Increase the entropy of the universe Use energy to maintain order

A metabolic pathway has many steps Metabolic Pathways A metabolic pathway has many steps That begin with a specific molecule and end with a product That are each catalyzed by a specific enzyme Enzyme 1 Enzyme 2 Enzyme 3 A B C D Reaction 1 Reaction 2 Reaction 3 Starting molecule Product

Types of Metabolic Pathways Catabolic pathways Break down complex molecules into simpler compounds Release energy Anabolic pathways Build complicated molecules from simpler ones Consume energy

Energy can be converted from one form to another On the platform, a diver has more potential energy. Diving converts potential energy to kinetic energy. Climbing up converts kinetic energy of muscle movement to potential energy. In the water, a diver has less potential energy. Figure 8.2

Free Energy Free energy measures the portion of a system’s energy that can perform work when the temperature & pressure are uniform throughout the system. (like in cells) The free-energy change of a reaction tells us whether the reaction occurs spontaneously A living system’s free energy Is energy that can do work under cellular conditions

Change in free energy, ∆G The change in free energy, ∆G during a biological process Is related directly to the enthalpy change (∆H) and the change in entropy ∆G = ∆H – T∆S T = Absolute temp in Kelvin (K)

∆G The value of ∆ G for a reaction at any moment in time tells us two things. The sign of ∆ G tells us in what direction the reaction has to shift to reach equilibrium. The magnitude of ∆ G tells us how far the reaction is from equilibrium at that moment.

The system is at equilibrium At maximum stability The system is at equilibrium Chemical reaction. In a cell, a sugar molecule is broken down into simpler molecules. . Diffusion. Molecules in a drop of dye diffuse until they are randomly dispersed. Gravitational motion. Objects move spontaneously from a higher altitude to a lower one. More free energy (higher G) Less stable Greater work capacity Less free energy (lower G) More stable Less work capacity In a spontaneously change The free energy of the system decreases (∆G <0) The system becomes more stable The released free energy can be harnessed to do work (a) (b) (c) Figure 8.5 

Free Energy During a spontaneous change Free energy decreases and the stability of a system increases For a spontaneous reaction to occur: Loss of enthalpy (Heat) -or- Loss of order (Gain in entropy) -or both

Free energy: part of a system’s energy available to perform work G = change in free energy Exergonic reaction: energy is released Spontaneous reaction G < 0 Endergonic reaction: energy is required Absorb free energy G > 0

Exergonic and Endergonic Reactions in Metabolism An exergonic reaction Proceeds with a net release of free energy and is spontaneous Figure 8.6 Reactants Products Energy Progress of the reaction Amount of energy released (∆G <0) Free energy (a) Exergonic reaction: energy released

(b) Endergonic reaction: energy required Is one that absorbs free energy from its surroundings and is non-spontaneous Figure 8.6 Energy Products Amount of energy released (∆G>0) Reactants Progress of the reaction Free energy (b) Endergonic reaction: energy required

Reactions in a closed system Eventually reach equilibrium Figure 8.7 A (a) A closed hydroelectric system. Water flowing downhill turns a turbine that drives a generator providing electricity to a light bulb, but only until the system reaches equilibrium. ∆G < 0 ∆G = 0

Reactions in an open system Cells in our body Experience a constant flow of materials in and out, preventing metabolic pathways from reaching equilibrium Figure 8.7 (b) An open hydroelectric system. Flowing water keeps driving the generator because intake and outflow of water keep the system from reaching equilibrium. ∆G < 0

An analogy for cellular respiration Figure 8.7 (c) A multi-step open hydroelectric system. Cellular respiration is analogous to this system: Glucose is broken down in a series of exergonic reactions that power the work of the cell. The product of each reaction becomes the reactant for the next, so no reaction reaches equilibrium. ∆G < 0

A cell does three main kinds of work: Mechanical Transport Chemical Cells manage energy resources to do work by energy coupling: using an exergonic process to drive an endergonic one

ATP (adenosine triphosphate) is the cell’s main energy source in energy coupling ATP = adenine + ribose + 3 phosphates

When the bonds between the phosphate groups are broken by hydrolysis  energy is released This release of energy comes from the chemical change to a state of lower free energy, not in the phosphate bonds themselves

Phophorylation- The transferring of phosphoryl group from a donor to the recipient molecule Phosphorylation is important in living cells since it is through this that energy-rich molecules (e.g. ATPs) are formed. For instance, a phosphoryl group (phosphate) is added to ADP, thus forming ATP, usually catalysed by phosphorylases and kinases.

ATP – Adenosine Tri-phosphate ATP powers cellular work by coupling exergonic reactions to endergonic reactions A cell does three main kinds of work Mechanical Transport Chemical

How ATP Performs Work Exergonic release of Pi is used to do the endergonic work of cell When ATP is hydrolyzed, it becomes ADP (adenosine diphosphate)

Mechanical work: ATP phosphorylates motor proteins 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

Catalyst: substance that can change the rate of a reaction without being altered in the process Enzyme = biological catalyst Speeds up metabolic reactions by lowering the activation energy (energy needed to start reaction)

Substrate Specificity of Enzymes The reactant that an enzyme acts on is called the enzyme’s substrate The enzyme binds to its substrate, forming an enzyme-substrate complex The active site is the region on the enzyme where the substrate binds

INDUCED FIT: ENZYME FITS SNUGLY AROUND SUBSTRATE -- “CLASPING HANDSHAKE”

Enzyme Action: Catabolism

Enzyme Action: Anabolism

An enzyme’s activity can be affected by: temperature pH chemicals

Cofactors Cofactors are nonprotein enzyme helpers such as minerals (eg. Zn, Fe, Cu) Coenzymes are organic cofactors (eg. vitamins) Enzyme Inhibitors Competitive inhibitor: binds to the active site of an enzyme, competes with substrate Noncompetitive inhibitor: binds to another part of an enzyme  enzyme changes shape  active site is nonfunctional

Enzyme Specificity

Competitive Inhibition

Noncompetitive Inhibition

Inhibition of Enzyme Activity

Regulation of Enzyme Activity To regulate metabolic pathways, the cell switches on/off the genes that encode specific enzymes Allosteric regulation: protein’s function at one site is affected by binding of a regulatory molecule to a separate site (allosteric site) Activator – stabilizes active site Inhibitor – stabilizes inactive form Cooperativity – one substrate triggers shape change in other active sites  increase catalytic activity

Feedback Inhibition End product of a metabolic pathway shuts down pathway by binding to the allosteric site of an enzyme Prevent wasting chemical resources, increase efficiency of cell

Feedback Inhibition