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Chapter 6: Cellular Respiration

• Why do we eat?

What did you eat for breakfast?

• What types of macromolecules were in your breakfast?

• Where did the macromolecules (carbs, protein, fat) in your breakfast come from?

• Producers and Consumers• Autotrophs and Heterotrophs

+ sugar

• Where do the producers get their ‘breakfast’?

• Plants take in carbon dioxide (CO2) at their leaves

• Plants absorb water (H2O) at their roots

• The simple molecules CO2 and H2O have all of the atomsneeded to form glucose (C6H12O6), if rearranged

CO2

CO2 and H2OBreakfast is served

Is glucose likely to form spontaneously from water (H2O) and

CO2?• Why or why not?

CO2 C6H12O6H2O

+

2

Fuel molecules are rich in Chemical Energy (a form of Potential Energy)

Glucose or Fuel Molecules

Where does the energy come from?

CO2 C6H12O6H2O

+ + O2 as ‘waste’

Photosynthesis is an uphill climb!

• The energy of the sun is captured, or harnessed at the chloroplasts, and used to do work!

• Reminder…What is work?• What has been ‘moved’ uphill in photosynthesis?

• There is more chemical energy in the products of photosynthesis than in the reactants!

A little, green sugar producing factory

• All plants, some bacteria and some protisis, trap energy from sunlight and use it to build sugars, which they need to live and grow. This process is called photosynthesis.

• Nearly all life on Earth depends on photosynthesis. If plants stopped photosynthesising, animals would have no food, and the world would eventually run out of oxygen.

Energy Flow and Chemical Cycling in Ecosystems

Do animals take in all of this glucose, or do plants keep some for themselves? Why or why not?

• Energy flows through the ecosystem, beginning as light energy from the sun

• Light energy is transformed into chemical energy

• Some used to do work, and some transformed into heat

• Why heat?

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POP QUIZ• Which living organisms have chloroplasts?

• All living things grow, and do cellular work, correct? We know that growth requires energy. All living things are capable of acquiring energy to do work.

• Hmm, then, do all living things undergo some form of cellular respiration. Yes or No?

Tomorrow we will learn that cellular respiration has 3 major steps. The first step,

glycolysis, occurs in the cytoplasm, and yields a little bit of ATP.

Cellular Respiration

• The process by which energy is harvested from the breakdown of food and converted into the energy of ATP

• This process is most efficient in the presence of oxygen (O2) but can occur in its absence– Aerobic respiration– Anaerobic respiration (fermentation)

Burning Fuel• Notice there are many arrows in this

equation.• Cellular Respiration breaks down glucose in a

highly regulated, multi-step process• Why not just one step? • Why not just light glucose on fire?

• During cellular respiration, the hydrogen from glucose (and an electron) is being transferred to oxygen

• This is also a transfer of electron(s), TO oxygen, from glucose.

• The electron(s) are moving to a MORE electronegative atom, Oxygen. Oxygen will hold on to these electrons(s) very tightly.

e-+

e-

H

• Recall that oxygen is a highly electronegative atom

• Energetically, it is much more difficult to move an electron (an electron and H) away from oxygen than it is to move an electron (and H) away from a carbon atom

• Thus, electrons held by oxygen are lower on the energy ‘hill’ than electrons associated with carbon in a fuel molecule

OXYGENH

O

H

4

H

H

Energy must be added to pull an electron away from an atom. The more electronegative the atom, the more energy is required to take an electron away from it

e-

O

C

e-Very stable bond

Less stable bond

Pot

entia

l E

nerg

y

H

H

H

How great is this potential energy difference? An electron equally shared between Hydrogen and Carbon vs. an electron being ‘hogged’ when bound to Oxygen?

e-

O

C

e-

Very stable bond

Less stable bond

Pot

entia

l E

nerg

y

H

A LOT! A rapid electron fall• A balloon is filled with

HYDROGEN GAS H2• This is similar to the

arrangement of C-H

• A match is touched to the balloon (a catalyst to get the reaction going)

• Hydrogen gas reacts with Oxygen in the air and causes an explosiong. All of the energy is given off as HEAT.

• (think Hindenburg, except on a smaller scale).

• Energy is released when electrons are transferred from a less electronegative atom to a more electronegative atom

• (like from glucose to oxygen-to make water)

• The electrons are now in a more ‘stable’environment, as more energy would be needed to pull them away from their current arrangement

Cellular Respiration is a collection of controlled Redox Reactions

•In cellular respiration, glucose is not burned in one step. Instead, the ELECTRONS from glucose are transferred, step-by-step to increasingly more electronegative atoms.

•The final electron (and H) acceptor is oxygen.

• Water is formed as a byproduct.

e-

e-

e-

e-

O2

e-

H2O

Cellular Respiration is a “Stepwise Energy Harvest”

“Stepwise Energy Harvest” via:

•Enzymes

• electron shuttlers (NADH)

• electron transport chain

e-

e-

e-

e-

O2

e-

5

Electrons are passed in “short’’ energy steps, down to oxygen

•Electrons are passed in ‘short’ steps from food (glucose) to electron shuttlers, and then to an electron transport chain

•Energy is ‘harnessed’along the way

Coupled Chemical Reactions

Which picture is similar to the balloon experiment?

Which picture is analogous to an electron transport chain? Why?

Coupled Chemical Reactions

ATP

ADP P

Electron Transport Chain

ATP

The Regeneration of ATP

ATP synthesis requires Energy

ATP hydrolysis yields Energy

How do reactions yield energy?

• Transfer of electrons during chemical reactions

• Relocation of electrons releases energy stored in organic molecules

• This energy is ultimately used to synthesize ATP

NH2

e-

ATP

Redox Reactions are a form of Energy Transfer

• The term “Redox” is a combination and abbreviation of two words:1. Reduction2. Oxidation

• These two chemical reactions always happen together

• The coupled gain and loss of ELECTRONS (e-s) • Electrons are negatively charged

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LEO the lion goes GER

• Loss of• Electrons is• Oxidation

• Gain of• Electrons is• Reduction

LEO GEROIL RIG

Oxidation Is Loss

Reduction IsGain

Bush and Co.

Redox Reactions

http://www.emc.maricopa.edu/faculty/farabee/BIOBK/redox.gif

Redox Reactions: Follow the electrons (e-)

http://www.emc.maricopa.edu/faculty/farabee/BIOBK/redox.gif

Redox Reactions

http://www.emc.maricopa.edu/faculty/farabee/BIOBK/redox.gif

In this example,

Compound B is

transformed into a new compound with a more

negative charge. Its

overall charge has

been reduced.

A Redox Reaction

• Na + Cl → Na+ Cl-

• Which atom is reduced?• Which atom is oxidized?

– Follow the electrons!

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A Redox Reaction

• Na + Cl → Na+ Cl-

• Which atom is reduced? Cl-• Which atom is oxidized? Na+

becomes oxidized

becomes reduced

Redox Reactions

• Loss or gain of electrons does not need to be complete

Cellular Respiration is a collection of Redox Reactions

C6H12O6 + 6O2 → 6CO2 + 6H2O + E

becomes oxidized

becomes reduced

Cellular Respiration is a collection of Redox Reactions

C6H12O6 + 6O2 → 6CO2 + 6H2O + E

During cellular respiration: Glucose is oxidized and Oxygen is reduced. Glucose ‘lost’ electrons, while oxygen gained electrons as water.

Cellular Respiration: A 3-part story Cellular Respiration: A 3 part

story

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Glycolysis: the splitting of sugar• First step in cellular respiration

• Occurs in the cytoplasm– The enzymes involved are dissolved in cytoplasm!

• INPUT: glucose, a 6 carbon sugar• Small amount of ATP added to start reaction• OUTPUT:

– 2 molecules of pyruvic acid (a 3 carbon molecule) – small amount of ATP– NADH!

2 Pyruvic

Acid

ATP

NADH

C

C

C

C

C

C

Glycolysis splits a six-carbon glucose into 2 three-carbon molecules

Glucose is first ‘energized’ with a phosphate. It has become momentarily less stable, energized.

ATP

2

P

P

ADP

C

C

C

C

C

C

ATP

2

ADP

A high-energy 6 carbon, glucose-like molecule

Glycolysis splits a six-carbon glucose into 2 three-carbon molecules

C

C

C

C

C

C

P

P

C

C

C

C

C

C

P

C

C

C

P

C

C

C

enzyme

Small amount of energy INPUT

ATP

2

ADP

Glycolysis splits a six-carbon glucose into 2 three-carbon molecules

2 Pyruvic Acid

ATP

ATP

2

2

NADH

YIELDS:

C

C

C

C

C

C

P

P

C

C

C

C

C

C

P

C

C

C

P

C

C

C

enzyme

C

C

C

C

C

C

Small amount of energy INPUT

NADH

What is the cab

carrying?

2Pyruvic Acid

Glycolysis Occurs in the Cytosol and does not require oxygen!

ATP2

NADH

YIELDS:

Glycolysis

C

C

C

C

C

C

C

C

C

C

C

C

Glycolysis generates a small amount of ATP

Direct phosphate transfer, enzyme mediated

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Glycolysis generates NADHNADH

e-What is meant

by a ‘high energy

electron’?

If an electron was ‘swiped’ or transferred to NADH from

glucose, what happened to

glucose during glycolysis? Was

it oxidized or reduced?

Later!

Glucose

2 Pyruvic acid

The book’s version

High Energy Electrons in the form of NADH and FADH2

NAD+ reduced

NAD+ + 2 e- + 1 H+ →NADH

FADH2

Cellular Respiration

Part 2: Krebs Cycle

• Where is this occuring?• What is a cycle?

Scary picture!

Part 2: Krebs Cycle

• Focus on outputs!!

4 + 2 = 64

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Part 2: Krebs Cycle

• NUMEROUS OXIDATION STEPS

• 6 Carbon molecule is oxidized to 2 molecules of CO2 6

Part 2: Krebs Cycle• Oxidiation steps produce energy in the form of ATP,

NADH, FADH2

• And the starting material (4 carbon molecule) is regenerated

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Where are the cabs (with e- s) going??

• NADH and FADH2 shuttle high energy electrons to an Electron Transport Chain

Part 3: Electron Transport Chain

• Where is this located, EXACTLY??

• What molecule sits at the bottom of the ‘chain’? – Hint: the molecule at the bottom is waiting,

and is very hungry for electrons

?

Electron Transport Chain

in the Inner Mitochondrial

Membrane

e-e-

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• Why is oxygen so important for cellular respiration?

• What function does the oxygen we BREATHE in have in this process?

OXYGENe- High energy electrons

• When high energy electrons are obtained by a protein, the protein may become ‘energized’

• These energized proteins have the capacity to do work!

• The work they will do?• Transport H+ against its concentration

gradiente-

e-

Before receiving e-

I’m feeling low onenergy.

I couldn’t possiblydo any WORK

H+

H+H+

H+

H+

H+

H+H+

H+

H+

H+

H+H+

Mitochondrial matrix

Intermembrane Space

H+H+H+H+

H+H+

e-

AFTER receiving e-

I’m energized, and ready to do

some WORK

e-Mitochondrial matrix

Intermembrane SpaceH+

H+H+ H+

H+

H+ H+

H+

H+ H+

H+H+

H+H+

H+H+

H+

H+

empty

• The work that is done is the pumping of H+ ions across the inner mitochondrial membrane AGAINST a concentration gradient!

e-

As electrons are passed along the ETC, H+ is pumped into the intermembrane space

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• This cellular work, has set up a H+ gradientacross the inner mitochondrial membrane

• Which way (into the matrix, or into the inner membrane space) do the H+ ions NOW want to diffuse?

ATP Synthase• The hydrogen ions will diffuse (rapidly) down

their concentration gradient• H+ diffuses through ATP Synthase, a membrane

protein that functions like our paddle wheel

The paddle wheel, and Star of the show!!

ATP Synthase is a mini-machine!

ATP Synthasecaptures the kinetic energy of H+ diffusion, and transforms it to synthesize ATP from ADP and P.

http://www2.nl.edu/jste/electron_transport_system.htm

http://www.biologie.uni-osnabrueck.de/biophysik/junge/pics.html

MOVIE TIME

Energetic Summary of Cellular Respiration

Can we generate ATP under anaerobic conditions? How?

• Aerobic= oxygen present• Anaerobic= without oxygen

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Does glycolysis require oxygen?

Does glycolysis produce ATP? If so, how much?

Krebs Cycle

Without oxygen, NADH cannot drop off its high energy electrons at the ETCSince oxygen is not ‘pulling’ electrons down the ETC, NADH (the electron carrier) fills up

In the absence of oxygen, NADH donates its high energy electrons to alternate substrates

Anaerobic Respiration: Lactic Acid Fermentation

Why do we continue to breath heavily even after we’ve

STOPPED exerting ourselves?

Anaerobic Respiration: Alcohol Fermentation

Are you thankful for yeast now??

Anaerobic RespirationAerobic cellular respirationutilizes OXYGEN as the final electron acceptor

Anaerobic respiration can occur with an alternate electron acceptor!

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Evolutionary Implications of Anaerobic Respiration

• Glycolysis is the most widespread metabolic pathway on Earth

• Glycolysis evolved very early

3.5 bya= bacterial fossils

2.7 bya= O2 accumulates

Does glycolysis require membrane bound organelles? Eukaryotic cells? ?

People can’t live on glucose

alone!!

Carbon fuel can come from macromolecules other than glucose

OUT?

Food

Polysaccharides Fats Proteins

Sugars Glycerol Fatty acids Amino acids

Amino groups

Glycolysis Acetyl-CoA

KrebsCycle Electron

Transport

cyanide

• Why is cyanide poisonous?

• How does cyanide actually KILL people, at the molecular level??