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

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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

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.

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)

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 unstableEasily broken by

HYDROLYSIS

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. 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 ♪ ♫

• Photosynthesiso 6CO2 + 6H2O + sun C6H12O6 + 6O2 o Occurs in the chloroplasts of plants

• Cellular Respirationo C6H12O6 + 6O2 6CO2 + 6H2O + ATPo Occurs in the mitochondria of

plants and animals

CO2 + H2O Organic molecules + O2

IV. 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 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)

o Electron movement in molecules often traced by changes in H atom distribution

IV. ENERGY IN THE CELL, cont

• Oxidation-Reduction Reactions, cont

Becomes oxidized

Becomes reduced

Reactants Products

Reducing agent -

methane

Oxidizing agent - oxygen

Carbon dioxide Water

IV. ENERGY IN THE CELL, cont

• Importance of Electron Carrierso 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 carriero Electron carriers are coenzymes o “Carry” 2 electrons in the form of H-atomso Allow for maximum energy transfer,

minimum energy loss

IV. ENERGY IN THE CELL, cont• Electron Carriers

Nicotinamide adenine dinucleotide

Electron acceptor in cellular respiration

Reduced to _NADH_ FAD

Flavin adenine dinucleotide Electron acceptor in Krebs Cycle Reduced to _FADH2__

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+

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.

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)

o Water is split and e- are transferred with H+ to CO2, reducing it to sugar.

Chloroplast StructureoThylakoids –

oSite of Light Reaction oFirst step in photosynthesis

oGranaoStroma

oSite of Calvin Cycle oSecond step in photosynthesis

V. PHOTOSYNTHESIS – AN OVERVIEW

V. 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; transported up the xylem

V. PHOTOSYNTHESIS OVERVIEW, contOxidation Reduction

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 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. (Leaf appears green b/c it reflects green &absorbs red and blue light)

o Light energy measured in photons, which each have a fixed quantity of energy inversely related to the wavelength.

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

Chlorophyll b

Chlorophyll a

xanthophyll

carotenoid

• 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.

• 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.

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.

Linear Electron Flow

• 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

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 FixationReductionRegeneration of RuBP

VII. CALVIN CYCLE OF PHOTOSYNTHESIS, cont

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, contPlant Adaptations

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, contEnergy 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 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

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

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

• 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

• 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

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”

o Prevent creation of H+ ion gradients due to leakiness of mitochondrial membrane

XV. 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

XV. FERMENTATION, cont

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

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