UNIT III – CELLULAR ENERGY

Big Campbell ~ Ch 9, 10

Baby Campbell ~ Ch 6, 7

I. ♪ ♫ THE CYCLE OF LIFE ♪ ♫

• Photosynthesiso

o

• Cellular Respirationo

o

II. ATP

• ATP → ADP + Pi

• ADP + Pi → 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 electronso Movement of electrons releases chemical energy of molecule

Released energy used to generate ATP from ADP and Pi

o Known as redox reaction One molecule loses an electron and a 2nd 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-atomso 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 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

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, contEnergy 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 cycleo “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

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, FADH2, ATP, and CO2.

• 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

Phosphorylationo 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 ChainCollection 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 acceptorPurpose 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

• ChemiosmosisEnzyme 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

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

VII. 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

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

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 Structureo Thylakoids –

o Site of Light Reaction o First step in photosynthesis

o Granao Stroma

o Site of Calvin Cycle o Second step in photosynthesis

XI. PHOTOSYNTHESIS – AN OVERVIEW, cont

• Location of Photosynthesiso Occurs in region

of leaf known as mesophyll

o Cells contain abundant chloroplasts

o CO2 enters leaf through openings known as stomata

o H2O 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 pigmentso Chlorophyll a – absorbs mainly blue-violet and red lighto Chlorophyll b – absorbs mainly blue and orange lighto Cartenoids – other accessory pigments; expand spectrum of light energy

that can be used for photosynthesis

XII. LIGHT REACTION OF PHOTOSYNTHESIS, cont

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. O2 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

o Alternative pathway seen in some bacteria, plants

o May be photoprotective in plants

o Only utilizes Photosystem I

o No NADPH production

o No O2 releaseo Does 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 + CO2 to produce organic molecules

• Anabolic; endergonic• Requires enzyme Rubisco• Three basic steps

Carbon FixationReductionRegeneration of RuBP

XIII. CALVIN CYCLE OF PHOTOSYNTHESIS, cont

XIV. 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

XIV. PHOTORESPIRATION, contPlant Adaptations