Chapter 07 - Dr. Bill Tyler's Website -...

1

Chapter 07

http://www.mobento.com/video/DiyoEA5Mc

Cellular Respiration

**Important study hints**

• Draw out processes on

paper and label

structures and steps

• Keep working on those

flash cards!

2 http://getyournotes.blogspot.com/2012/01/cellular-respiration-aerobic-and.html

3

Respiration

• Organisms can be classified

based on how they obtain energy:

– Autotrophs

• Able to produce their own organic

molecules through photosynthesis

– Heterotrophs

• Live on organic compounds

produced by other organisms

• All organisms use cellular

respiration to extract energy

from organic molecules

http://en.wikipedia.org/wiki/Heterotroph

4

Cellular respiration

• Cellular respiration is a series of

reactions…

– Oxidation – loss of electrons

– Reduction – gain of electron

– Dehydrogenation – lost electrons

are accompanied by protons

• A hydrogen atom is lost (1 electron,

1 proton)

http://chemwiki.ucdavis.edu/Analytical_Chemistry/Electrochemistry/Redox_Chemistry/Oxidizing_and_Reducing_Agents

5

Redox

• During redox reactions, electrons carry

energy from one molecule to another

– Redox reactions are often coupled with an

electron carrier (NAD+)

http://chemwiki.ucdavis.edu/Analytical_Chemistry/Electrochemistry/Redox_Chemistry/Oxidizing_and_Reducing_Agents

Reduced compound A

(reducing agent)

Oxidized compound B

(oxidizing agent)

B is reduced A is oxidized

A

A

B

B

e- e-

e- e-

6

Redox

• Nicotinamide adenosine dinucleotide (NAD+)

– An electron carrier

– NAD+ accepts 2 electrons and 1 proton from

another molecule to become NADH

– Reaction is reversible

Product

Enzyme

NAD+

NAD+ NADH NADH

2e–

H+

+H+

Energy-rich

molecule

NAD+

Reduction

Oxidation

H H

H H

H H

H H

As energy-rich

molecule is

oxidized,

NAD+ is

reduced to

NADH

7

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

Product

Enzyme

NAD+

NAD+ NADH NADH

2e–

H+

+H+

Energy-rich

molecule

NAD+

1. Enzymes that use NAD+

as a cofactor for oxidation

reactions bind NAD+ and the

substrate.

2. In an oxidation–reduction

reaction, 2 electrons and

a proton are transferred

to NAD+, forming NADH.

A second proton is

donated to the solution.

3. NADH diffuses away

and can then donate

electrons to other

molecules.

Reduction

Oxidation

H H

H H

H

H

H H

As energy-rich molecule is oxidized,

NAD+ is reduced to NADH

Note change

from textbook

• In overall cellular energy harvest

– Dozens of redox reactions take place

– Number of electron acceptors, including NAD+

• In the end, high-energy electrons from initial

chemical bonds have lost much of their energy

– Electrons are transferred to a final electron acceptor

8

AH

A

NAD+

NADH

BH

B

Oxidation Oxidation Reduction Reduction

9

• Aerobic respiration

– Final electron receptor is oxygen (O2)

• Anaerobic respiration

– Final electron acceptor is an inorganic molecule (not O2)

• Fermentation

– Final electron acceptor is an organic molecule, such as lactic acid or ethanol

Types of Cellular Respiration

10

Aerobic respiration

C6H12O6 + 6O2 6CO2 + 6H2O

• Free energy = – 686 kcal/mol of glucose

– Free energy can be even higher than this in a cell

– This large amount of energy must be released in small steps rather than all at once.

– C6H12O6 (general form for 6 carbon sugar such as glucose)

11

2e–

Electrons from food

High energy

Low energy

2H+ 1 / 2 O2

Energy released

for ATP synthesis

H2O


Electron carriers

• Many types of carriers used

– Soluble, membrane-bound, move within

membrane

• All carriers can be easily oxidized and

reduced

– Some carry just electrons, some electrons

and protons

– NAD+ acquires 2 electrons and a proton to

become NADH

12

13


H H

O

NH2 + 2H

CH2 O

O

O

H

H

NH2

H

H

N

N

N

CH2 O

O

O

H

H

NH2

O–

H

H

N N

N

H H O

N

N

H H

H

C C

O P

O P O– O P

O– O P

N N

OH

CH2

NADH: Reduced form of nicotinamide

O

O O

O

NAD+: Oxidized form of nicotinamide

Reduction

Oxidation

Adenine Adenine

OH OH

OH OH OH

OH OH

NH2 + H+

CH2

O–

14

ATP

• Cells use ATP to drive endergonic

reactions

– ΔG (free energy) = –7.3 kcal/mol

– Compare with ΔG from complete

combustion of glucose = –686 kcal/mol

http://fgamedia.org/faculty/cholcroft/Bio45/miscellaneous_web_pages/Lectures/Metabolism/Metabolism_Intro.html

Cellular reactions can’t use all

the energy of glucose breakdown

at once, so cells must use

stepwise breakdown and

intermediaries such as ATP

15

• 2 mechanisms for ATP synthesis

1. Substrate-level phosphorylation

• Transfer phosphate group directly from substrate

molecule to ADP

• During glycolysis and Krebs cycle

2. Oxidative phosphorylation

• ATP synthase uses energy from a proton gradient

in the electron transport chain

PEP

– ADP

Enzyme Enzyme

– ATP P P

P

Adenosine

16


PEP

– ADP

Enzyme Enzyme

– ATP P

P

P

Adenosine

17

Oxidation of Glucose

The complete oxidation of

glucose proceeds in

stages:

1. Glycolysis

2. Pyruvate oxidation

3. Krebs cycle

4. Electron transport

chain & chemiosmosis

http://www.mobento.com/video/DiyoEA5Mc

18

Outer

mitochondrial

membrane

Intermembrane

space

Mitochondrial

matrix

FAD O2

Inner

mitochondrial

membrane

Electron

Transport Chain Chemiosmosis

ATP Synthase

NAD+

Glycolysis

Pyruvate

Glucose

Pyruvate

Oxidation

Acetyl-CoA

Krebs

Cycle

CO2

ATP H2O

ATP

e–

e–

NADH

NADH

CO2

ATP

NADH

FADH2


H+

e–

19

Glycolysis • Converts 1 glucose (6 carbons) to 2

pyruvate (3 carbons)

• 10-step biochemical pathway

• Occurs in the cytoplasm

• 2 NADH produced by the reduction of NAD+

• Net production of 2 ATP molecules by substrate-level phosphorylation – (uses 2 ATPs and produces 4 total = 2

net ATPs)

• Fun fact – Only process that occurs in red blood

cells since they do not have mitochondria!

ATP

20


Glycolysis

NADH

Pyruvate Oxidation

ATP

Electron Transport Chain

Chemiosmosis

Krebs

Cycle

6-carbon sugar diphosphate

NAD+ NAD+

Pri

min

g R

ea

cti

on

s

Cle

ava

ge

O

xid

ati

on

an

d A

TP

Fo

rma

tio

n

NADH NADH

P P

P P

ATP ATP

ADP ADP

3-carbon sugar

phosphate

3-carbon sugar

phosphate

Pi Pi

ADP ADP

ATP ATP

ATP

ADP ADP

ATP

3-carbon

pyruvate

3-carbon

pyruvate

6-carbon glucose

(Starting material)

Glycolysis begins

with the addition of

energy. Two high-

energy phosphates

(P) from two

molecules of ATP

are added to the

6-carbon molecule

glucose, producing

a 6-carbon

molecule with two

phosphates.

Then, the 6-carbon

molecule with two

phosphates is split in

two, forming two

3-carbon sugar

phosphates.

An additional

Inorganic phosphate

( Pi ) is incorporated

into each 3-carbon

sugar phosphate. An

oxidation reaction

converts the two

sugar phosphates

into intermediates

that can transfer a

phosphate to ADP to

form ATP. The

oxidation reactions

also yield NADH

giving a net energy

yield of 2 ATP and 2

NADH.

21


NADH

NAD+

NADH

Pi NAD+

Glucose

Hexokinase

Phosphofructokinase

Glucose 6-phosphate

Fructose 6-phosphate

Fructose 1,6-bisphosphate

Isomerase Aldolase

Pyruvate Pyruvate

Enolase

Pyruvate kinase

AD P

10

Glu

co

se

Gly

ce

rald

eh

yd

e

3-p

ho

sp

ha

te

Pyru

va

te

Glycolysis: The Reactions Glycolysis

NADH

Pyruvate Oxidation

H2O

ATP

ADP


Chemiosmosis

Krebs

Cycle

ATP

ATP

Phosphoglucose

isomerase

Glyceraldehyde 3-

phosphate (G3P)

Dihydroxyacetone

phosphate

1. Phosphorylation of

glucose by ATP.

2–3. Rearrangement,

followed by a second

ATP phosphorylation.

4–5. The 6-carbon molecule

is split into two 3-carbon

molecules—one G3P,

another that is converted

into G3P in another

reaction.

6. Oxidation followed by

phosphorylation produces

two NADH molecules and

two molecules of BPG,

each with one

high-energy phosphate

bond.

7. Removal of high-energy

phosphate by two ADP

molecules produces two

ATP molecules and leaves

two 3PG molecules.

8–9. Removal of water yields

two PEP molecules, each

with a high-energy

phosphate bond.

10. Removal of high-energy

phosphate by two ADP

molecules produces two

ATP molecules and two

pyruvate molecules.

1,3-Bisphosphoglycerate

(BPG) 1,3-Bisphosphoglycerate

(BPG)

Glyceraldehyde

3-phosphate

dehydrogenase

Pi

ADP

Phosphoglycerate

kinase

ADP

ATP

3-Phosphoglycerate

(3PG)

3-Phosphoglycerate

(3PG)

2-Phosphoglycerate

(2PG)

2-Phosphoglycerate

(2PG)

H2O

ATP

Phosphoenolpyruvate

(PEP)

Phosphoenolpyruvate

(PEP)

ADP ADP

ATP ATP

Ph

os

ph

oe

no

l-

pyru

va

te

3-P

ho

sp

ho

-

gly

ce

rate

1,3

-Bis

ph

os

ph

o-

gly

ce

rate

Glu

co

se

6-p

ho

sp

ha

te

Fru

cto

se

6-p

ho

sp

ha

te

Fru

cto

se

1,6

-bis

ph

os

ph

ate

Dih

yd

rox

ya

ce

ton

e

Ph

os

ph

ate

2-P

ho

sp

ho

-

gly

ce

rate

CH2OH

O

CH2 O

O

P

CH2 O

O

P

CH2OH

O CH2 CH2 O

O

P P

CHOH

H

C O

CH2 O P

C O

O CH2 P

CH2OH

CHOH

O C O

CH2 O

P

P

CHOH

O–

C O

CH2 O P

H C O

O–

C O

CH2OH

P

C O

O–

C O

CH2

P

C O

O–

C O

CH3

8

9

10

7

4 5

3

2

1

6

Phosphoglyceromutase

22

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23

NADH must be recycled

• For glycolysis to continue, NADH must be recycled to NAD+ by either:

1. Aerobic respiration • Oxygen is available as the final

electron acceptor

• Produces significantly more ATP

2. Fermentation • Occurs when oxygen is not

available

• Organic molecule is the final electron acceptor

http://getyournotes.blogspot.com/2012/01/cellular-respiration-aerobic-and.html

24

Fate of pyruvate

• Depends on oxygen availability

– When oxygen is present,

pyruvate is oxidized to acetyl-

CoA which enters the Krebs

cycle

• Aerobic respiration

– Without oxygen, pyruvate is

reduced in order to oxidize

NADH back to NAD+

• Fermentation

http://getyournotes.blogspot.com/2012/01/cellular-respiration-aerobic-and.html

25


Without oxygen

NAD+

O2 NADH

ETC in mitochondria

Acetyl-CoA

Ethanol

NAD+

CO2

NAD+

H2O

Lactate

Pyruvate

Acetaldehyde NADH

NADH

With oxygen

Krebs

Cycle

– Without oxygen, pyruvate is reduced by

lactate or alcohol fermentation

• This oxidizes NADH back to NAD+

• This is important

because NAD+ must

be recycled so

glycolysis can

continue to operate

26

Pyruvate Oxidation

• In the presence of oxygen, pyruvate is

oxidized

– Occurs in the mitochondria in eukaryotes

• multienzyme complex called pyruvate dehydrogenase

catalyzes the reaction

– Occurs at the plasma membrane in prokaryotes

http://schoolworkhelper.net/cellular-respiration-glycolysis-pyruvate-kerbs-etc/

27

• For each 3-carbon pyruvate molecule: – 1 CO2

• Decarboxylation by pyruvate dehydrogenase

– 1 NADH

– 1 Acetyl-CoA which consists of 2 carbons from pyruvate attached to coenzyme A

• Acetyl-CoA proceeds to the Krebs cycle

Products of pyruvate oxidation

http://schoolworkhelper.net/cellular-respiration-glycolysis-pyruvate-kerbs-etc/

***Double each of

these products per

glucose molecule

28


Glycolysis

Pyruvate Oxidation

NADH

Krebs

Cycle


Chemiosmosis

Pyruvate Oxidation: The Reaction

NAD+

CO2

CoA

Acetyl Coenzyme A

Pyruvate

Pyru

vate

A

cety

l C

oe

nzym

e A

O

CH 3

C

O–

C O

S CoA

CH3

O C

NADH

Per glucose

molecule =

• 2 CO2

• 2 NADHs

• 2 Acetyl CoA

29

Krebs Cycle

• Oxidizes the acetyl group

from pyruvate

• Occurs in the matrix of the

mitochondria

• Biochemical pathway of 9

steps in three segments

1. Acetyl-CoA + oxaloacetate →

citrate

2. Citrate rearrangement and

decarboxylation

3. Regeneration of oxaloacetate

1

2 3

http://drchadedwards.com/244/energy-production-through-the-krebs-cycle/

30


CoA-

(Acetyl-CoA) CoA

4-carbon

molecule

(oxaloacetate) 6-carbon molecule

(citrate)

NAD +

NADH

CO2

5-carbon

molecule

NAD+

NADH

CO2

4-carbon

molecule

ADP + P

Krebs Cycle

FAD

FADH2

4-carbon

molecule

NAD+

NADH

ATP

Glycolysis

Pyruvate Oxidation


Chemiosmosis

ATP

4-carbon

molecule

Pyruvate from glycolysis is

oxidized Krebs Cycle into an

acetyl group that feeds into the

Krebs cycle. The 2-C acetyl group

combines with 4-C oxaloacetate to

produce the 6-C compound citrate

(thus this is also called the citric

acid cycle). Oxidation reactions

are combined with two

decarboxylations to produce

NADH, CO2, and a new 4-carbon

molecule. Two additional

oxidations generate another

NADH and an FADH2 and

regenerate the original 4-C

oxaloacetate.

NADH

FADH2

Krebs

Cycle

1

2

3

31

Krebs Cycle

• For each Acetyl-CoA

entering:

– Release 2 molecules of

CO2

– Reduce 3 NAD+ to 3

NADH

– Reduce 1 FAD (electron

carrier) to FADH2

– Produce 1 ATP

– Regenerate oxaloacetate

http://drchadedwards.com/244/energy-production-through-the-krebs-cycle/

32


Glycolysis

NADH

F ADH2

Pyruvate Oxidation

ATP

Krebs Cycle: The Reactions

Citrate synthetase

NAD+

NADH

H2O

NAD+

NADH

CO2

Isocitrate dehydrogenase

Fumarase

CoA-SH 1

2

Aconitase 3

4

8

9

7

CoA-SH

NAD+

CO2

5

6

NADH

CoA-SH

GDP + Pi

Acetyl-CoA

═

CH3 — C — S

O CoA —

Krebs

Cycle

Malate

dehydrogenase

-Ketoglutarate

dehydrogenase

Succinyl-CoA

synthetase

GTP

ATP

ADP

Succinate

dehydrogenase

FADH2

8–9. Reactions 8 and 9: Regeneration of

oxaloacetate and the fourth oxidation

7. Reaction 7: The third oxidation

6. Reaction 6: Substrate-level phosphorylation

5. Reaction 5: The second oxidation

4. Reaction 4: The first oxidation

2–3. Reactions 2 and 3: Isomerization

1. Reaction 1: Condensation

Electron T ransport Chain

Chemiosmosis

Oxaloacetate (4C)

CH2

O ═ C

COO—

COO—

—

—

—

Citrate (6C)

HO — C — COO—

COO—

COO—

CH2

CH2

—

—

—

—

Isocitrate (6C)

HC — COO—

COO—

COO—

CH2

HO — CH

—

—

—

—

-Ketoglutarate (5C)

CH2

COO—

COO—

CH2

C — O

—

—

—

—

Succinyl-CoA (4C)

CH2

COO—

S — CoA

CH2

C ═ O

—

—

—

—

Succinate (4C)

COO—

CH2

COO—

CH2

—

—

—

Fumarate (4C)

HC

CH

═

COO—

COO—

—

—

Malate (4C)

HO — CH

COO—

CH2

COO—

—

—

—

FAD

Per glucose

molecule, the

Krebs cycle

produces…

• 4 CO2

• 6 NADHs

• 2 FADH2

• 2 ATP

33

At this point

• Glucose has been oxidized to:

– 6 CO2 (byproduct of aerobic respiration)

– 4 ATP

– 10 NADH

– 2 FADH2

• Electron transfer has released 53 kcal/mol

of energy by gradual energy extraction

• Energy will be put to use to manufacture

ATP in ETC

These two types of electron carriers proceed to the electron transport chain

34

Electron Transport Chain (ETC)

• ETC is a series of membrane-bound electron carriers

• Embedded in the inner mitochondrial membrane

Mitochondrial matrix

NADH + H+ H2O

H+ H+

2H+ + 1 / 2 O2

2

NADH dehydrogenase bc1 complex

Cytochrome

oxidase complex

Inner

mitochondrial

membrane

Intermembrane space

a. The electron transport chain

NAD+

Q

C

e–

FADH2

H+

e– 2 2 e– 2 2

FAD

35

Electron Transport Chain (ETC)

• Electrons from NADH and FADH2 are transferred to complexes of the ETC

• Each complex…

– A proton pump creating proton gradient

– Transfers electrons to next carrier


NADH + H+ H2O

H+ H+

2H+ + 1 / 2 O2

2


Cytochrome

oxidase complex

Inner

mitochondrial

membrane

Intermembrane space


NAD+

Q

C

e–

FADH2

H+

e– 2 2 e– 2 2

FAD

36


Glycolysi s

Pyruvate Oxidatio n

Krebs

Cycle ATP


Chemiosmosis

ADP + Pi

ATP

synthase

b. Chemiosmosis

H+

H+ H+ ATP


NADH + H+ H2O

H+ H+

2H+ + 1 / 2 O2

2


Cytochrome

oxidase complex

Inner

mitochondrial

membrane

Intermembrane space


NAD+

Q

C

e–

FADH2

H+

e– 2 2 e– 2 2

FAD

Note that O2 is the final electron

acceptor (the reason we require

O2), combining with protons to

form H2O as a byproduct of

aerobic respiration.

Chemiosmosis

• Accumulation of protons (H+) in intermembrane

space drives protons into the matrix via diffusion

• Membrane relatively impermeable to ions

• Most H+ can only reenter matrix via ATP synthase

– Uses energy of gradient to make ATP from ADP + Pi

– Proton Motive Force

ADP + Pi

ATP

synthase

b. Chemiosmosis

H+

H+ H+ ATP


NADH + H+ H2O

H+ H+

2H+ + 1 / 2 O2

2


Cytochrome

oxidase complex

Inner

mitochondrial

membrane

Intermembrane space


NAD+

Q

C

e–

FADH2

H+

e– 2 2 e– 2 2

FAD

H+ H+

H+ H+ H+

H+

H+

H+

38

ADP + Pi

Catalytic head

Stalk

Rotor

H+

H+

Mitochondrial

matrix

Intermembrane

space

H+ H+

H+

H+ H+

ATP


39


H2O

CO2

CO2

H+

H+

2H+

+ 1 / 2 O2

H+

e–

H+

32 ATP

Krebs

Cycle

2 ATP

NADH

NADH

FADH2

NADH

Pyruvate

Oxidation

Acetyl-CoA

e–

Q

C

e–

Glycolysis

Glucose

Pyruvate

Note the location of each

component of cellular

respiration…glycolysis,

pyruvate oxidation, Krebs

cycle and ETC

Note where the electron

carriers transfer electrons

from…to the ETC

40

Please note that due to differing

operating systems, some animations

will not appear until the presentation is

viewed in Presentation Mode (Slide

Show view). You may see blank slides

in the “Normal” or “Slide Sorter” views.

All animations will appear after viewing

in Presentation Mode and playing each

animation. Most animations will require

the latest version of the Flash Player,

which is available at

http://get.adobe.com/flashplayer.

41

Energy Yield of Respiration

• Theoretical energy yield (these values vary from book to book)

– 38 ATP per glucose for bacteria

– 36 ATP per glucose for eukaryotes

• Actual energy yield

– 30 ATP per glucose for eukaryotes

– Reduced yield is due to… • “Leaky” inner membrane

• Use of the proton gradient for purposes other than ATP synthesis

42

Chemiosmosis

Chemiosmosis

2 5

2 3

6 15

2

2

2 5 NADH

NADH

NADH

Total net ATP yield = 32

(30 in eukaryotes)

ATP

ATP

ATP

ATP

ATP

ATP

Krebs

Cycle

Pyruvate oxidation

FADH2

Glycolysis 2

Glucose

Pyruvate

ATP


2.5 ATPs

per NADH

2.5 ATPs

per NADH

1.5 ATPs

per FADH2

??

43

Regulation of Respiration

• Examples of negative

feedback inhibition

• Two key control points

1. In glycolysis

• Phosphofructokinase is

allosterically inhibited by

ATP and/or citrate

Glucose

Acetyl-CoA



Pyruvate

Pyruvate Oxidation

Krebs

Cycle


and

Chemiosmosis

Citrate

ATP

NADH

Inhibits

Inhibits Inhibits

Phosphofructokinase

Pyruvate dehydrogenase

Glycolysis

ADP

Activates

44

Regulation of Respiration

• Two key control points

2. In pyruvate oxidation

• Pyruvate dehydrogenase

inhibited by high levels of

NADH

• Citrate synthetase

inhibited by high

levels of ATP

Glucose

Acetyl-CoA



Pyruvate

Pyruvate Oxidation

Krebs

Cycle


and

Chemiosmosis

Citrate

ATP

NADH

Inhibits

Inhibits Inhibits

Phosphofructokinase


Glycolysis

ADP

Activates

Glucose

Acetyl-CoA



Pyruvate

Pyruvate Oxidation

Krebs

Cycle


and

Chemiosmosis

Citrate

ATP

NADH

Inhibits

Inhibits Inhibits

Phosphofructokinase


Glycolysis

ADP

Activates

45


46

Oxidation Without O2

1. Anaerobic respiration

– Use of inorganic molecules (other than O2) as

final electron acceptor

– Many prokaryotes use sulfur, nitrate, carbon

dioxide or even inorganic metals

2. Fermentation

– Use of organic molecules as final electron

acceptor

47

Anaerobic respiration

• Methanogens

– CO2 is reduced to CH4 (methane)

– Found in diverse organisms including cows

• Sulfur bacteria

– Inorganic sulphate (SO4) is reduced to

hydrogen sulfide (H2S)

– Early sulfate reducers set the stage for

evolution of photosynthesis

49

Fermentation

• Reduces organic molecules

in order to regenerate NAD+

to supply glycolysis allowing

it to continue, even in

absence of O2

1. Ethanol fermentation

occurs in yeast

• CO2, ethanol, and NAD+

are produced

CO2

2 Acetaldehyde

2 AD P

2 Lactate

Alcohol Fermentation in Yeast

2 ADP

Lactic Acid Fermentation in Muscle Cells

2 NAD+

2 NAD+

2 NADH

2 NADH

2 ATP

2 ATP

C O

C O

O–

CH3

C O

H

CH3

C O

C O

CH3

O–

CH3

H C OH

C O

O–

H

2 Ethanol

H C OH

CH3

2 Pyruvate

2 Pyruvate

Glucose

Glucose

G

L

Y

C

O

L

Y

S

I

S

G

L

Y

C

O

L

Y

S

I

S

50

Fermentation

2. Lactic acid

fermentation

• Electrons are transferred

from NADH to pyruvate to

produce lactic acid

• Occurs in animal cells

(especially muscles, such

as during sprinting)

CO2

2 Acetaldehyde

2 AD P

2 Lactate


2 ADP


2 NAD+

2 NAD+

2 NADH

2 NADH

2 ATP

2 ATP

C O

C O

O–

CH3

C O

H

CH3

C O

C O

CH3

O–

CH3

H C OH

C O

O–

H

2 Ethanol

H C OH

CH3

2 Pyruvate

2 Pyruvate

Glucose

Glucose

G

L

Y

C

O

L

Y

S

I

S

G

L

Y

C

O

L

Y

S

I

S

51

CO2

2 Acetaldehyde

2 AD P

2 Lactate


2 ADP


2 NAD+

2 NAD+

2 NADH

2 NADH

2 ATP

2 ATP

C O

C O

O–

CH3

C O

H

CH3

C O

C O

CH3

O–

CH3

H C OH

C O

O–

H

2 Ethanol

H C OH

CH3

2 Pyruvate

2 Pyruvate

Glucose

Glucose

G

L

Y

C

O

L

Y

S

I

S

G

L

Y

C

O

L

Y

S

I

S


52

Anabolic and Catabolism Pathways

• Metabolic pathways are

linked to reversible

pathways of cellular

respiration

– Large molecules broken

down and rearranged –

catabolic pathways

– Most larger molecules

needed by the cell are

produced – anabolic

pathways

53

Example of Catabolism of Protein

• Amino acids undergo deamination to remove the

amino group (-NH2)

• Remainder of the amino acid is converted to a

molecule that enters glycolysis or the Krebs cycle

– Alanine is converted to pyruvate

– Aspartate is converted to oxaloacetate

C

HO O

HO O

C

C

HO O

O

C

C O

C H H

C H H C H H

C H H

C H2N H NH3

HO

Urea

Glutamate α-Ketoglutarate

54

C

HO O

HO O

C

C

HO O

O

C

C O

C H H

C H H C H H

C H H

C H2N H

NH3

HO

Urea

Glutamate α-Ketoglutarate


55

Catabolism of Fat

• Fats are broken down to fatty

acids and glycerol

– Fatty acids are converted to 2-C

acetyl groups by b-oxidation

– Oxygen-dependent process

• The respiration of a 6-carbon

fatty acid yields 20% more

energy than 6-carbon glucose

• Runs in reverse to produce

fats

CoA

Fatty acid

O O

— C — C — C —

═

H

H

—

═

—

ATP

NADH

H2O

Krebs

Cycle

PPi AMP +

FADH2

Fatty acid

2C shorter

CoA

CoA

Fatty acid

O H

H

— C — C — C —

—

—

H

H

—

═

—

Fatty acid

OH

O H

H

— C — C — C

—

—

H

H

—

—

CoA

FAD

Fatty acid

O H

— C ═ C — C —

—

H —

═

CoA

Fatty acid

O HO

H

— C — C — C —

—

—

H

H

—

═

—

CoA

NAD+

Acetyl-CoA

56


CoA

Fatty acid

O O

— C — C — C —

═

H

H

—

═

—

ATP

NADH

H2O

Krebs

Cycle

PPi AMP +

FADH2

Fatty acid

2C shorter

CoA

CoA

Fatty acid

O H

H

— C — C — C —

—

—

H

H

—

═

—

Fatty acid

OH

O H

H

— C — C — C

—

—

H

H

—

—

CoA

FAD

Fatty acid

O H

— C ═ C — C —

—

H —

═

CoA

Fatty acid

O HO

H

— C — C — C —

—

—

H

H

—

═

—

CoA

NAD+

Acetyl-CoA

57

Cell building blocks

Deamination b-oxidation Glycolysis

Oxidative respiration

Ultimate metabolic products

Acetyl-CoA

Pyruvate

Macromolecule

degradation

Krebs

Cycle

Nucleic acids Polysaccharides

Nucleotides Amino acids Fatty acids Sugars

Proteins Lipids and fats

NH3 H2O CO2


Reaction pathways

are reversible to

make & breakdown

most molecules

needed by cells

58

Evolution of Metabolism

• Hypothetical timeline

1. Ability to store chemical energy in ATP

2. Evolution of glycolysis • Pathway found in all living organisms

3. Anaerobic photosynthesis (using H2S)

4. Use of H2O in photosynthesis (not H2S) • Begins permanent change in Earth’s

atmosphere about 2.4 Bya

5. Evolution of nitrogen fixation

6. Aerobic respiration evolved most recently

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