6.1 Cells and the Flow of Energy Energy is the ability to do work or bring about change. Forms of Energy –Kinetic energy is the energy of motion. –Potential energy is stored energy.

Flow of Energy

6.1 Cells and the Flow of Energy Two Laws of Thermodynamics –Energy cannot be created or destroyed, but it can be changed from one form to another. –Energy cannot be changed from one form to another without a loss of usable energy.

6.1 Cells and the Flow of Energy

Cells and Entropy –Entropy refers to the relative amount of disorganization. –Energy transformations in cells increase the amount of entropy.

6.1 Cells and the Flow of Energy Processes in living organisms require an input of energy that is ultimately lost as heat.

6.2 Metabolic Reactions and Energy Transformations Metabolism is the sum of all the chemical reactions that occur in a cell.

6.2 Metabolic Reactions and Energy Transformations Metabolism is the sum of all the chemical reactions that occur in a cell. A + B C + D (reactants) (products)

6.2 Metabolic Reactions and Energy Transformations Free energy (∆G) is the amount of energy available.

6.2 Metabolic Reactions and Energy Transformations Free energy (∆G) is the amount of energy available. –Exergonic reactions are ones where energy is released (∆G is negative)

6.2 Metabolic Reactions and Energy Transformations Free energy (∆G) is the amount of energy available. –Exergonic reactions are ones where energy is released (∆G is negative) –Endergonic reactions require an input of energy. (∆G is positive)

6.2 Metabolic Reactions and Energy Transformations ATP: Energy for Cells –ATP stands for adenosine triphosphate, the common energy currency for cells.

6.2 Metabolic Reactions and Energy Transformations ATP: Energy for Cells –ATP stands for adenosine triphosphate, the common energy currency for cells. –ATP is generated from ADP (adenosine diphosphate) + an inorganic phosphate molecule ( P )

The ATP Cycle

6.2 Metabolic Reactions and Energy Transformations Structure of ATP –ATP is a nucleotide that is composed of: Adenine (a nitrogen-containing base) Ribose (a 5-carbon sugar) Three phosphate groups

6.2 Metabolic Reactions and Energy Transformations Structure of ATP –ATP is a “high energy” compound because a phosphate group can easily be removed.

6.2 Metabolic Reactions and Energy Transformations Coupled Reactions –The energy released by an exergonic reaction is used to drive an endergonic reaction.

Coupled Reactions

6.3 Metabolic Pathways and Enzymes Metabolic pathways are a series of linked reactions. –These begin with a specific reactant and produce an end product

6.3 Metabolic Pathways and Enzymes Enzymes are usually proteins that function to speed a chemical reaction. –Enzymes serve as catalysts

A Metabolic Pathway

6.3 Metabolic Pathways and Enzymes The Energy of Activation (E a ) is the energy that must be added to cause molecules to react with one another.

Energy of Activation

6.3 Metabolic Pathways and Enzymes How Enzymes Function –Enzyme binds substrate to form a complex –E + S  ES  E + P

Enzymatic Action

6.3 Metabolic Pathways and Enzymes How Enzymes Function –Enzyme binds substrate to form a complex –E + S  ES  E + P –Induced fit model Substrate and active site shapes don’t match exactly Active site is induced to undergo a slight change in shape to accommodate substrate binding

Induced Fit Model

6.3 Metabolic Pathways and Enzymes Factors Affecting Enzymatic Speed –Substrate Concentration –Temperature and pH –Enzyme Activation –Enzyme Inhibition –Enzyme Cofactors

6.3 Metabolic Pathways and Enzymes Substrate Concentration Enzyme activity increases as substrate concentration increases because there are more collisions between substrate and enzyme Maximum rate is achieved when all active sites of an enzyme are filled continuously with substrate

Metabolic Pathways and Enzymes Temperature –Enzyme activity increase as temperature rises –Higher temperatures cause more effective collisions between enzymes and substrates –High temperatures may denature an enzyme, inhibiting its ability to bind to substrates

The Effect of Temperature on the Rate of Reaction

Metabolic Pathways and Enzymes pH Each enzyme has an optimal pH Enzyme structure is pH dependent Extremes of pH can denature an enzyme by altering its structure

Effect of pH on the Rate of Reaction

Metabolic Pathways and Enzymes Enzyme Activation –Cell regulates metabolism by regulating which enzymes are active –Genes producing enzymes can be turned on or off to regulate enzyme concentration –In some cases a signaling molecule is used to activate an enzyme

Metabolic Pathways and Enzymes Enzyme Inhibition –Occurs when enzyme cannot bind its substrate –Activity of cell enzymes is regulated by feedback inhibition –Ex: when product is abundant it binds to the enzyme’s active site and blocks further production –When product is used up, it is removed from the active site –In a more complex type of inhibition, product binds to a site other than the active site, which changes the shape of the active site –Poisons are often enzyme inhibitors

Feedback Inhibition

Metabolic Pathways and Enzymes Enzyme Cofactors –Molecules which help enzyme function –Copper and zinc are examples of inorganic cofactors –Organic non-protein cofactors are called coenzymes Vitamins are often components of coenzymes

6.4 Oxidation-Reduction and the Flow of Energy Oxidation-Reduction –Oxidation is the loss of electrons –Reduction is the gaining of electrons –Ex: when oxygen combines with a metal like Mg, oxygen receives electrons (becomes negatively charged) and Mg loses electrons (becomes positively charged) We say Mg has become oxidized, and oxygen is reduced (has a negative charge) when MgO forms

6.4 Oxidation-Reduction and the Flow of Energy Oxidation-Reduction –The term oxidation is used even when oxygen is not involved Ex: Na + + Cl -  NaCl in which sodium is oxidized and chloride is reduced –This also applies to covalent reactions involving hydrogen atoms –Oxidation is the loss of hydrogen and reduction is the gain of hydrogen atoms

6.4 Oxidation-Reduction and the Flow of Energy. Photosynthesis –energy + 6CO 2 +6H 2 O  C 6 H 12 O 6 + 6O 2 –Hydrogen atoms are transferred from water to carbon dioxide and glucose is formed –Energy is required and this comes in the form of light energy from the sun –Chloroplasts convert solar energy to ATP which is then used along with hydrogen to reduce carbon dioxide to glucose

Oxidation-reduction and the flow of energy cont’d. Cell Respiration –C 6 H 12 O 6 + 6O 2  6CO 2 + 6H 2 O + energy –Glucose is oxidized (lost hydrogen atoms) –Oxygen is reduced to form water –Complete oxidation of a mole of glucose produces 686 kcal of energy –This energy is used to form ATP –The oxidation of glucose to form ATP is done is a series of small steps to increase efficiency

6.4 Oxidation-Reduction and the Flow of Energy. Organelles and the flow of energy –Cycling of molecules between chloroplasts and mitochondria allows energy to flow from sun to all living things –Chloroplasts use light energy from the sun to make carbohydrates –Mitochondria break down carbohydrates to form ATP –Cell respiration produces carbon dioxide and water which are used in photosynthesis

Relationship of Chloroplasts to Mitochondria