Chapter 8 An Introduction To Metabolism

Metabolism u The totality of an organism’s chemical processes. u Concerned with managing the material and energy resources of the cell.

Catabolic Pathways u Pathways that break down complex molecules into smaller ones, releasing energy. u Example: Respiration

Anabolic Pathways u Pathways that consume energy, building complex molecules from smaller ones. u Example: Photosynthesis

Energy u Ability to do work. u The ability to rearrange a collection of matter. u Forms of energy: u Kinetic u Potential u Activation

Kinetic Energy u Energy of action or motion.

Potential Energy u Stored energy or the capacity to do work.

Activation Energy u Energy needed to convert potential energy into kinetic energy. Potential Energy Activation Energy

Energy Transformation u Governed by the Laws of Thermodynamics.

1st Law of Thermodynamics u Energy can be transferred and transformed, but it cannot be created or destroyed. u Also known as the law of “Conservation of Energy”

2nd Law of Thermodynamics u Each energy transfer or transformation increases the entropy of the universe.

Entropy u Measure of disorder.

Summary u The quantity of energy in the universe is constant, but its quality is not.

Question? u How does Life go against Entropy? u By using energy from the environment or external sources (e.g. food, light).

Free Energy u The portion of a system's energy that can perform work.

Free Energy G = H - TS G = free energy of a system H = total energy of a system T = temperature in o K S = entropy of a system

Free Energy of a System u If the system has: u more free energy u it is less stable u It has greater work capacity

Free Energy Changes

Spontaneous Process u If the system is unstable, it has a greater tendency to change spontaneously to a more stable state. u This change provides free energy for work.

Chemical Reactions u Are the source of energy for living systems. u Are based on free energy changes.

Reaction Types u Exergonic: chemical reactions with a net release of free energy. u Endergonic: chemical reactions that absorb free energy from the surroundings.

Exergonic/Endergonic

Biological Examples u Exergonic - respiration u Endergonic - photosynthesis

Cell - Types of Work u Mechanical - muscle contractions u Transport - pumping across membranes u Chemical - making polymers

Cell Energy u Couples an exergonic process to drive an endergonic one. u ATP is used to couple the reactions together.

ATP u Adenosine Triphosphate u Made of: - Adenine (nitrogenous base) - Ribose (pentose sugar) - 3 phosphate groups

Adenine Ribose Phosphates

Key to ATP u Is in the three phosphate groups. u Negative charges repel each other and makes the covalent bonds between the phosphates unstable.

ATP u Works by energizing other molecules by transferring phosphate groups.

ATP vs Food u ATP: u Renewable energy resource. u Unstable bonds u Food: u Long term energy storage u Stable bonds

ATP Cycles u Energy released from ATP drives anabolic reactions. u Energy from catabolic reactions “recharges” ATP.

ATP Cycle

ATP in Cells u A cell's ATP content is recycled every minute. u Humans use close to their body weight in ATP daily. u No ATP production equals quick death.

Enzymes u Biological catalysts made of protein. u Cause the rate of a chemical reaction to increase.

Chemical Reaction AB + CD AC + BD AB and CD are “reactants” AC and BD are “products”

Enzymes u Lower the activation energy for a chemical reaction to take place.

Enzyme Terms u Substrate - the material and enzyme works on. u Enzyme names: Ex. Sucrase - ase name of an enzyme 1st part tells what the substrate is. (Sucrose)

Enzyme Name u Some older known enzymes don't fit this naming pattern. u Examples: pepsin, trypsin

Active Site u The area of an enzyme that binds to the substrate. u Structure is designed to fit the molecular shape of the substrate. u Therefore, each enzyme is substrate specific.

Models of How Enzymes Work 1. Lock and Key model 2. Induced Fit model

Lock and Key Model u Substrate (key) fits to the active site (lock) which provides a microenvironment for the specific reaction.

Induced Fit Model u Substrate “almost” fits into the active site, causing a strain on the chemical bonds, allowing the reaction.

Substrate Active Site

Enzymes u Usually specific to one substrate. u Each chemical reaction in a cell requires its own enzyme.

Factors that Affect Enzymes u Environment u Cofactors u Coenzymes u Inhibitors u Allosteric Sites

Environment u Factors that change protein structure will affect an enzyme. u Examples: u pH shifts u temperature u salt concentrations

u Cofactors: non-organic helpers to enzymes. Ex. Fe, Zn, Cu u Coenzymes: organic helpers to enzymes. Ex. vitamins

Enzyme Inhibitors u Competitive - mimic the substrate and bind to the active site. u Noncompetitive - bind to some other part of the enzyme.

Allosteric Regulation u The control of an enzyme complex by the binding of a regulatory molecule. u Regulatory molecule may stimulate or inhibit the enzyme complex.

Allosteric Regulation

Control of Metabolism u Is necessary if life is to function. u Controlled by switching enzyme activity "off" or "on” or separating the enzymes in time or space.

Types of Control u Feedback Inhibition u Structural Order

Feedback Inhibition u When a metabolic pathway is switched off by its end- product. u End-product usually inhibits an enzyme earlier in the pathway.

Structural Order u Separation of enzymes and metabolic pathways in time or space by the cell's organization. u Example: enzymes of respiration

Summary u Recognize that Life must follow the Laws of Thermodynamics. u The role of ATP in cell energy. u How enzymes work.