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Chapter 9

CELLULAR RESPIRATION

Relationship of Processes

Respiration: exergonic (releases E)

C6H12O6 + 6O2 6H2O + 6CO2 + ATP (+ heat)

Photosynthesis: endergonic (requires E)

6H2O + 6CO2 + Light C6H12O6 + 6O2

Cellular Respiration

complex process whereby cells make ATP by breaking

down organic compounds(glucose)

many rxns in aerobic respiration are redox: (one

reactant is oxidized while another is reduced)

location: mitochondrial cristae

Oxidation and Reduction

loses e- (donor)

gains e- (acceptor)

Not all electrons are transferred from one

substance to another, some change the degree of

e- sharing in covalent bonds.

Glucose Catabolism

Catabolic Pathway

Complex organic Simpler waste molecules products with less E

Some E used to do work

and dissipated as heat

Oxygen is extremely electronegative

Oxidation of glucose transfers e- to lower energy state-

does main work of respiration

releases energy to make ATP

** done in series of steps**

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Moving Electrons

Electrons cannot move alone in cells

• Move as part of H atom

• Energy is released as electrons “fall” from organic

molecule to O2.

Electron Carriers • Move electrons by shuttling H atoms around

NAD+ NADH

FAD+2 FADH2

NAD+

• Coenzyme (nicotinamide adenine dinucleotide)

• Electron acceptor- carries electrons to ETC

• Acts as an oxidizing agent during respiration

• Dehydroginase(enzyme)- catalyzes NAD+ NADH

NAD animation

Electron Transport Chain

• ETC breaks the fall of electrons of oxidation of

glucose into series of smaller steps

• Released energy is used to make ATP

• Extra energy is released as heat.

Glycolysis (glucose/splitting)

GLUCOSE(6C)is partially oxidized

end products: 2 PYRUVATE(3C), 2 NADH, 2 ATP

- occurs in cytosol

- 1st step: always occurs before

respiration or fermentation

- occurs in the absence of oxygen

- ancient pathway (early prokaryotes)

- inefficient

Glycolysis Overview

Stage 1: Energy Investment

• Cell uses ATP to

phosphorylate glucose

• Endergonic

Stage 2: Energy Payoff

• Two 3-C compounds oxidized

• Exergonic

Yield

2 pyruvate

2 NADH

2 ATP- substrate-level

phosphorylation

- Phosphate comes from sugar

substrate(PEP), not ETC

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Steps of Glycolysis

glycolysis animation

2 Possible Pathways for Pyruvate

If O2 present If no O2 present

respiration fermentation

(aerobic) (anaerobic respiration)

mitochondria cytosol

Stages of Cellular Respiration

1. Glycolysis

2. Citric Acid(Krebs)Cycle

3. Oxidative Phosphorylation

Cellular Respiration(aerobic)

C6H12O6 + 6 O2 6 H2O + 6 CO2 + 32 ATP

Process of breakdown of pyruvate in the

presence of oxygen

- prokaryotic cells: occurs in cytosol

- eukaryotic cells: occurs in mitochondria

- much more efficient than anaerobic

respiration

2 Major Stages of Respiration

1. Citric Acid Cycle

- oxidation of glucose is completed

- NADH and FADH2 are produced

2. Electron transport chain

- NADH is used to make ATP via oxidative phosphorolation

- location where most ATP is made

Location of Processes

Citric Acid Cycle

(matrix)

ETC

(inner

membrane of

cristae)

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Pyruvate oxidized to Acetyl CoA

Occurs before the Citric Acid Cycle

• 3 step oxidation process

• NAD+ reduced to NADH (acetate formed)

• Coenzyme A attached to acetate to form Acetyl CoA

• CO2 by-product is released into atmosphere

Pyruvate + CoA + NAD+ Acetyl CoA + CO2 + NADH

Citric Acid Cycle (Krebs Cycle) 2 pyruvate from glycolysis enter cycle

Occurs in mitochondrial matrix

Glucose is fully oxidized

animation

Oxidative Phosphorylation (production of ATP)

Electron Transport

Chain

• Occurs in inner membrane

of mitochondria

• Produces ATP by

oxidative

phosphorylation via

chemiosmosis

Chemiosmosis

• H+ ions pumped across

inner mitochondrial

membrane

• H+ ions diffuse through

ATP synthase to make

ATP

Electron Transport Chain

• Collection of molecules embedded in

inner membrane of mitochondria

• Tightly bound protein complexes

• FADH2 and NADH donate e- for

electron transport (redox rxns)

for ATP synthesis

• Does not make ATP directly, ATP

made through chemiosmosis

• O2 is final e- acceptor from H+

to form H2O

Oxidative Phosphorylation

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Energy Coupling of Chemiosmosis

How ATP Synthase Works

• H+ ions enter stator (1/2

channel) in membrane

• H+ ions enter rotor- changes

shape of subunits

– Rotor spins within membrane

• Each H+ ion makes one complete

turn

– Passes into matrix

• Turning of rod produces ATP from

ADP and Pi

animation ETC

Fermentation = glycolysis + regeneration of NAD+

1. Lactate Fermentation (animals)

- pyruvate converted to lactate

A. NADH is oxidized and donates its H to pyruvate

B. resultant NAD returns to glycolysis where it is reduced to NADH

C no release of CO2

** 2 ATP formed **

** process is CYCLICAL**

**lactate eventually diffuses into liver where it is converted back to pyruvate

when O2 again present **

2. Alcoholic Fermentation (yeasts, plant cells, microorganisms)

- pyruvate converted to ethanol

A. CO2 molecule is removed from pyruvate (3C) forming acetaldehyde

(2 C) B. acetyldehyde is reduced to form ethanol

2 H (from NADH + H ion) are added to 2C compound to form

ethanol

C. NAD is formed (back to glycolysis)

** 2 ATP formed **

** process is CYCLICAL**

**causes alcohol in beer and wine,

air bubbles in bread, beer, and wine**

NO ATP FORMED IN

FERMENTATION

PURPOSE OF FERMENTATION:

TO REGENERATE NAD FOR GLYCOLYSIS

2 ATP produce enough energy for prokaryotes and small

multi-cellular eukaryotes

Useful for anaerobes and facultative anaerobes

Very widespread metabolic pathway of Earth’s organisms

Alternative Energy Sources

What if the body runs out of sugar for

glycolysis? Can the body still make ATP?

YES

This is how the Atkins and South Beach diets

work.

They are low carb, high protein/fat diets.

Alternative Energy Sources

Fats as fuel:

• Glycerol PGAL glycolysis

• FA tails Acetyl CoA Krebs

Proteins as fuel:

• proteins amino acids

• Amino acids pyruvate or

acetyl CoA Krebs

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review animation

Biofeedback Regulation of

Cellular Respiration

Importance of Phosphofructokinase:

(regulates rate of respiration)

• Allosteric enzyme- receptors for

specific inhibitors and activators

• controls rate of glycolysis and

citric acid cycle

• Inhibited by ATP and citrate

citrate citric acid cycle

ATP glycolysis

• Stimulated by AMP

• AMP+ P + P ATP

Review of Respiration

Glycolysis

Citric Acid Cycle

Oxidative Phosphorylation

Electron Transport Chain Chemiosmosis