ELECTRON TRANSPORT AND CHEMIOSMOSIS

Cellular Respiration: Stage 4

Review: Stages of Cellular Respiration Glycolysis: occurs in cytosol.

Glucose 2 Pyruvate 2 ATP 2 NADH

Pyruvate Oxidation: occurs in matrix 2 Pyruvate 2 acetyl-CoA

2 NADH Krebs Cycle: occurs in matrix

2 acetyl-CoA 2 oxaloacetate (cycle) 6 NADH 2 FADH2 2 ATP

Stage 4: Electron Transport and Chemiosmosis NADH and FADH2 eventually transfer

their hydrogen atom electrons to series of compounds in the ETC.

Components of the ETC arranged in order of increasing electronegativity Weakest attractor of electrons at

beginning of chain Strongest at the end.

How it works...

Each component is alternatively reduced and oxidized Reduced: gains two electrons from

component before it in the chain Oxidized: by losing two electrons to

component after it in the chain. Like a baton being handed from

runner to runner in a relay race.

As Electrons shuttle through the ETC... Going from less stable to more stable Therefore, energy is _____________. This energy is used to move H+ ions

from the matrix into intermembrane space. Three proton pumps do this

At end of ETC...

Electrons very stable, therefore, extremely electronegative substance needed _______________ strips two electrons from

the final protein complex in the chain Two protons added from matrix to form

water. Oxygen is the FINAL ELECTRON

ACCEPTOR in the ETC.

Components of the ETC

1) NADH dehydrogenase2) Ubiquinone (Q) (Mobile Electron

Carrier)3) Cytochrome b-cl complex4) Cytochrome c (Mobile Electron

Carrier)5) Cytochrome oxidase complex

NADH gives up its two electrons to NADH dehydrogenase

Q and cytochrome cShuttle electrons from one carrier to another

Electrons reach final protein complex in the chain Cytochrome Oxidase

Complex Contains the enzyme

cytochrome oxidase: catalyzes the reaction between the electrons, protons, and molecular oxygen to form _________.

Yeah...so?

That’s great. We’ve used NADH to pump H+ ions into the intermembrane space.

Where’s the ATP?

The Point of the ETC

Highly exergonic: _____________________

Electrons: NADH oxygen. (∆ G) of -222 kJ/mol NADH.

Free energy converted to electrochemical potential energy: DUE TO THE PROTON GRADIENT

FORMING ACROSS THE INNER MITOCHONDRIAL MEMBRANE.

Electrochemical Potential Energy Type of energy stored by a battery Caused by accumulation of charged

objects (__________, __________, __________, etc.)

The energy becomes stored in the electrochemical gradient and will be used to power ATP synthesis in the next part of the process...____________________________________

NADH vs. FADH2

NADH passes electrons on to NADH dehydrogenase Therefore, oxeach NADH molecule will

help pump ________protons into the intermembrane space.

FADH2 passes electrons on to Q. Help pump _________ protons.

NADH vs. FADH2

NADH passes electrons on to NADH dehydrogenase Therefore, oxidation of each NADH

molecule will help pump ________protons into the intermembrane space.

RESULT: three ATP/coenzyme FADH2 passes electrons on to Q.

Oxidation of FADH2 will help pump _________ protons. RESULT: two ATP/coenzyme

Cytosolic NADH and Pyruvate Oxidation/Krebs NADH Cytosolic NADH is produced by

___________. May diffuse through outer membrane

into intermembrane space. Intermembrane is impermeable to NADH Glycerol-phosphate shuttle: transfers

electrons from cytosolic NADH to FAD to produce FADH2.

FADH2 transfers electrons to Q ____ ATP.

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Cyanide

Cyanide inhibits cytochrome oxidase activity

This prevents _____________ from acting as the final electron acceptor

Shuts down the ETC, H+ pumps, and consequently, ATP production.

Coma death Not poisonous to all organisms!

MIT-13 (anaerobic bacteria) live on cyanide. Used in the same way as aerobes use oxygen.

Importance of Cristae

Allows multiple copies of the ETC to be located throughout inner membrane.

... and finally... CHEMIOSMOSIS and OXIDATIVE ATP SYNTHESIS(but some terms first)

TERMINOLOGY Electrochemical Gradient: concentration

gradient created by pumping ions into a space surrounded by a membrane that is impermeable to ions.

Proton-motive force (PMF): a force that moves protons through an ATPase complex on account of the electrochemical gradient of proteins across a biological membrane.

ETC forms an Electrochemical Gradient Electrochemical gradient formed by ETC

Electrical component: higher positive charge in the _________________ space than the ________.

Chemical component: higher concentration of protons in the ____________space than the _____________.

Inner membrane impermeable to H+ ions. Intermembrane space becomes H+

reservoir. Potential difference (voltage) across inner

mitochondrial membrane.

Electrochemical Gradient drives Chemiosomosis Chemiosmosis: energy that drives synthesis

of ATP comes from the “osmosis” of protons. ____ forced to diffuse through protein

channels associated with ATP synthase (ATPase).

Electrochemical gradient looses potential energy which is converted to chemical potential energy: ATP!

This energy drives the synthesis of ADP + Pi ATP

Electrochemical Gradient and the Formation of ATP

Fate of ATP

ATP molecules transported through both mitochondrial _______________ by ____________ diffusion into the ____________ where they are used to drive ___________ processes such as movement, active transport, and synthesis reactions.

Relationship between ETC and Chemiosmosis? (review...) Electron transport chain obtains electrons from

hydrogen atoms from _________ and ____________ molecules.

At each sequential step in the ETC, electrons _________ energy by becoming more _____________.

Energy is harnessed by pumping _________ into the _____ reservoir.

________________ gradient is formed, which forces _______ to diffuse back into the mitochondrial matrix via a __________ complex.

Energy of gradient is ____________, and that energy is used to create ATP from _____ and ____.

Conditions Necessary for ETC and ChemiosmosisThis is a continuous process H+ reservoir must be maintained requires ____________

movement of __________ through the ETC dependant on availability of ______________ to act as the final electron acceptor. Hence, why we have lungs and fish have gills:

_______________________. Gas exchange in aerobic unicellular organisms?

Continuous source of electrons electrons are transferred via _______ and _______ coenzymes are formed during the first ____ stages of cellular respiration in the first three stages of cellular respiration, __________ is catabolized need of glucose means a need of _________. Hence, why heterotrophs must continually ____ and

photoautotrophs must continually ___________________.

Importance of Oxygen (in aerobes) No chemical is electronegative

enough to oxidize the last protein in the chain, except for oxygen.

If no oxygen no substance to act as final electon acceptor last protein can not be ‘freed up,’ ETC shuts down FADH2 and NADH can no longer be oxidized no NAD+ or FAD to recycle back into steps 1, 2 and 3.

Substrate-level vs. Oxidative PhosphorylationSubstrate-level Phosphorylation

Occurs in Glycolysis 2 ATP in step 7 and 2 ATP in step 10

Oxidative Phosphorylation Occur in

Pyruvate oxidation Krebs cycle Electron transport & Chemiosmosis

The Exergonic Flow of Electrons in Aerobic Respiration

What’s happening to the ‘lost’ energy?

THE ENERGETICS OF OXIDATIVE PHOSPHORYLATION (1) Water can be formed in a test tube by

combining hydrogen gas and oxygen gas.

Explosive reaction: bonding electrons move closer to a nucleus in water than in their reactant molecules.

But... Water is formed at the end of the ETC...WHY DON’T WE BLOW UP!?

THE ENERGETICS OF OXIDATIVE PHOSPHORYLATION (2) Electrons moving through the ETC occupying

more _______________ configurations as they move to ever more ___________ components.

Energy is ______________ at each step. Therefore, electrons in a very ____________

state at the end of the ETC. Electrons gain more _____________ when captured by oxygen.

Resulting formation of water is a low-energy emitting process.

THE ENERGETICS OF OXIDATIVE PHOSPHORYLATION (3)

ETC Videos

http://www.youtube.com/watch?v=_PgjsfY71AM

Seatwork/Homework Read page 109 – 110

Make notes and a diagram on the theoretical coenzyme and ATP yield. This is for YOU to study from!

Answer the following questions:1) The theoretical yield of ATP is 36. Give two reasons

why the actual yield may differ from this.2) What is the estimated number of ATP molecules

formed for each glucose molecule? Read the section on “Efficiency of Energy

Conversion...” Answer the following questions: 1) How is the efficiency of aerobic respiration

calculated? 2) How does the efficiency of aerobic respiration

differ from glycolysis?

Seatwork/Homework

Read the section “Metabolic Rate.” Make notes and answer the following questions:

1) What is metabolic rate?2) What is BMR? For humans, how much

energy does the BMR account for ? 3) What are some factors that effect the

BMR?4) What is a Benzinger calorimeter? Briefly,

how does it work?(skip the calculation)

Seatwork/Homework

Read the section on “Controlling Aerobic Respiration.” Answer the following questions:

1) What is phosphofructokinase? How does it regulate aerobic respiration? (in terms of ADP, ATP, and citrate).

2) How do NADH levels regulate respiration?