CELLULAR RESPIRATION:

AEROBIC HARVESTING

OF CELLULAR ENERGY

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Introduction

In chemo heterotrophs, eukaryotes

perform cellular respiration

That harvests energy from food

which

yields large amounts of ATP, that

allows for cellular work.

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Photosynthesis and cellular respiration-the

circle of life’s energy!

To reduce entropy and perform work, life requires

energy.

In almost all ecosystems, energy ultimately comes

from the sun, which is why we studied

photosynthesis first!

Key to remember……

glucose and oxygen are produced, so that’s

what we have to work with!

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Ultimately, Cells tap energy from electrons

“falling” from organic fuels to oxygen

The energy necessary for life is contained in the arrangement of

electrons in chemical bonds in organic molecules.

An important question is how do cells extract this energy?

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Where

Have we

Seen something

Like this

Before??!!

Final metabolic pathway is the Electron Transport Chain

We can harvest electrons from atoms to control the proton

energy that follows them around.

Have to be VERY careful to control these ions or acids can

build up!

We can do this with a semi-permeable membrane, enzymes

to control (transport) the electrons and resulting protons

Final, stable electron and proton acceptors.

Figure 6.5C

Controlledrelease ofenergy forsynthesisof ATP

NADH

NAD

H

H O2

H2O

2

2

2

ATP

21

Semi-permeable membrane-crista

Enzymes-to control (transport) the electrons and

resulting protons –mobile enzymes: Cytochrome Q

and Cytochrome C

Non-mobile enzymes; NADH Reductase,

Ubiquinone, (Collectively called “complexes”) and

then ATP Synthase used to place electrons on their

final acceptor in a process called “chemiosmosis”.

Ultimately, Cells tap energy from electrons “falling” from organic fuels to oxygen

When the carbon-hydrogen bonds of organic compounds are broken,

electrons are created and then transferred to a “final electron/proton”

acceptor.

An electron loses potential energy when it “falls” to oxygen.

What will use all this harvested electron/proton energy as it “falls” to

create?

Think about what you know and come up with a substance who can

donate Hydrogen?

Think about what you know and come up with a substance who can

accept Hydrogen?

How is this done? By shuttling the electrons

and protons found in hydrogen!

Cellular respiration is the changes in hydrogen atom distribution.

Glucose

loses its hydrogen atoms and

becomes oxidized to CO2.

Oxygen

gains hydrogen atoms and

becomes reduced to H2O.

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STAGES OF CELLULAR

RESPIRATION

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Overview: Cellular respiration occurs in

four main stages

Cellular respiration consists of a sequence of steps that can

be divided into three stages.

Stage 1 – Glycolysis-Cytosol

Stage 2 – Pyruvate processing-Bridge between

cytosol and mitochondrion

Stage 3- Citric acid cycle-Mitochondrion

Stage 4 – Oxidative phosphorylation with

chemiosmosis- Cristae

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Cellular respiration

Stage 1: Glycolysis

occurs in the cytoplasm and is anaerobic, it

begins cellular respiration, and

breaks down glucose into two molecules of a three-

carbon compound called pyruvate/pyruvic acid

Goal, break sugar to collect hydrogens

Net versus Gross ATP gains

C6H12O6+ 4 ADP +4 Pi + 2 ATP + 2 NAD

2 C3H5O3+ 4ATP+ 2 NADH+ 2 ADP + 2 Pi

Pyruvate/Pyruvic Acid has lots more bond energy that can

be extracted!

We need to stabilize the citric acid and make it permeable to the outer

mitochondrial membrane.

This second stage of cell respiration is a “bridge reaction” because

Nothing is produced, but we get the task done!

The first substance encountered in the mitochondria by

The acetyl-Coa is oxaloacetate.

Together they form a stable 6 carbon compound called

“citrate/citric acid”

Hence the next main stage of cell respiration is called

The “Citric acid cycle”.

Stage 2: The citric acid cycle

takes place in mitochondria,

breaks pyruvate to carbon dioxide, and

supply the next stage with electrons (NAD/FAD)

recycle pyruvic acid/pyruvate stabilizer (Co-A)

regenerate Acetyl –CoA acceptor-oxaloacetate

Goal is to collect hydrogens, make some ATP

(substrate) and release waste

Fourth and final stage of Cellular

respiration

Stage 3: Oxidative phosphorylation

involves electrons carried by NADH and

FADH2,

They shuttle H e- to the electron transport chain

embedded in the inner mitochondrial

membrane, (cristae)

involves chemiosmosis which is passing H e-

and H+ through ATP synthase (chemiosmosis)

together, they generate ATP through oxidative

phosphorylation.

Figure 6.10_1

H

H

H

H

H

H

H

H

H

H

H

Oxidative Phosphorylation

Electron Transport Chain Chemiosmosis

I

II

IIIIV

NADH NAD 2 H

FADH2 FAD

O2 H2O

ADP P ATP

21

Electronflow

Proteincomplexof electroncarriers

Mobileelectroncarriers

ATPsynthase

Most ATP production occurs by oxidative

phosphorylation

Oxidative phosphorylation

involves electron transport and chemiosmosis and

requires an adequate supply of oxygen.

Electrons from NADH and FADH2 travel down the electron transport

chain to from one enzyme to another using mobile enzymes to assist in

the electron moving properly.

Finally, in chemiosmosis, ATP synthase channels the H e- and following

H+ to O2 waiting in the matrix.

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Figure 6.12

NADH

FADH2

NADH FADH2NADH

orNADH

Mitochondrion

CYTOPLASM

Electron shuttlesacross membrane

Glycolysis

Glucose2

Pyruvate

PyruvateOxidation2 Acetyl

CoA

Citric AcidCycle

OxidativePhosphorylation

(electron transportand chemiosmosis)

Maximumper glucose:

by substrate-levelphosphorylation

by substrate-levelphosphorylation

by oxidativephosphorylation

2

2

2

2

6 2

ATP 2 about

28 ATP AboutATP32

ATP 2

ALL ROADS!

CONNECTION: Interrupting cellular respiration

can have both harmful and beneficial

effects

Three categories of cellular poisons obstruct the process of oxidative

phosphorylation. These poisons

1. block the electron transport chain (for example, rotenone, cyanide, and

carbon monoxide),

2. inhibit ATP synthase (for example, the antibiotic oligomycin), or

3. make the membrane leaky to hydrogen ions (called uncouplers, examples

include dinitrophenol).

Figure 6.11

ATPsynthase

NADNADH

FADH2 FAD

H

H

H

H

H

H H H

2 H

H2O ADP ATPP

O221

Rotenone Cyanide,carbon monoxide

Oligomycin

DNP

But once we are past glycolysis, what is the major

reactant needed to complete the remaining steps of

cellular respiration?

HINT:

FERMENTATION: ANAEROBIC

HARVESTING OF ENERGY

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Fermentation enables cells to produce

ATP without oxygen

Fermentation is a way of harvesting chemical energy that does not require

oxygen. Fermentation

takes advantage of glycolysis,

produces two ATP molecules per glucose, and

reduces NAD+ to NADH.

The trick of fermentation is to provide an anaerobic path for recycling

NADH back to NAD+.

Then, since we can’t effectively catabolize pyruvates, the animal cell does

what it can and produces Lactic acid and CO2.

Fully anaerobic creatures like fungi, convert glucose to ethanol and CO2

Fermentation enables cells to produce

ATP without oxygen

Lactate is carried by the blood to the liver, where it is converted back to

pyruvate and oxidized in the mitochondria of liver cells.

The dairy industry uses lactic acid fermentation by bacteria to make

cheese and yogurt.

Other types of microbial fermentation turn

soybeans into soy sauce and

cabbage into sauerkraut.

Figure 6.13B

2 NAD

2 NADH

2 NAD

2 NADH

2 Ethanol

2 Pyruvate

Glucose

2 ADP

2 ATP

2 P

Gly

co

lys

is

2 CO2

Fermentation enables cells to produce

ATP without oxygen

Obligate anaerobes-archae bacteria

are poisoned by oxygen, requiring anaerobic conditions, and

live in stagnant ponds and deep soils.

Facultative anaerobes

include yeasts and many bacteria, and

can make ATP by fermentation

6.14 EVOLUTION CONNECTION: Glycolysis

evolved early in the history of life on

Earth Glycolysis is the universal energy-harvesting process of life.

The role of glycolysis in fermentation and respiration dates back to

life long before oxygen was present,

when only prokaryotes inhabited the Earth,

about 3.5 billion years ago.

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