SoS, Dept. of Biology, Lautoka Campus BIO508 Cell Biology Slide Design: Copyright © McGraw-Hill Global Education Holdings, LLC. Lecturer: Dr.Ramesh Subramani Topic 5: Metabolism

The Energy of Life The living cell is a miniature chemical factory where thousands of reactions occur. The cell extracts energy and applies energy to perform work. Some organisms even convert energy to light, as in bioluminescence.

Metabolism An organism’s metabolism transforms matter and energy, subject to the laws of thermodynamics. Metabolism is the totality of an organism’s chemical reactions. Metabolism is an emergent property of life that arises from interactions between molecules within the cell. A metabolic pathway begins with a specific molecule and ends with a product Each step is catalyzed by a specific enzyme Enzyme 1 Enzyme 2 Enzyme 3 A B C D Reaction 1 Reaction 2 Reaction 3 Starting molecule Product

Metabolic Pathways A sequence of chemical reactions, where the product of one reaction serves as a substrate for the next, is called a metabolic pathway or biochemical pathway. Most metabolic pathways take place in specific regions of the cell. Two types of metabolic pathway occur in a cell, Catabolic pathway and Anabolic pathway.

Metabolic Pathways Catabolic pathways release energy by breaking down complex molecules into simpler compounds Cellular respiration, the breakdown of glucose in the presence of oxygen, is an example of a pathway of catabolism Anabolic pathways consume energy to build complex molecules from simpler ones The synthesis of protein from amino acids is an example of anabolism Bioenergetics is the study of how organisms manage their energy resources

Energy Energy is the capacity to cause change. Energy exists in various forms, some of which can perform work. Kinetic energy is energy associated with motion. Heat (thermal energy) is kinetic energy associated with random movement of atoms or molecules. Potential energy is energy that matter possesses because of its location or structure. Chemical energy is potential energy available for release in a chemical reaction. Energy can be converted from one form to another.

Transformations between potential A diver has more potential energy on the platform than in the water. Diving converts potential energy to kinetic energy. Transformations between potential and kinetic energy Climbing up converts the kinetic energy of muscle movement to potential energy. A diver has less potential energy in the water than on the platform.

The Laws of Energy Transformation Thermodynamics is the study of energy transformations A closed system, such as that approximated by 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 According to the first law of thermodynamics Energy cannot be created or destroyed Energy can be transferred and transformed

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

Biological Order and Disorder Cells create ordered structures from less ordered materials Organisms also replace ordered forms of matter and energy with less ordered forms The evolution of more complex organisms does not violate the second law of thermodynamics Entropy (disorder) may decrease in an organism, but the universe’s total entropy increases.

Biological Order and Disorder Living systems Increase the entropy of the universe Use energy to maintain order A living system’s free energy is energy that can do work under cellular conditions Organisms live at the expense of free energy 50µm

Free Energy Free energy is the portion of a system’s energy that is able to perform work when temperature and pressure is uniform throughout the system, as in a living cell. Free energy also refers to the amount of energy actually available to break and subsequently form other chemical bonds. Gibbs’ free energy (G) – in a cell, the amount of energy contained in a molecule’s chemical bonds (T&P constant). Change in free energy - ΔG Endergonic - any reaction that requires an input of energy Exergonic - any reaction that releases free energy

Exergonic reaction: energy released Exergonic reactions Reactants have more free energy than the products. Involve a net release of energy and/or an increase in entropy. Occur spontaneously (without a net input of energy). Reactants Products Energy Progress of the reaction Amount of energy released (∆G <0) Free energy Exergonic reaction: energy released

Endergonic reaction: energy required Endergonic Reactions Reactants have less free energy than the products. Involve a net input of energy and/or a decrease in entropy. Do not occur spontaneously. Energy Products Amount of energy released (∆G>0) Reactants Progress of the reaction Free energy Endergonic reaction: energy required

Endergonic Exergonic Product Energy supplied Energy must be supplied. Reactant Reactant Energy is released. Energy released Product Endergonic Exergonic Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

Equilibrium and Metabolism Reactions in a closed system eventually reach equilibrium and can then do no work Cells are not in equilibrium; they are open systems experiencing a constant flow of materials A catabolic pathway in a cell releases free energy in a series of reactions Closed and open hydroelectric systems can serve as analogies

Equilibrium and Metabolism Reactions in a closed system eventually reach equilibrium. 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

Equilibrium and Metabolism Cells in our body experience a constant flow of materials in and out, preventing metabolic pathways from reaching equilibrium. 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 – Glucose Catabolism A multistep 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

Energy Coupling Living organisms have the ability to couple exergonic and endergonic reactions: Energy released by exergonic reactions is captured and used to make ATP from ADP and Pi. ATP can be broken back down to ADP and Pi, releasing energy to power the cell’s endergonic reactions.

The Structure of ATP ATP (adenosine triphosphate) is the cell’s energy shuttle. ATP is composed of ribose (a sugar), adenine (a nitrogenous base), and three phosphate groups. O CH2 H OH N C HC NH2 Adenine Ribose Phosphate groups - CH

Hydrolysis of ATP The bonds between the phosphate groups of ATP’s tail can be broken by hydrolysis. Energy is released from ATP when the terminal phosphate bond is broken. This release of energy comes from the chemical change to a state of lower free energy, not from the phosphate bonds themselves.

Hydrolysis of ATP Energy is released from ATP when the terminal phosphate bond is broken. P Adenosine triphosphate (ATP) H2O + Energy Inorganic phosphate Adenosine diphosphate (ADP) P i

ATP Powers Cellular Work A cell does three main kinds of work Mechanical Transport Chemical Energy coupling is a key feature in the way cells manage their energy resources to do this work. ATP powers cellular work by coupling exergonic reactions to endergonic reactions.

Energy Coupling - ATP / ADP Cycle Releasing the third phosphate from ATP to make ADP generates energy (exergonic): Linking the phosphates together requires energy - so making ATP from ADP and a third phosphate requires energy (endergonic), Catabolic pathways drive the regeneration of ATP from ADP and phosphate ATP synthesis from ADP + P i requires energy ATP ADP + P i Energy for cellular work (endergonic, energy- consuming processes) Energy from catabolism (exergonic, energy yielding processes) ATP hydrolysis to ADP + P i yields energy

How ATP Performs Work ATP drives endergonic reactions by phosphorylation, transferring a phosphate group to some other molecule, such as a reactant. The recipient molecule is now phosphorylated. The three types of cellular work (mechanical, transport, and chemical) are powered by the hydrolysis of ATP.

How ATP Performs Work ATP drives endergonic reactions by phosphorylation, transferring a phosphate to other molecules - hydrolysis of ATP. (c) Chemical work: ATP phosphorylates key reactants P Membrane protein Motor protein P i Protein moved (a) Mechanical work: ATP phosphorylates motor proteins ATP (b) Transport work: ATP phosphorylates transport proteins Solute transported Glu NH3 NH2 + Reactants: Glutamic acid and ammonia Product (glutamine) made ADP

How ATP drives chemical work: Energy coupling using ATP hydrolysis

Acknowledgements… Any Questions?? The teaching material used in this lecture is taken from: JB Reece, LA Urry, ML Cain, SA Wasserman, PV Minorsky and RB Jackson. 2011. Campbell Biology (9th Edition), Publisher Pearson is gratefully acknowledged. Some information presented in this power point lecture presentation is collected from various sources including Google, Wikipedia, research articles and some book chapters from various biology books. Material and figures used in this presentation are gratefully acknowledged. This material is collected and presented only for teaching purpose. Any Questions?? Dr.Ramesh Subramani, Assistant Professor in Biology