cellular respiration. cellular respiration – aka respiration the metabolic pathways by which...

Cellular Cellular RespirationRespiration

Cellular Respiration – Cellular Respiration – AKA Respiration AKA Respiration

The metabolic pathways by which The metabolic pathways by which carbohydrates are broken down into ATPcarbohydrates are broken down into ATP

The formula for respiration is:The formula for respiration is: CC66HH1212OO66 + 6O + 6O22 6CO 6CO22 + 6 H + 6 H22O + ATPO + ATP Respiration allows the gradual build up of Respiration allows the gradual build up of

ATP,ATP, If a cell used all the potential energy in If a cell used all the potential energy in

glucose at once, too much heat would be glucose at once, too much heat would be released, and not all the energy would be released, and not all the energy would be harvested.harvested.

Three Steps of Three Steps of RespirationRespiration

1.1. GlycolysisGlycolysis

Yields 2 molecules of ATPYields 2 molecules of ATP

2.2. Citric Acid Cycle (Krebs Cycle) Citric Acid Cycle (Krebs Cycle)


3.3. Electron Transport Chain (Oxidative Electron Transport Chain (Oxidative phosphorylation)phosphorylation)


Though 36 molecules of ATP are produced, it is Though 36 molecules of ATP are produced, it is only 39% of the total energy in a molecule of only 39% of the total energy in a molecule of glucoseglucose

The Process in GeneralThe Process in General

0 %

Electronscarried via NADH

Glycolysis

Glucose Pyruvate

Citricacidcycle

Oxidativephosphorylation:electron transport

andchemiosmosis

Electrons carriedvia NADH and

FADH2

Substrate-levelphosphorylation


Oxidativephosphorylation

ATP ATP ATP

GlycolysisGlycolysis

Glyco- of or relating to glucoseGlyco- of or relating to glucose Lysis- to split or burstLysis- to split or burst Changes one molecule of glucose to 2 Changes one molecule of glucose to 2

three Carbon molecules called three Carbon molecules called pyruvatepyruvate Occurs in the cytosol (cytoplasm)Occurs in the cytosol (cytoplasm) Does not require OxygenDoes not require Oxygen


Glucose Glucose 2 pyruvate 2 pyruvate 2 NAD 2 NAD 2 NADH 2 NADH 2 ADP2 ADP 2 ATP 2 ATP Net gain of 2 ATP molecules Net gain of 2 ATP molecules (top=input, (top=input,

bottom= outputs)bottom= outputs)

GlucoseGlucoseFructoseFructosePGALPGALPGAPGAPEPPEPpyrpyruvateuvate

4 ATP

2 ATP 2ADP

P + 2NAD2NADH

2 ATP

H2O 2 ATP


When Oxygen is present, glucose / When Oxygen is present, glucose / pyruvate can be broken down further pyruvate can be broken down further in a process called the Krebs cycle.in a process called the Krebs cycle.

However, when Oxygen is not present However, when Oxygen is not present pyruvate can be broken down through pyruvate can be broken down through the process of the process of fermentation.fermentation.

Aerobic respirationAerobic respirationrespiration with - respiration with OxygenOxygen

Anaerobic respirationAnaerobic respirationrespiration with - respiration with out Oxygenout Oxygen

The Evolutionary The Evolutionary Significance of GlycolysisSignificance of Glycolysis

Glycolysis occurs in nearly all organismsGlycolysis occurs in nearly all organisms Glycolysis probably evolved in ancient prokaryotes Glycolysis probably evolved in ancient prokaryotes

before there was oxygen in the atmospherebefore there was oxygen in the atmosphere

Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

FermentationFermentation

Glycolysis + the reduction of pyruvate Glycolysis + the reduction of pyruvate to lactic acid, alcohol, or COto lactic acid, alcohol, or CO2 2

Fermentation is inefficient. But when OFermentation is inefficient. But when O22 is not present it is better than nothing. is not present it is better than nothing. Glycolysis yields 2 ATP, fermentation yields Glycolysis yields 2 ATP, fermentation yields

2 more2 more Fermentation yields only 14.6 Kcal of a Fermentation yields only 14.6 Kcal of a

possible 686Kcal from 1 molecule of possible 686Kcal from 1 molecule of glucose that is about 2.1% efficient.glucose that is about 2.1% efficient.

FermentationFermentation

In yeast produces alcohol and COIn yeast produces alcohol and CO22 death death In humans produces lactic Acid In humans produces lactic Acid soreness soreness In athletes :In athletes :

because of training more mitochondria are because of training more mitochondria are produced in the muscle cells. produced in the muscle cells.

b/c of higher # of mito., they utilize more Ob/c of higher # of mito., they utilize more O22 and and can produce more ATP (less Ocan produce more ATP (less O22 wasted) wasted)

Means less Oxygen debt or deficitMeans less Oxygen debt or deficit Less fermentationLess fermentation Less sorenessLess soreness

Types of FermentationTypes of Fermentation

Fermentation consists of glycolysis plus Fermentation consists of glycolysis plus reactions that regenerate NADreactions that regenerate NAD++, which , which can be reused by glycolysiscan be reused by glycolysis

Two common types are alcohol Two common types are alcohol fermentation and lactic acid fermentationfermentation and lactic acid fermentation


In In alcohol fermentationalcohol fermentation, pyruvate is , pyruvate is converted to ethanol in two steps, converted to ethanol in two steps, with the first releasing COwith the first releasing CO22

Alcohol fermentation by yeast is used Alcohol fermentation by yeast is used in brewing, winemaking, and bakingin brewing, winemaking, and baking


Fig. 9-18

2 ADP + 2

Pi 2 ATP

Glucose

Glycolysis

2 NAD+

2 NADH

2 Pyruvate

+ 2 H+

2 Acetaldehyde

2 Ethanol

(a) Alcohol fermentation

2 ADP + 2

Pi2 ATP

Glucose

Glycolysis

2 NAD+

2 NADH+ 2

H+ 2 Pyruvate

2 Lactate

(b) Lactic acid fermentation

2 CO2

Fig. 9-18a

2 ADP + 2

P i 2 ATP

Glucose

Glycolysis

2 Pyruvate

2 NADH

2 NAD+

+ 2 H+

CO2

2 Acetaldehyde

2 Ethanol

(a) Alcohol fermentation

2

In In lactic acid fermentationlactic acid fermentation, pyruvate is , pyruvate is reduced to NADH, forming lactate as an reduced to NADH, forming lactate as an end product, with no release of COend product, with no release of CO22

Lactic acid fermentation by some fungi Lactic acid fermentation by some fungi and bacteria is used to make cheese and and bacteria is used to make cheese and yogurtyogurt

Human muscle cells use lactic acid Human muscle cells use lactic acid fermentation to generate ATP when Ofermentation to generate ATP when O22 is is scarcescarce


Fig. 9-18b

Glucose

2 ADP + 2

P i 2 ATP

Glycolysis

2 NAD+

2 NADH+ 2

H+ 2 Pyruvate

2 Lactate

(b) Lactic acid fermentation

Fermentation and Aerobic Fermentation and Aerobic Respiration ComparedRespiration Compared

Both processes use glycolysis to oxidize Both processes use glycolysis to oxidize glucose and other organic fuels to glucose and other organic fuels to pyruvatepyruvate

The processes have different final electron The processes have different final electron acceptors: an organic molecule (such as acceptors: an organic molecule (such as pyruvate or acetaldehyde) in fermentation pyruvate or acetaldehyde) in fermentation and Oand O22 in cellular respiration in cellular respiration

Cellular respiration produces 38 ATP per Cellular respiration produces 38 ATP per glucose molecule; fermentation produces glucose molecule; fermentation produces 2 ATP per glucose molecule2 ATP per glucose molecule


Obligate anaerobes Obligate anaerobes carry out carry out fermentation or anaerobic respiration fermentation or anaerobic respiration and cannot survive in the presence of Oand cannot survive in the presence of O22

Yeast and many bacteria are Yeast and many bacteria are facultative facultative anaerobesanaerobes, meaning that they can , meaning that they can survive using either fermentation or survive using either fermentation or cellular respirationcellular respiration

In a facultative anaerobe, pyruvate is a In a facultative anaerobe, pyruvate is a fork in the metabolic road that leads to fork in the metabolic road that leads to two alternative catabolic routestwo alternative catabolic routes


Fig. 9-19Glucose

Glycolysis

Pyruvate

CYTOSOL

No O2 present:Fermentation

O2 present:

Aerobic cellular respiration

MITOCHONDRIONAcetyl

CoAEthan

olor

lactate Citric

acidcycle

Aerobic Respiration Aerobic Respiration

Occurs when Oxygen is present Occurs when Oxygen is present Produces 36 ATP moleculesProduces 36 ATP molecules Begins after glycolysisBegins after glycolysis The The Transition reactionTransition reaction connects connects

glycolysis to the Aerobic pathways glycolysis to the Aerobic pathways (Krebs cycle & Electron transport (Krebs cycle & Electron transport chain).chain).

Transition Reactions Transition Reactions Connects glycolysis to the Krebs cycleConnects glycolysis to the Krebs cycle The pyruvate from glycolysis is converted The pyruvate from glycolysis is converted

to a 2 Carbon compound called an to a 2 Carbon compound called an acetyl acetyl groupgroup..

The acetyl group is attached to The acetyl group is attached to Coenzyme ACoenzyme A The resulting complex is The resulting complex is Acetyl Coenzyme Acetyl Coenzyme

AA (Acetyl CoA) (Acetyl CoA) CoenzymeCoenzyme- protein that acts as a carrier - protein that acts as a carrier

molecule in biochemical processes.molecule in biochemical processes. This process releases COThis process releases CO22

Transition Reaction Transition Reaction Occurs twice for each glucose moleculeOccurs twice for each glucose molecule Occurs in the matrix of the mitochondriaOccurs in the matrix of the mitochondria

2 pyruvate + 2 CoA 2 pyruvate + 2 CoA 2 Acetyl CoA + 2 2 Acetyl CoA + 2 COCO22

Mitochondrial structureMitochondrial structure Cristae - location of the electron transport Cristae - location of the electron transport

chainchain Cytosol – location of glycolysisCytosol – location of glycolysis Matrix- location of the transition reactions Matrix- location of the transition reactions

and the Krebs cycle.and the Krebs cycle.

2 NAD 2 NADH + H-

Fig. 9-10

CYTOSOL

MITOCHONDRION

NAD+

NADH + H+

2

1 3

PyruvateTransport protein

CO2

Coenzyme A

Acetyl CoA

Krebs CycleKrebs Cycle The products of the Transition RXN are the The products of the Transition RXN are the

reactants of the reactants of the Krebs CycleKrebs Cycle.. The The Krebs CycleKrebs Cycle is also known as the is also known as the Citric Citric

Acid CycleAcid Cycle. Citrate is the first metabolite . Citrate is the first metabolite produced in the Krebs Cycle.produced in the Krebs Cycle.

During the Krebs Cycle:During the Krebs Cycle: the acetyl group on Acetyl CoA is oxidized to CO2.the acetyl group on Acetyl CoA is oxidized to CO2. Some of the electrons (H ions) are accepted by NAD, Some of the electrons (H ions) are accepted by NAD, but 1 is picked up by another electron carrier, FAD.but 1 is picked up by another electron carrier, FAD. Some ATP is produced by phosphorylation like in Some ATP is produced by phosphorylation like in

glycolysis.glycolysis. The Krebs Cycle turns twice for each original The Krebs Cycle turns twice for each original

molecule of glucose.molecule of glucose.

Krebs CycleKrebs Cycle

InputsInputs 2 acetyl groups2 acetyl groups 2 ADP + 2 P2 ADP + 2 P 6 NAD6 NAD 2 FAD2 FAD

OutputsOutputs 4 CO4 CO22

2 ATP2 ATP 6 NADH6 NADH 2FADH2FADH22

See Figure 9.7

NADH

NAD+

CO2

CO2

Citrate

Oxaloacetate

Malate

Fumarate

Succinate

SuccinylCoA

ATP

ADP

NADH

NAD+

FAD

FADH2

H2O

NADH

NAD+

Acetyl CoA

CoA—SH

H2O

-Keto-glutarate

Isocitrate

Citricacidcycle

P

CoA—SH

CoA—SH

Fig. 9-7

ADPP

Substrate AT

P

+

Product

Substrate-level phosphorylation:

•Use of an enzyme to produce ATP and another product

The Electron Transport The Electron Transport ChainChain

Located in the cristaeLocated in the cristae Series of electron carriers that pass an Series of electron carriers that pass an

electron from one to another.electron from one to another. The electrons in the electron transport chain The electrons in the electron transport chain

come from NADH and FADHcome from NADH and FADH22 in the Krebs in the Krebs CycleCycle

Drives the process that generates most of the Drives the process that generates most of the ATP .ATP .

The process that generates most of the ATP is The process that generates most of the ATP is called oxidative phosphorylation because it is called oxidative phosphorylation because it is powered by redox reactionspowered by redox reactions

Electrons are transferred from NADH or Electrons are transferred from NADH or FADHFADH22 to the electron transport chain to the electron transport chain

Electrons are passed through a number of Electrons are passed through a number of proteins including proteins including cytochromes cytochromes (each with (each with an iron atom) to Oan iron atom) to O22

The electron transport chain generates no The electron transport chain generates no ATPATP

The chainThe chain’’s function is to break the large s function is to break the large free-energy drop from food to Ofree-energy drop from food to O22 into into smaller steps that release energy in smaller steps that release energy in manageable amountsmanageable amounts


Fig. 9-13

NADH

NAD+2FADH2

2 FAD Multiprot

eincomplexes

FAD

Fe•S

FMN

Fe•S

Q

Fe•S

Cyt b

Cyt c1 Cyt

cCyt a Cyt

a3

IV

Fre

e e

nerg

y (G

) re

lati

ve t

o O

2

(kcal /

mol )

50

40

30

20

10

2

(from NADHor FADH2)

0 2 H+ + 1/2

O2

H2

O

e–

e–

e–

Chemiosmosis: The Energy-Chemiosmosis: The Energy-Coupling MechanismCoupling Mechanism

Electron transfer in the electron transport Electron transfer in the electron transport chain causes proteins to pump Hchain causes proteins to pump H++ from the from the mitochondrial matrix to the intermembrane mitochondrial matrix to the intermembrane spacespace

HH++ then moves back across the membrane, then moves back across the membrane, passing through channels in passing through channels in ATP synthase ATP synthase

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

This is an example of This is an example of chemiosmosischemiosmosis, the use , the use of energy in a Hof energy in a H++ gradient to drive cellular gradient to drive cellular workwork

The energy stored in a HThe energy stored in a H++ gradient across gradient across a membrane couples the redox reactions a membrane couples the redox reactions of the electron transport chain to ATP of the electron transport chain to ATP synthesissynthesis

The HThe H++ gradient is referred to as a gradient is referred to as a proton-motive forceproton-motive force, emphasizing its , emphasizing its capacity to do workcapacity to do work


Fig. 9-14

INTERMEMBRANE SPACE

Rotor

H+

Stator

Internalrod

Cata-lyticknob

ADP+

P ATPi

MITOCHONDRIAL MATRIX

Oxidative Oxidative PhosphorylationPhosphorylation

The process by which ATP production The process by which ATP production is tied to an electron transport system is tied to an electron transport system that uses Oxygen as a final electron that uses Oxygen as a final electron receptor. receptor.

After Oxygen accepts the electron it After Oxygen accepts the electron it binds with Hydrogen from the matrix binds with Hydrogen from the matrix and form Hand form H22OO

Figure 9.8Figure 9.8

Complexes of the Electron Complexes of the Electron Transport ChainTransport Chain

NADH dehydrogenaseNADH dehydrogenase - causes the - causes the oxidation of NADH.oxidation of NADH.

Cytochrome b-c complexCytochrome b-c complex - the - the complex which receives electrons complex which receives electrons and pumps H ions into the inter-and pumps H ions into the inter-membrane space.membrane space.

Cytochrome oxidase complexCytochrome oxidase complex - - receives electrons and passes them receives electrons and passes them to oxygen.to oxygen.

Electron Transport ChainElectron Transport Chain

The Process in GeneralThe Process in General

0 %

Electronscarried via NADH

Glycolysis

Glucose Pyruvate

Citricacidcycle


andchemiosmosis

Electrons carriedvia NADH and

FADH2



Oxidativephosphorylation

ATP ATP ATP

The process with detailsThe process with detailsElectron shuttlesspan membrane

2 NADHor

2 FADH2

Citricacidcycle

2AcetylCoA

2 NADH 6 NADH 2 FADH2


andchemiosmosis

+ about 32 or 34 ATP+ 2 ATP+ 2 ATP

2Pyruvat

e

Glucose

Glycolysis

2 NADH

About36 or 38 ATP

Maximum per glucose:

MITOCHONDRION

CYTOSOL

Concept 9.6: Glycolysis Concept 9.6: Glycolysis and the citric acid cycle and the citric acid cycle connect to many other connect to many other

metabolic pathwaysmetabolic pathways Gycolysis and the citric acid cycle are major intersections Gycolysis and the citric acid cycle are major intersections to various catabolic and anabolic pathwaysto various catabolic and anabolic pathways


The Versatility of The Versatility of CatabolismCatabolism

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

Glycolysis accepts a wide range of Glycolysis accepts a wide range of carbohydratescarbohydrates

Proteins must be digested to amino Proteins must be digested to amino acids; amino groups can feed acids; amino groups can feed glycolysis or the citric acid cycleglycolysis or the citric acid cycle


Fats are digested to glycerol (used in Fats are digested to glycerol (used in glycolysis) and fatty acids (used in glycolysis) and fatty acids (used in generating acetyl CoA) generating acetyl CoA)

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

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


Fig. 9-20Proteins

Carbohydrates

Aminoacids

Sugars

Fats

Glycerol

Fattyacids

Glycolysis

Glucose

Glyceraldehyde-3-

Pyruvate

P

NH3

Acetyl CoA

Citric

acidcycle

Oxidativephosphorylati

on

Regulation of Cellular Regulation of Cellular Respiration via Feedback Respiration via Feedback

MechanismsMechanisms Feedback inhibition is the most Feedback inhibition is the most common mechanism for controlcommon mechanism for control

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

Control of catabolism is based mainly Control of catabolism is based mainly on regulating the activity of enzymes at on regulating the activity of enzymes at strategic points in the catabolic strategic points in the catabolic pathwaypathway


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