2. Cellular respiration2

Chapter 9

Cellular Respiration:

Energy Flow in an Ecosystem

• _{Energy flows into an}

ecosystem as _________ and leaves as ??????

• ????????s generates oxygen and organic molecules

• _{?????????harvests the}

energy stored in organic molecules

– _{Uses this energy to}

regenerate ATP, which powers work

ECOSYSTEM Light energy

Photosynthesis in chloroplasts

Cellular respiration in mitochondria

Organic molecules+ O2

CO₂ + H₂O

ATP

powers most cellular work

Catabolic Pathways and Production of ATP

•

The breakdown of organic molecules is exergonic

occurs without oxygen

– _{Cellular respiration consumes oxygen and organic}

molecules and yields ATP

LE 9-5

2 H+ + 2 e– 2 H

(from food via NADH)

Controlled release of energy for synthesis of ATP ATP ATP ATP

2 H+

2 e–

H₂O

+ 1_{/2 O}

2 1/₂ O

2 H₂ +

1_{/2 O} 2

H₂O

Explosive release of heat and light

energy Cellular respiration Uncontrolled reaction F re e en er g y, G F re e en er g y,

G Ele

ct_ro n tr an sp o

rt _ch ain

The Stages of Cellular Respiration

•

Cellular respiration has three stages:

1. Glycolysis (breaks down glucose into two

molecules of pyruvate)

2. The citric acid cycle (completes the

breakdown of glucose)

3. Oxidative phosphorylation : accounts for

almost 90% of the ATP generated by cellular

respiration

• _{A small amount of ATP is formed in glycolysis and}

LE 9-6_3 Mitochondrion Glycolysis Pyruvate Glucose Cytosol ATP Substrate-level phosphorylation ATP Substrate-level phosphorylation Citric acid cycle ATP Oxidative phosphorylation Oxidative phosphorylation: electron transport and chemiosmosis Electrons carried via NADH Electrons carried via NADH and

LE 9-7

Enzyme

ADP P

Substrate

Product

Enzyme

ATP +

Glycolysis

• _{Glycolysis (“splitting of}

sugar”) breaks down

glucose into two molecules of pyruvate

• _{Glycolysis occurs in the}

cytoplasm and has two major phases:

– _{Energy investment phase} – _{Energy payoff phase}

http://www.science.smith.edu/depart ments/Biology/Bio231/glycolysis.html

Energy investment phase Glucose

2 ATP used 2 ADP + 2 P

4 ADP + 4 P 4 ATP formed

2 NAD+ _{+ 4 e}– _{+ 4 H}+

Energy payoff phase

+ 2 H+

2 NADH

2 Pyruvate + 2 H₂O 2 Pyruvate + 2 H₂O 2 ATP

2 NADH + 2 H+

Glucose 4 ATP formed – 2 ATP used 2 NAD+ + 4 e– + 4 H+

Class mini webquest

•

Go to this website:

•

http://programs.northlandcollege.edu/biology/

Biology1111/animations/glycolysis.html

•

Answer the following questions:

Between Glycolysis and The Citric Acid Cycle

1. CO₂ given off

2. Remaining molecule is oxidized to acetate

3. Coenzyme A (derived from a B vitamin) is added by an unstable, high energy bond

CYTOSOL

Pyruvate

NAD+

MITOCHONDRION

Transport protein

NADH + H+

Coenzyme A

The Citric Acid Cycle

• _{Takes place within}

the mitochondrial matrix

• _{Oxidizes organic fuel}

generating 1 ATP, 3 NADH, and 1 FADH₂ per turn

Pyruvate

(from glycolysis,

2 molecules per glucose)

ATP ATP ATP

Glycolysis Oxidation phosphorylation Citric acid cycle NAD+ NADH

+ H+

CO₂ CoA Acetyl CoA CoA CoA Citric acid

cycle 2CO2

3 NAD+

+ 3 H+

NADH 3

ATP

ADP + Pi

FADH₂

• TCA has eight steps

• each catalyzed by a

specific enzyme

• The acetyl group of acetyl CoA joins the cycle by

combining with

oxaloacetate, forming citrate

• The next seven steps

decompose the citrate back to oxaloacetate

• NADH and FADH₂ produced by the cycle relay electrons to the electron transport chain

ATP ATP ATP Glycolysis Oxidation phosphorylation Citric acid cycle Citric acid cycle Citrate Isocitrate Oxaloacetate Acetyl CoA

H2O

CO2

NAD+

NADH + H+

a-Ketoglutarate

CO2

NAD+

NADH + H+

Succinyl CoA Succinate GTP GDP ADP ATP FAD FADH2 Pi Fumarate

H₂O

Malate NAD+

NADH + H+

NAD+ and FADH+ in cellular respiration

• _{Electrons removed from organic compounds are often}

transferred to NAD+ _{(and FADH+) to make NADH}

• _{NADH (the ______form of NAD}+_{) represents stored energy}

NAD+

Nicotinamide (oxidized form)

Dehydrogenase 2e–_{+ 2 H}+

2 e–_{+ H}+

NADH H+

H+

Nicotinamide (reduced form) + 2[H]

End G,C thur, F, D after vids

•

http://www.youtube.com/watch?v=3OmMOcbT

qE4&feature=related

•

http

://ull.chemistry.uakron.edu/Pathways/Citric_aci

d_cycle/index.html

•

http://www.youtube.com/watch?v=FgXnH087JI

Stage a popbead drama!

•

Using popbeads design and then carry out a

simplified example of glycolysis and the Citric

Acid Cycle

•

Concentrate on inputs and outputs (what is

entering the process? What is produced by

the process?

– _{Hint: Designate a color popbead as a specific atom} – _{Hint: Only model the carbons in the citric acid}

Think

•

What are the ingredients? What are the

ATP ATP ATP Citric acid cycle Citrate Isocitrate Oxaloacetate Acetyl CoA

H2O

CO2 NAD+

NADH + H+

a-Ketoglutarate

CO₂ NAD+

NADH + H+

Succinyl CoA Succinate GTP GDP ADP ATP FAD FADH2 Pi Fumarate

H₂O

Malate NAD+

•

NADH and FADH

: donate

electrons to the ETC

•

The ETC is in the cristae of

the mitochondrion

– Most of the chain’s

components are proteins

– _{Electrons drop in free}

energy as they go down the chain

• finally passed to O₂, forming water NADH 50 FADH2 40 FMN Fe•S I _FAD Fe•S II III Q Fe•S Cyt b

30

20

Cyt c

Cyt c₁

Cyt a

Cyt a3

IV 10 0 Multiprotein complexes F re e en e rg y ( G ) re la ti ve t o O 2 ( kc al /m o l)

H2O

O2 2 H+ ₊ 1_/2

The electron transport chain

•

The electron transport chain generates no ATP

•

The chain’s function is to break the large

Chemiosmosis

• _{Electron transfer in the electron transport chain causes}

proteins to pump H+ _{from the mitochondrial matrix to}

the intermembrane space

• _H+ _{then moves back across the membrane, passing}

through channels in ATP synthase

• _{ATP synthase uses the exergonic flow of H}+ _{to drive}

phosphorylation of ATP

– _{This is an example of chemiosmosis, the use of energy in a}

LE 9-15

Protein complex of electron carriers

H+

ATP ATP ATP

Glycolysis phosphorylation:Oxidative electron transport and chemiosmosis Citric acid cycle H+ Q III I II FAD FADH2

+ H+

NADH NAD+ (carrying electrons from food) Inner mitochondrial membrane Inner mitochondrial membrane Mitochondrial matrix Intermembrane space H+ H+

Cyt c

IV

2H+ ₊ 1_{/2 O}

2 H2O

ADP +

H+

ATP ATP synthase

Electron transport chain

Electron transport and pumping of protons (H+_),

Which create an H+ _{gradient across the membrane}

P_i

Chemiosmosis

ATP synthesis powered by the flow of H+ back across the membrane

LE 9-14

INTERMEMBRANE SPACE H+ H+

H+ H

+ H+ H+ H+ H+ ATP MITOCHONDRAL MATRIX ADP + P i

A rotor within the membrane spins as shown when H+ _{flows past}

it down the H+

gradient.

A stator anchored in the membrane holds the knob stationary.

A rod (or “stalk”) extending into the knob also spins, activating catalytic sites in the knob.

•

http://

www.science.smith.edu/departments/Biology/B

io231/etc.html

•

http://vcell.ndsu.edu/animations/etc/movie-flas

An Accounting of ATP Production by Cellular Respiration

•

During cellular respiration, most energy flows in

this sequence:

glucose



NADH



electron transport chain



proton-motive force



ATP

•

About 40% of the energy in a glucose molecule

LE 9-16

CYTOSOL Electron shuttles

span membrane 2 NADH or 2 FADH₂

MITOCHONDRION Oxidative phosphorylation: electron transport and chemiosmosis 2 FADH₂

2 NADH 6 NADH

Citric acid cycle 2 Acetyl CoA 2 NADH Glycolysis Glucose Pyruvate2

+ 2 ATP

by substrate-level phosphorylation

+ 2 ATP

by substrate-level phosphorylation

+ about 32 or 34 ATP

by oxidation phosphorylation, depending on which shuttle transports electrons form NADH in cytosol

About 36 or 38 ATP Maximum per glucose:

Fermentation enables some cells to produce ATP without the use of oxygen

• Cellular respiration requires O₂ to produce ATP

• Glycolysis can produce ATP with or without O₂ (in aerobic or anaerobic conditions)

• Fermentation: In the absence of O₂, glycolysis couples with reactions that regenerate NAD+ to produce ATP

– _{Two common types are alcohol fermentation and}

Alcohol Fermentation

• _{In alcohol fermentation, pyruvate is converted to}

ethanol in two steps, with the first releasing CO₂

CO₂ + 2 H2 NADH+

2 NAD+

2 Acetaldehyde 2 ATP

2 ADP + 2P_i

2 Pyruvate

2

2 Ethanol

Alcohol fermentation

Lactic Acid Fermentation

• _{In lactic acid fermentation, lactate is an end product, with}

no release of CO₂

– _{Human muscle cells use lactic acid fermentation to generate ATP}

when O₂ is scarce

CO₂ + 2 H2 NADH+

2 NAD+

2 ATP 2 ADP + 2Pi

2 Pyruvate 2

2 Lactate

Lactic acid fermentation

Fermentation and Cellular Respiration

Compared

• _{Both processes use glycolysis}

to oxidize glucose and other organic fuels to pyruvate

• _{The processes have different}

final electron acceptors: an organic molecule (such as pyruvate) in fermentation and O₂ in cellular respiration

• _{Cellular respiration produces}

Facultative anaerobes can use fermentation

or cellular respiration

• _{Yeast and many}

bacteria are facultative anaerobes

– _{For them,}

pyruvate is a fork in the

metabolic road that leads to two alternative catabolic routes

Pyruvate Glucose

CYTOSOL

No O2 present Fermentation Ethanol or lactate Acetyl CoA MITOCHONDRION O2 present

Cellular respiration

Online quiz! End C wed

•

http://www.sciencegeek.net/Biology/review/

The Versatility of Catabolism

• Catabolic pathways funnel electrons from many kinds of organic molecules into cellular respiration

• _{Glycolysis: a wide range of}

carbohydrates

• Proteins:amino groups can feed glycolysis or the citric acid cycle

• _{Fats: glycerol can enter}

Biosynthesis (Anabolic Pathways)

• _{The body uses small molecules to build other}

substances

– _{These small molecules may come directly from food,}

• Feedback inhibition is the most common

mechanism for control

• If ATP concentration begins to drop,

respiration speeds up; ATP is abundant,

respiration slows down

• _{Control of catabolism:}

regulating the activity of enzymes in the

catabolic pathway Citric acid cycle Oxidative phosphorylation Glycolysis Glucose Pyruvate Acetyl CoA Fructose-6-phosphate Phosphofructokinase Fructose-1,6-bisphosphate – Inhibits ATP Citrate Inhibits Stimulates AMP + –

The Lab

•

C

H

O

+ 6 O



6H

O + 6 CO

•

PV=nRT

– _{So, if you keep temperature constant, the volume}

of the gas is directly proportional to the number of moles of gas present

•

CO

+ 2KOH



K

CO

(a solid!) + H

O

Data analysis

Temp. (degC)

Time (min)

Bead alone Germinating peas Dry peas + beads

Readi. Diff Reading Diff Corrected

Diff Reading Diff Correcteddiff

0 7.8 NA 8.8 NA NA NA NA

5 7.9 -0.1 8.6 0.2 0.2-(-0.1) 10 7.7 0.1 8.5 0.3