UNIT IV – CELLULAR ENERGY Hillis- Ch 2.5, 6 Big Campbell ~ Ch 8,9,10 Baby Campbell ~ Ch 5,6,7

I. THE WORKING CELL Metabolism Totality (sum) of an organism’s chemical reactions Catabolic Pathways - Breaks down molecules; releases energy; EX: Cellular Respiration Anabolic Pathways - Pathway that synthesizes larger molecules from smaller ones; requires energy; EX: synthesis of AA, synthesis of proteins 2

I. THE WORKING CELL, cont Energy Kinetic Energy –energy associated with the relative motion of objects. EX: pool stick  cue ball  other balls Potential Energy – energy that matter possesses (stored) because of its location or structure. EX: water behind a dam Chemical Energy – Potential energy of molecules Thermodynamics First Law of Thermodynamics states that total amount of energy in universe is constant – can be transferred or transformed, but it cannot be created or destroyed Principle of the Conservation of Energy Second Law of Thermodynamics states that energy is lost to the environment as heat; that is, some energy becomes unusable EX: Bear catching fish for food Entropy – measure of disorder or randomness that is a consequence of the loss of useable energy during energy transfer.

I. THE WORKING CELL, cont Chemical Reactions are classified according to whether they require or produce energy Endergonic – Requires net input of energy. Energy is then stored in products as potential energy. Exergonic - Release energy. Energy Coupling – Often used in cellular metabolism. Energy released in exergonic rxn is used to drive endergonic rxn. 4

ATP . . . It’s energy 1 – 2 – 3 . . . In bonds of P ATP . . . Energy Energy in the bonds of P! 

II. ATP Powers 3 kinds of work: - Chemical (synthesis of polymers) - Transport (pumping substances across the membrane) - Mechanical (beating of cilia, contraction of muscle cells, chromosome movement) 6

II. ATP Adenosine Triphosphate Nucleotide that stores & provides usable energy to the cell Structure of ATP 5-C Sugar called Ribose Nitrogen base Adenine 3 Phosphate groups ATP contains potential energy, especially between 2nd and 3rd phosphate groups. P – P bond is unstable Easily broken by HYDROLYSIS 7

II. ATP, cont ATP → ADP + Pi Catabolic Pathway Exergonic Coupled with endergonic rxn – specifically, by transferring phosphate group from ATP to another molecule.

II. ATP, cont ADP + Pi → ATP Anabolic pathway Endergonic Mechanisms for “making” ATP Substrate-level Phosphorylation – enzyme transfers a P from a substrate molecule to an ADP (organic molecule generated as an intermediate) Oxidative Phosphorylation – powered by the redox reactions of the ETC (on the membranes) during chemiosmosis Photophosphorylation – generation of ATP in the light reactions using chemiosmosis

II. ATP, cont Substrate-Level Phosphorylation vs II. ATP, cont Substrate-Level Phosphorylation vs. Oxidative/Photo Phosphorylation

II. ATP, cont In a human, 10 million molecules of ATP are “made” and “used” per second!! We use 1 X 1025 (10,000,000,000,000,000,000,000,000 or 10 quadrillion) molecules of ATP per day!! That translates to 100 lbs of ATP . . . At any given moment, the amount present is ~ 2 oz!! A working muscle cell recycles its entire supply of ATP in less than a minute!! Bacteria contain a 1 second supply of ATP!!

III. ♪ ♫ THE CYCLE OF LIFE ♪ ♫ Photosynthesis 6CO2 + 6H2O + sun  C6H12O6 + 6O2 Occurs in the chloroplasts of plants Cellular Respiration C6H12O6 + 6O2  6CO2 + 6H2O + ATP Occurs in the mitochondria of plants and animals CO2 + H2O Organic molecules + O2

IV. ENERGY IN THE CELL Oxidation-Reduction Reactions Energy yield in catabolism comes from transfer of electrons Movement of electrons releases chemical energy of molecule Released energy used to generate ATP from ADP and Pi Known as redox reaction One molecule loses an electron and a 2nd molecule gains an e- Oxidation Electron donor (which is oxidized)is known as reducing agent (EX: glucose) Reduction Electron acceptor (which is reduced)is known as oxidizing agent (EX: O2) Electron movement in molecules often traced by changes in H atom distribution

IV. ENERGY IN THE CELL, cont Oxidation-Reduction Reactions, cont Reactants Products Becomes oxidized Becomes reduced Carbon dioxide Water Oxidizing agent - oxygen Reducing agent - methane

IV. ENERGY IN THE CELL, cont Importance of Electron Carriers Energy contained in molecules (for example, glucose) must be released in a series of steps Electrons released as hydrogen atoms with corresponding proton Hydrogen atoms are passed to an electron carrier Electron carriers are coenzymes “Carry” 2 electrons in the form of H-atoms Allow for maximum energy transfer, minimum energy loss

IV. ENERGY IN THE CELL, cont Electron Carriers NAD+ Nicotinamide adenine dinucleotide Electron acceptor in cellular respiration Reduced to _NADH_ FAD Flavin adenine dinucleotide Electron acceptor in Krebs Cycle Reduced to _FADH2__ NADP+ Nicotinamide adenine dinucleotide phosphate Electron acceptor in light reaction of photosynthesis Reduced to _NADPH_

IV. ENERGY IN THE CELL, cont A Closer Look at Electron Carriers Reduction of NAD+ Dehydrogenase oxidizes substrate by removing 2 H-atoms NAD+ is reduced, creating NADH + H+ NADH shuttles electrons to electron transport chain. Electrons “fall” down to oxygen in a series of steps, each releasing energy in small amounts.

V. PHOTOSYNTHESIS – AN OVERVIEW Photosynthesis – Process of capturing light energy and converting it to chemical energy Endergonic – b/c e- increase in potential energy as they move from water to sugar. Plants are _Producers_; also known as _Autotrophs_ Redox Reaction becomes oxidized 6CO2 + 6H2O + sunlight C6H12O6 + 6O2 becomes reduced (e- added) Water is split and e- are transferred with H+ to CO2, reducing it to sugar. 18

V. PHOTOSYNTHESIS – AN OVERVIEW Chloroplast Structure Thylakoids – Site of Light Reaction First step in photosynthesis Grana Stroma Site of Calvin Cycle Second step in photosynthesis

V. PHOTOSYNTHESIS – AN OVERVIEW, cont Location of Photosynthesis Occurs in region of leaf known as mesophyll Cells contain abundant chloroplasts CO2 enters leaf through openings known as stomata H2O enters via roots; transported up the xylem

V. PHOTOSYNTHESIS OVERVIEW, cont Oxidation Reduction 21

V. PHOTOSYNTHESIS OVERVIEW, cont Sunlight: giant thermonuclear reactor – energy comes from fusion reactions similar to those in a hydrogen bomb. When light hits matter, it can be reflected, transmitted, or absorbed.

VI. LIGHT REACTION OF PHOTOSYNTHESIS Occurs in thylakoid membranes Converts light energy to chemical energy Light energy Visible light is a small portion of the electromagnetic spectrum. Light absorbed by chlorophyll and other photosynthetic pigments to power reactions is not seen. Light not utilized by plant is reflected & seen by human eye. (Leaf appears green b/c it reflects green &absorbs red and blue light) Light energy measured in photons, which each have a fixed quantity of energy inversely related to the wavelength. 23

VI. LIGHT REACTION OF PHOTOSYNTHESIS, cont Photosynthetic pigments - (substances that absorb visible light) Chlorophyll a – absorbs mainly blue-violet and red light Chlorophyll b – absorbs mainly blue and orange light Cartenoids – other accessory pigments; expand spectrum of light energy that can be used for photosynthesis carotenoid xanthophyll Chlorophyll a Chlorophyll b

VI. LIGHT REACTION OF PHOTOSYNTHESIS, cont The ability of a pigment to absorb various wavelengths of light can be measured with a spectrophometer which directs beams of light of different wavelengths through a solution of pigment and measures light transmitted at each wavelength.

VI. LIGHT REACTION OF PHOTOSYNTHESIS, cont 26

VI. LIGHT REACTION OF PHOTOSYNTHESIS, cont A photon of light energy is absorbed by pigment molecule in Photosystem II. Energy is passes from one molecule to another until it reaches P680 - pair of chlorophyll a molecules. Electron in each is excited to higher energy state – transferred to primary electron acceptor. Water is split to replace electron lost by P680. O2 is released. H+ ions remain. 27

VI. LIGHT REACTION OF PHOTOSYNTHESIS, cont Excited electron moves from primary electron acceptor to Photosystem I via electron transport chain. As electron “falls”, energy is released. Used to synthesize ATP through chemiosmosis. Known as photophosphorylation

VI. LIGHT REACTION OF PHOTOSYNTHESIS, cont Light energy is transferred via light-harvesting complexes to P700 in Photosystem I. Excited electron is captured by primary electron acceptor. P700’s electron is replaced by electron transport chain on Photosystem II. Electron from P700 moves through a short electron transport chain, reducing NADP+ to NADPH. 29

VI. LIGHT REACTION OF PHOTOSYNTHESIS, cont Linear Electron Flow 30

VI. LIGHT REACTION OF PHOTOSYNTHESIS, cont Cyclic Electron Flow Alternative pathway seen in some bacteria, plants May be photoprotective in plants Only utilizes Photosystem I No NADPH production No O2 release Does generate ATP 31

VII. CALVIN CYCLE OF PHOTOSYNTHESIS Also known as Dark Reaction, Light-Independent Rxn Occurs in stroma of chloroplasts “Synthesis” part of photosynthesis; utilizes ATP, NADPH generated in Light Reaction + CO2 to produce organic molecules Anabolic; endergonic Requires enzyme Rubisco Three basic steps Carbon Fixation Reduction Regeneration of RuBP 32

VII. CALVIN CYCLE OF PHOTOSYNTHESIS, cont 33

VIII. PHOTORESPIRATION Counterproductive pathway that produces 2-C molecule, which is then released as CO2 Due to oxygen competing for active site of Rubisco Consumes ATP; decrease carbohydrate yield

VIII. PHOTORESPIRATION, cont Plant Adaptations 35

IX. CELLULAR RESPIRATION – AN OVERVIEW Process used by cells to convert chemical energy in glucose (and other molecules) to ATP Primarily takes place in mitochondria of eukaryotic cells Overall Reaction becomes oxidized C6H12O6 + 6O2  6CO2 + 6H2O + energy becomes reduced Steps in Cellular Respiration Glycolysis “Sugar-breaking” Initial breakdown of glucose to intermediate, some ATP Citric Acid Cycle Completes oxidation of glucose to CO2 Produces ATP, but more importantly provides high-energy electrons for etc Electron Transport Chain Oxidative Phosphorylation Highest ATP yield; uses energy released from downhill flow of electrons to generate ATP Citric Acid Cycle + Electron Transport Chain = Oxidative Respiration

IX. CELLULAR RESPIRATION OVERVIEW, cont

X. GLYCOLYSIS Occurs in cytosol of cell Does not require oxygen First part of pathway is energy investment phase Second part of pathway is energy pay-off phase Energy Investment Phase

X. GLYCOLYSIS, cont Energy Pay-Off Phase

X. GLYCOLYSIS, cont Summary of Glycolysis

XI. OXIDATIVE RESPIRATION 2 pyruvates formed from glycolysis still contain a tremendous amount of chemical energy If oxygen is available, pyruvate enters mitochondrion for citric acid cycle and further oxidation Upon entering mitochondrion but prior to entering citric acid cycle “Grooming” Step Carboxyl group of pyruvate is removed, given off as CO2 Remaining 2-C molecule is oxidized to acetate → NAD+ reduced to NADH + H+ Acetate binds to molecule known as Coenzyme A to form acetyl CoA

XI. OXIDATIVE RESPIRATION, cont Grooming Step

XI. OXIDATIVE RESPIRATION, cont In the citric acid cycle (AKA Krebs cycle, tricarboxylic acid cycle, TCA cycle), 2-C molecule goes through a series of redox rxns. Occurs in mitochondrial matrix Produces NADH, FADH2, ATP, and CO2. CoA is not actually a part of the reaction . . . it is recycled . . . remember, it is an enzyme!

XI. OXIDATIVE RESPIRATION, cont A Closer Look at the Citric Acid Cycle

XI. OXIDATIVE RESPIRATION, cont Electron Transport – Oxidative Phosphorylation Traditionally called Electron Transport, now more commonly called Oxidative Phosphorylation. Occurs in inner mitochondrial membrane Membrane organized into cristae to increase surface area Two components to Oxidative Phosphorylation Electron Transport Chain Chemiosmosis

XI. OXIDATIVE RESPIRATION, cont Electron Transport Chain Collection of molecules, each more electronegative than the one before it Molecules are reduced, then oxidized as electrons are passed down the chain Oxygen is ultimate electron acceptor Purpose is to establish H+ gradient on two sides of inner mitochondrial membrane Energy from “falling electrons” used to pump H+ from matrix into intermembrane space

XI. OXIDATIVE RESPIRATION, cont Chemiosmosis Enzyme complexes known as ATP synthases located in inner mitochondrial membrane H+ electrochemical gradient provides energy Known as proton motive force Movement of H+ ions through membrane rotates enzyme complex Rotation exposes active sites in complex ATP is produced from ADP and Pi

XI. OXIDATIVE RESPIRATION, cont A summary of electron transport . . .

XII. CELLULAR RESPIRATION – A SUMMARY Each NADH shuttled through ETC results in approximately _________ ATP Each FADH2 shuttled through ETC results in approximately _________ ATP. Total ATP Gain in Cellular Respiration = ____ (glycolysis) + ____ (citric acid cycle) + ____ (oxidative phosphorylation) = _____ ATP / glucose

XIII. CELLULAR RESPIRATION & OTHER FOOD MOLECULES

XIV. METABOLIC POISONS Blockage of Electron Transport Chain Inhibition of ATP Synthase “Uncouplers” Prevent creation of H+ ion gradients due to leakiness of mitochondrial membrane

XV. FERMENTATION Anaerobic pathway Occurs in cytosol Purpose In glycolysis, glucose is oxidized to 2 pyruvate, 2 NAD+ are reduced to 2 NADH, and there is a net gain of 2 ATP In oxidative respiration, NADH is oxidized back to NAD+ in electron transport chain If oxygen is not present, another mechanism must be available to regenerate NAD+ or glycolysis cannot continue In fermentation, pyruvate is reduced thereby oxidizing NADH to NAD+ Allows glycolysis and net gain of 2 ATP per glucose to continue

XV. FERMENTATION, cont

XV. FERMENTATION, cont