what do you know about cellular respiration?. shuttling energy sources across a membrane! different...

What do you know about Cellular Respiration?

Shuttling Energy Sources Across a Membrane!

• Different steps occur in different locations of a cell!

• Resources need to be moved across the mitochondrial membrane

What do you know about Cell Respiration?

Energy Flow in the EcosystemLightenergy

ECOSYSTEM

Photosynthesisin chloroplasts

Cellular respirationin mitochondria

CO2 H2O O2

Organicmolecules

ATP powersmost cellular workATP

Heatenergy

Catabolic Pathways and ATP Production

The breakdown of organic molecules is exergonic

Fermentation partial sugar degradation without O2

Aerobic respiration consumes organic molecules and O2 and yields ATP

Cellular Respiration

AKA Aerobic Respiration = REQUIRES O2 to complete!

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

-ΔG: -686kcal/mol

Redox Reactions: Oxidation and Reduction

The transfer of electrons during chemical reactions releases energy stored in organic molecules

This released energy is ultimately used to synthesize ATP

becomes oxidized(loses electron)

becomes reduced(gains electron)

The Principle of Redox: Transfer of Electrons!

•In oxidation, a substance loses electrons, or is oxidized (becomes more positive)

•In reduction, a substance gains electrons, or is reduced (the amount of positive charge is reduced)

More Redox!

becomes oxidized

becomes reduced

Electron donor is called the reducing agent Loses Electrons Oxidized (LEO)

Electron receptor is called the oxidizing agent Gains Electrons Reduced (GER)

Some redox reactions do not transfer electrons but change the electron sharing in covalent bonds

Redox of Methane and Oxygen Gas

Reactants Products

Energy

WaterCarbon dioxideMethane(reducing

agent)

Oxygen(oxidizing

agent)

becomes oxidized

becomes reduced

Oxidation of Organic Fuel Molecules During Cellular Respiration

Fuel (such as glucose) is oxidized, and O2 is reduced

In general lots of C-H bonds make a great fuel source

becomes oxidized

becomes reduced

Carbs: Why Are They Good Energy?Electrons are transferred in the form of H atoms.

C-H bonds are higher in energy. The more C-H bonds the more energy!

C6H12O6 CO2

O2 H2O

Loses Electrons

Gains Electrons

H is transferred from C to O, a lower energy state releases energy for ATP formation

Redox in Respiration Occur in Steps

Enzymes control release of energy by H transfer at key steps!

Not directly to O, but to coenzyme to make more energy first!

Nicotinamide(oxidized form)

NAD

(from food)

Dehydrogenase

Reduction of NAD

Oxidation of NADH

Nicotinamide(reduced form)

NADH

Nicotinamide Adenine Dinucleotide (NAD) and the Energy Harvesting

•Electrons from organic compounds are usually first transferred to NAD+, a coenzyme

•Each NADH (the reduced form of NAD+) represents stored energy that is tapped to synthesize ATP

Electron Removal From Glucose

Dehydrogenase

Sugar-source NAD+

Sugar-source NADH

Released into the surrounding solution

Energy Production in the Electron Transport Chain

(a) Uncontrolled reaction (b) Cellular respiration

Explosiverelease of

heat and lightenergy

Controlledrelease ofenergy for

synthesis ofATP

Fre

e en

erg

y, G

Fre

e en

erg

y, G

H2 1/2 O22 H 1/2 O2

1/2 O2

H2O H2O

2 H+ 2 e

2 e

2 H+

ATP

ATP

ATPE

lectron

transp

ort

chain

(from food via NADH)

The Stages of Cellular Respiration: A Preview

Glycolysis (color-coded teal) glucose to pyruvate 1.

Pyruvate oxidation and the citric acid cycle(color-coded salmon) completes glucose breakdown

2.

Oxidative phosphorylation: electron transport andchemiosmosis (color-coded violet) Most ATP synthesis

3.

Glycolysis

Electronscarried

via NADH

Glycolysis

Glucose Pyruvate

CYTOSOL

MITOCHONDRION

ATP

Substrate-levelphosphorylation

Figure 9.6-2

Electronscarried

via NADH

Electrons carriedvia NADH and

FADH2

Citricacidcycle

Pyruvateoxidation

Acetyl CoA

Glycolysis

Glucose Pyruvate

CYTOSOL MITOCHONDRION

ATP ATP



Figure 9.6-3

Electronscarried

via NADH

Electrons carriedvia NADH and

FADH2

Citricacidcycle

Pyruvateoxidation

Acetyl CoA

Glycolysis

Glucose Pyruvate

Oxidativephosphorylation:electron transport

andchemiosmosis

CYTOSOL MITOCHONDRION

ATP ATP ATP



Oxidative phosphorylation

© 2011 Pearson Education, Inc.

BioFlix: Cellular Respiration

A smaller amount of ATP is formed in glycolysis and the citric acid cycle by substrate-level phosphorylation

Substrate-level Phosphorylation

Substrate

Product

ADP

PATP

Enzyme Enzyme

Oxidative Phosphorylation

The sum of all the energy-releasing steps in the mitochondria accounts for almost 90% of the ATP generated

Energy Phases of Glycolysis

Energy Investment Phase

Glucose

2 ADP 2 P

4 ADP 4 P

Energy Payoff Phase

2 NAD+ 4 e 4 H+

2 Pyruvate 2 H2O

2 ATP used

4 ATP formed

2 NADH 2 H+

NetGlucose 2 Pyruvate 2 H2O

2 ATP

2 NADH 2 H+ 2 NAD+ 4 e 4 H+

4 ATP formed 2 ATP used

2 phases: Energy investmentEnergy Payoff

No Carbon released!

Does not depend on oxygen!

Figure 9.9-1

Glycolysis: Energy Investment Phase

ATPGlucose Glucose 6-phosphate

ADP

Hexokinase

1

Figure 9.9-2


ATPGlucose Glucose 6-phosphate Fructose 6-phosphate

ADP

Hexokinase Phosphogluco-isomerase

12

Figure 9.9-3


ATP ATPGlucose Glucose 6-phosphate Fructose 6-phosphate Fructose 1,6-bisphosphate

ADP ADP


Phospho-fructokinase

12 3

Figure 9.9-4


ATP ATPGlucose Glucose 6-phosphate Fructose 6-phosphate Fructose 1,6-bisphosphate

Dihydroxyacetonephosphate

Glyceraldehyde3-phosphate

Tostep 6

ADP ADP



Aldolase

Isomerase

12 3 4

5

Figure 9.9-5

Glycolysis: Energy Payoff Phase

2 NADH

2 NAD + 2 H

2 P i

1,3-Bisphospho-glycerate6

Triosephosphate

dehydrogenase

Figure 9.9-6


2 ATP2 NADH

2 NAD + 2 H

2 P i

2 ADP

1,3-Bisphospho-glycerate

3-Phospho-glycerate

2

Phospho-glycerokinase

67

Triosephosphate

dehydrogenase

Figure 9.9-7


2 ATP2 NADH

2 NAD + 2 H

2 P i

2 ADP


3-Phospho-glycerate

2-Phospho-glycerate

2 2


Phospho-glyceromutase

67 8

Triosephosphate

dehydrogenase

Figure 9.9-8


2 ATP2 NADH

2 NAD + 2 H

2 P i

2 ADP


3-Phospho-glycerate

2-Phospho-glycerate

Phosphoenol-pyruvate (PEP)

2 2 2

2 H2O



Enolase

67 8

9

Triosephosphate

dehydrogenase

Figure 9.9-9


2 ATP 2 ATP2 NADH

2 NAD + 2 H

2 P i

2 ADP


3-Phospho-glycerate

2-Phospho-glycerate

Phosphoenol-pyruvate (PEP)

Pyruvate

2 ADP2 2 2

2 H2O



Enolase Pyruvatekinase

67 8

910

Triosephosphate

dehydrogenase

Glycolysis


ATPGlucose Glucose 6-phosphate

ADP

Hexokinase

1

Fructose 6-phosphate

Phosphogluco-isomerase

2

Adds a phosphate = energizing the glucose

Isomerizes the sugar!


ATPFructose 6-phosphate

ADP

3

Fructose 1,6-bisphosphate


4

5

Aldolase

Dihydroxyacetonephosphate

Glyceraldehyde3-phosphate

Tostep 6Isomerase

Glycolysis

Second energy investment

Cuts the sugar in half!

Switches the 3C sugar between 2 forms


2 NADH2 ATP

2 ADP 2

2

2 NAD + 2 H

2 P i

3-Phospho-glycerate


Triosephosphate

dehydrogenase


67

Glycolysis

Removes 2 H to make an NADH and H+

Removes a phosphate to make ATP!


2 ATP

2 ADP2222

2 H2O

PyruvatePhosphoenol-pyruvate (PEP)

2-Phospho-glycerate

3-Phospho-glycerate

89

10


Enolase Pyruvatekinase

Glycolysis

Shuffles the phosphate to a different carbon

Pulls off water

Makes more ATP

Oxidation of Pyruvate to Acetyl CoA

This step is carried out by a multienzyme complex that catalyses three reactions to bring pyruvate into the mitochondria

Pyruvate

Transport protein

CYTOSOL

MITOCHONDRION

CO2 Coenzyme A

NAD + HNADH Acetyl CoA

1

2

3

Lose: 1 CO2 per pyruvateGain: 1 NADH per pyruvate

The Citric Acid Cycle

Completes the break down of pyruvate to CO2

The cycle oxidizes organic fuel derived from pyruvate, generating 1 ATP, 3 NADH, and 1 FADH2 per turn

REMEMBER 2 pyruvate per Glucose!

Pyruvate

NAD

NADH

+ HAcetyl CoA

CO2

CoA

CoA

CoA

2 CO2

ADP + P i

FADH2

FAD

ATP

3 NADH

3 NAD

Citricacidcycle

+ 3 H

• 8 steps, each catalyzed by a specific enzyme

• Acetyl combines with oxaloacetatecitrate

• The next seven steps decompose the citrate back to oxaloacetate, making the process a cycle

Overview: Citric Acid Cycle

1

Acetyl CoA

Citrate

Citricacidcycle

CoA-SH

Oxaloacetate

1

Acetyl CoA

CitrateIsocitrate

Citricacidcycle

H2O

2

CoA-SH

Oxaloacetate

1

Acetyl CoA

CitrateIsocitrate

-Ketoglutarate

Citricacidcycle

NADH+ H

NAD

H2O

3

2

CoA-SH

CO2

Oxaloacetate

1

Acetyl CoA

CitrateIsocitrate

-Ketoglutarate

SuccinylCoA

Citricacidcycle

NADH

NADH

+ H

+ H

NAD

NAD

H2O

3

2

4

CoA-SH

CO2

CoA-SH

CO2

Oxaloacetate

1

Acetyl CoA

CitrateIsocitrate

-Ketoglutarate

SuccinylCoA

Succinate

Citricacidcycle

NADH

NADH

ATP

+ H

+ H

NAD

NAD

H2O

ADP

GTP GDP

P i

3

2

4

5

CoA-SH

CO2

CoA-SH

CoA-SH

CO2

Oxaloacetate

1

Acetyl CoA

CitrateIsocitrate

-Ketoglutarate

SuccinylCoA

Succinate

Fumarate

Citricacidcycle

NADH

NADH

FADH2

ATP

+ H

+ H

NAD

NAD

H2O

ADP

GTP GDP

P i

FAD

3

2

4

5

6

CoA-SH

CO2

CoA-SH

CoA-SH

CO2

Oxaloacetate

1

Acetyl CoA

CitrateIsocitrate

-Ketoglutarate

SuccinylCoA

Succinate

Fumarate

Malate

Citricacidcycle

NADH

NADH

FADH2

ATP

+ H

+ H

NAD

NAD

H2O

H2O

ADP

GTP GDP

P i

FAD

3

2

4

5

6

7

CoA-SH

CO2

CoA-SH

CoA-SH

CO2

Oxaloacetate

NADH

1

Acetyl CoA

CitrateIsocitrate

-Ketoglutarate

SuccinylCoA

Succinate

Fumarate

Malate

Citricacidcycle

NAD

NADH

NADH

FADH2

ATP

+ H

+ H

+ H

NAD

NAD

H2O

H2O

ADP

GTP GDP

P i

FAD

3

2

4

5

6

7

8

CoA-SH

CO2

CoA-SH

CoA-SH

CO2

Oxaloacetate

Acetyl CoA

Oxaloacetate

CitrateIsocitrate

H2O

CoA-SH

1

2

Acetyl group (What’s left of the pyruvate) combines with Oxaloacetate to make Citrate

Citrate is isomerized by removing water and then adding it back

Isocitrate

-Ketoglutarate

SuccinylCoA

NADH

NADH

NAD

NAD

+ H

CoA-SH

CO2

CO2

3

4

+ H

Isocitrate is oxidized (Loses 2 H) and reduces NAD+A second reaction occurs, removing CO2

More CO2 is lost, and another NAD+ is reduced. Coenzyme A makes another appearance

Fumarate

FADH2

CoA-SH6

SuccinateSuccinyl

CoA

FAD

ADP

GTP GDP

P i

ATP

5

A phosphate group replaces CoA. The Phosphate is then transferred to GDP to make GTP

Succinate is oxidized by FAD to make FADH2

Oxaloacetate8

Malate

Fumarate

H2O

NADH

NAD

+ H

7 Water molecule added to rearrange bonds

Another redox to make NADH and oxaloacetate

The Pathway of Electron Transport

Occurs in the inner membrane (cristae) of the mitochondrion

Most of the chain’s components are proteins, which exist in multiprotein complexes

The carriers alternate reduced and oxidized states as they accept and donate electrons

NADH

FADH2

2 H + 1/2 O2

2 e

2 e

2 e

H2O

NAD

Multiproteincomplexes

(originally from NADH or FADH2)

III

III

IV

50

40

30

20

10

0

Fre

e e

ner

gy

(G)

rela

tiv

e to

O2 (

kcal

/mo

l)

FMN

FeS FeS

FAD

Q

Cyt b

Cyt c1

Cyt c

Cyt a

Cyt a3

FeS

Electrons are passed through a number of proteins including cytochromes (each with an iron atom) to O2

no ATP directly generated

Release energy in small steps

NADH and FADH2 Bring electrons to the ETC

Oxidative Phosphorylation and the ETC

Proteincomplexof electroncarriers

(carrying electronsfrom food)

Electron transport chain

Oxidative phosphorylation

Chemiosmosis

ATPsynth-ase

I

II

III

IVQ

Cyt c

FADFADH2

NADH ADP P i

NAD

H

2 H + 1/2O2

H

HH

21

H

H2O

ATP

Electron transfer is coupled with H+ pumping into intermembrane space of mitchondria

Chemiosmosis: Energy-Coupling Mechanism

Using H+ Gradient to do Work

INTERMEMBRANE SPACE

Rotor

StatorH

Internalrod

Catalyticknob

ADP+P i ATP

MITOCHONDRIAL MATRIX

The H+ gradient is referred to as a proton-motive force

H+ then moves back across the membrane, passing through the proton, ATP synthase

ATP synthase uses the exergonic flow of H+ to drive phosphorylation of ATP

H+ generated by ETC coupled with ATP synthesis!

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 34% of the energy in a glucose molecule is transferred to ATP during cellular respiration, making about 32-36 ATP

There are several reasons why the number of ATP is not known exactly

Figure 9.16

Electron shuttlesspan membrane

MITOCHONDRION2 NADH

2 NADH 2 NADH 6 NADH

2 FADH2

2 FADH2

or

2 ATP 2 ATP about 26 or 28 ATP

Glycolysis

Glucose 2 Pyruvate

Pyruvate oxidation

2 Acetyl CoACitricacidcycle

Oxidativephosphorylation:electron transport

andchemiosmosis

CYTOSOL

Maximum per glucose:About

30 or 32 ATP

Anaerobic Respiration

Oxygen is not used or may be poisonous!

Certain fungi and bacteria undergo Glycolysis coupled to an electron transport chain but use other molecules as final electron acceptors like sulfate!

Fermentation: Anaerobic Respiration Using Substrate Level Phosphorylation

Fermentation consists of glycolysis plus reactions that regenerate NAD+

Without NAD+ Glycolysis couldn’t happen

Fermentation

2 ADP 2 ATP

Glucose Glycolysis

2 Pyruvate

2 CO22

2 NADH

2 Ethanol 2 Acetaldehyde

(a) Alcohol fermentation (b) Lactic acid fermentation

2 Lactate

2 Pyruvate

2 NADH

Glucose Glycolysis

2 ATP2 ADP 2 Pi

NAD

2 H

2 Pi

2 NAD

2 H

In alcohol fermentation, pyruvate is converted to ethanol in two steps, with the first releasing CO2

In lactic acid fermentation, pyruvate is reduced to NADH, forming lactate with no release of CO2

2 ADP 2 P i 2 ATP

Glucose Glycolysis

2 Pyruvate

2 CO22 NAD

2 NADH

2 Ethanol 2 Acetaldehyde

(a) Alcohol fermentation

2 H

Figure 9.17a

(b) Lactic acid fermentation

2 Lactate

2 Pyruvate

2 NADH

Glucose Glycolysis

2 ADP 2 P i 2 ATP

2 NAD

2 H

Lactic acid fermentation by some fungi and bacteria is used to make cheese and yogurt, and human muscles when O2 is scarce

Importance of Pyruvate

Glucose

CYTOSOLGlycolysis

Pyruvate

No O2 present:Fermentation

O2 present: Aerobic cellular respiration

Ethanol,lactate, or

other products

Acetyl CoA

MITOCHONDRION

Citricacidcycle

Obligate anaerobes – Oxygen is poisonous!

Facultative anaerobes – can go either way

CarbohydratesProteins

Fattyacids

Aminoacids

Sugars

Fats

Glycerol

Glycolysis

Glucose

Glyceraldehyde 3- P

NH3 Pyruvate

Acetyl CoA

Citricacidcycle

Oxidativephosphorylation

Catabolism of Various Food

Sources

Glycolysis accepts a wide range of carbohydrates

Fatty acids are broken down by beta oxidation and yield acetyl CoA

An oxidized gram of fat produces more than twice as much ATP as an oxidized gram of carbohydrate

Biosynthesis (Anabolic Pathways)

The body uses small molecules to build other substances

These small molecules may come directly from food, from glycolysis, or from the citric acid cycle

Feedback Mechanisms and Cell Respiration

Phosphofructokinase

Glucose

GlycolysisAMP

Stimulates

Fructose 6-phosphate

Fructose 1,6-bisphosphate

Pyruvate

Inhibits Inhibits

ATP Citrate

Citricacidcycle

Oxidativephosphorylation

Acetyl CoA

•Feedback inhibition is the most common mechanism for control

•If ATP concentration begins to drop, respiration speeds up; when there is plenty of ATP, respiration slows down

Fermentation vs. Anaerobic vs. Aerobic Respiration

All use glycolysis (net ATP = 2) to oxidize glucose and harvest chemical energy of food

In all three, NAD+ is the oxidizing agent that accepts electrons during glycolysis

The processes have different final electron acceptors: an organic molecule (such as pyruvate or acetaldehyde) in fermentation and O2 in cellular respiration

Cellular respiration produces 32 ATP per glucose molecule; fermentation produces 2 ATP per glucose molecule

Figure 9.UN06

Inputs Outputs

GlucoseGlycolysis

2 Pyruvate 2 ATP 2 NADH

Figure 9.UN07

Inputs Outputs

2 Pyruvate 2 Acetyl CoA

2 OxaloacetateCitricacidcycle

2

26

8ATP NADH

FADH2CO2

Figure 9.UN08

Protein complexof electroncarriers

(carrying electrons from food)

INTERMEMBRANESPACE

MITOCHONDRIAL MATRIX

H

HH

2 H + 1/2 O2 H2O

NAD

FADH2 FAD

Q

NADH

I

II

III

IV

Cyt c

Figure 9.UN09

INTER-MEMBRANESPACE

HADP + P i

MITO-CHONDRIALMATRIX

ATPsynthase

H

ATP

Figure 9.UN10

Time

pH

dif

fere

nce

acro

ss m

emb

ran

e

Figure 9.UN11

what do you know about cellular respiration?. shuttling energy sources across a membrane! different...

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stored energy

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