UNIT III – CELLULAR ENERGY Big Campbell ~ Ch 9, 10 Baby Campbell ~ Ch 6, 7

I. ♪ ♫ THE CYCLE OF LIFE ♪ ♫ Photosynthesis o Cellular Respiration o

II. ATP ATP → ADP + P i  ADP + P i → ATP   Mechanisms  Substrate-level Phosphorylation  Oxidative Phosphorylation  Photophosphorylation

II. ATP Substrate-Level Phosphorylation vs. Oxidative Phosphorylation

III. ENERGY IN THE CELL Oxidation-Reduction Reactions o Energy yield in catabolism comes from transfer of electrons o Movement of electrons releases chemical energy of molecule  Released energy used to generate ATP from ADP and P i o Known as redox reaction  One molecule loses an electron and a 2 nd molecule gains an electron  Oxidation – Loss of electron(s)  Reduction – Gain of electron(s)  Electron donor is known as reducing agent  Electron acceptor is known as oxidizing agent  Electron movement in molecules often traced by changes in H atom distribution

III. ENERGY IN THE CELL, cont Oxidation-Reduction Reactions, cont

III. ENERGY IN THE CELL, cont Importance of Electron Carriers o 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 o Electron carriers are coenzymes o “Carry” 2 electrons in the form of H-atoms o Allow for maximum energy transfer, minimum energy loss

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

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

IV. 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 Steps in Cellular Respiration  Glycolysis  “Sugar-breaking”  Initial breakdown of glucose to intermediate, some ATP  Citric Acid Cycle  Completes oxidation of glucose to CO 2  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

IV. CELLULAR RESPIRATION OVERVIEW, cont

V. 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

V. GLYCOLYSIS, cont Energy Pay-Off Phase

V. GLYCOLYSIS, cont Summary of Glycolysis

VI. 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 o “Grooming” Step  Carboxyl group of pyruvate is removed, given off as CO 2  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

VI. OXIDATIVE RESPIRATION, cont Grooming Step

VI. 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, FADH 2, ATP, and CO 2. CoA is not actually a part of the reaction... it is recycled... remember, it is an enzyme!

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

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

VI. 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

VI. 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 P i

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

VII. CELLULAR RESPIRATION – A SUMMARY Each NADH shuttled through ETC results in approximately _________ ATP Each FADH 2 shuttled through ETC results in approximately _________ ATP. Total ATP Gain in Cellular Respiration = ____ (glycolysis) + ____ (citric acid cycle) + ____ (oxidative phosphorylation) = _____ ATP / glucose

VIII. CELLULAR RESPIRATION & OTHER FOOD MOLECULES

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

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

X. FERMENTATION, cont

XI. PHOTOSYNTHESIS – AN OVERVIEW Photosynthesis – Process of capturing light energy and converting it to chemical energy Plants are __________________; also known as _____________ Redox Reaction Chloroplast Structure o Thylakoids – o Site of Light Reaction o First step in photosynthesis o Grana o Stroma o Site of Calvin Cycle o Second step in photosynthesis

XI. PHOTOSYNTHESIS – AN OVERVIEW, cont Location of Photosynthesis o Occurs in region of leaf known as mesophyll o Cells contain abundant chloroplasts o CO 2 enters leaf through openings known as stomata o H 2 O enters via roots

XI. PHOTOSYNTHESIS OVERVIEW, cont

XII. LIGHT REACTION OF PHOTOSYNTHESIS Occurs in thylakoid membranes Converts light energy to chemical energy Light energy o Visible light is a small portion of the electromagnetic spectrum. o 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. o Absorption spectrum – graph illustrating how different pigments absorb different wavelengths of light o Action spectrum – graph illustrating rate of photosynthesis vs wavelength o Light energy measured in photons. Photosynthetic pigments o Chlorophyll a – absorbs mainly blue-violet and red light o Chlorophyll b – absorbs mainly blue and orange light o Cartenoids – other accessory pigments; expand spectrum of light energy that can be used for photosynthesis

XII. 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. O 2 is released. H + ions remain.

XII. 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

XII. 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.

XII. LIGHT REACTION OF PHOTOSYNTHESIS, cont Linear Electron Flow

XII. LIGHT REACTION OF PHOTOSYNTHESIS, cont Cyclic Electron Flow oAlternative pathway seen in some bacteria, plants oMay be photoprotective in plants oOnly utilizes Photosystem I oNo NADPH production oNo O 2 release oDoes generate ATP

XIII. 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 + CO 2 to produce organic molecules Anabolic; endergonic Requires enzyme Rubisco Three basic steps  Carbon Fixation  Reduction  Regeneration of RuBP

XIII. CALVIN CYCLE OF PHOTOSYNTHESIS, cont

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

XIV. PHOTORESPIRATION, cont Plant Adaptations