Cellular RespirationHarvesting Chemical Energy

ATP

Harvesting stored energy• Energy is stored in organic molecules– carbohydrates, fats, proteins

• Heterotrophs eat these organic molecules food

Harvesting stored energy• Glucose is the model– catabolism of glucose to produce ATP

C6H12O6 6O2 ATP 6H2O 6CO2+ + +

CO2 + H2O + heatfuel(carbohydrates)

COMBUSTION = making a lot of heat energy by burning fuels in one step

RESPIRATION = making ATP (& some heat)by burning fuels in many small steps

CO2 + H2O + ATP (+ heat)

ATP

glucose

glucose + oxygen energy + water + carbondioxide

resp

iratio

n

O2 O2

+ heat

enzymesATP

How do we harvest energy from fuels?• Digest large molecules into smaller ones– break bonds & move electrons from one molecule

to another• as electrons move they “carry energy” with them• that energy is stored in another bond,

released as heat or harvested to make ATP

e-

+ +e-

+ –loses e- gains e- oxidized reduced

oxidation reduction

redox

e-

How do we move electrons in biology?

• Moving electrons in living systems– electrons cannot move alone in cells• electrons move as part of H atom• move H = move electrons

pe

+

H

+H

+ –loses e- gains e- oxidized reduced

oxidation reduction

C6H12O6 6O2 6CO2 6H2O ATP+ + +

oxidation

reductionH e-

Coupling oxidation & reduction• REDOX reactions in respiration – release energy as they breakdown organic molecules

• break C-C bonds• strip off electrons from C-H bonds by removing H atoms

– C6H12O6 CO2 = the fuel has been oxidized• electrons attracted to more electronegative atoms

– in biology, the most electronegative atom? – O2 H2O = oxygen has been reduced

– couple REDOX reactions & use the released energy to synthesize ATP

C6H12O6 6O2 6CO2 6H2O ATP+ + +

oxidation

reduction

O2

Oxidation & reduction• Oxidation– removing H – loss of electrons– releases energy– exergonic

• Reduction– adding H – gain of electrons– stores energy– endergonic

C6H12O6 6O2 6CO2 6H2O ATP+ + +

oxidation

reduction

Moving electrons in respiration• Electron carriers move electrons by

shuttling H atoms around– NAD+ NADH (reduced)– FAD+2 FADH2 (reduced)

+ Hreduction

oxidation

PO–

O–

O

–O

PO–

O–

O

–O

CC

O

NH2

N+

H

adenine

ribose sugar

phosphates

NAD+

nicotinamideVitamin B3niacin

PO–

O–

O

–O

PO–

O–

O

–O

CC

O

NH2

N+

HNADH

carries electrons as a reduced molecule

reducing power!

H

Overview of cellular respiration• 4 metabolic stages– Anaerobic respiration

1. Glycolysis– respiration without O2

– in cytosol

– Aerobic respiration– respiration using O2

– in mitochondria

2. Pyruvate oxidation3. Krebs cycle4. Electron transport chain

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

Glycolysis

glucose pyruvate2x6C 3C

• Breaking down glucose – “glyco – lysis” (splitting sugar)

– ancient pathway which harvests energy• where energy transfer first evolved• transfer energy from organic molecules to ATP• still is starting point for ALL cellular respiration

– but it’s inefficient • generate only 2 ATP for every 1 glucose

– occurs in cytosol

10 reactions– convert

glucose (6C) to 2 pyruvate (3C)

– produces: 4 ATP & 2 NADH

– consumes:2 ATP

– net yield: 2 ATP & 2 NADH

glucoseC-C-C-C-C-C

fructose-1,6bPP-C-C-C-C-C-C-P

DHAPP-C-C-C

G3PC-C-C-P

pyruvateC-C-C

Overview

DHAP = dihydroxyacetone phosphateG3P = glyceraldehyde-3-phosphate

ATP2

ADP2

ATP4

ADP4

NAD+2

2Pi

enzyme

enzyme

enzyme enzyme

enzyme

enzyme

enzyme

enzyme

2Pi2H

2

Glycolysis summary endergonicinvest some ATP

exergonicharvest a little ATP & a little NADH

net yield2 ATP2 NADH

4 ATP

ENERGY INVESTMENT

ENERGY PAYOFF

G3PC-C-C-P

NET YIELD

-2 ATP

Pi

3

6

4,5

ADP

NAD+

Glucose

hexokinase

phosphoglucoseisomerase

phosphofructokinase

Glyceraldehyde 3-phosphate (G3P)

Dihydroxyacetonephosphate

Glucose 6-phosphate

Fructose 6-phosphate

Fructose 1,6-bisphosphate

isomerase

glyceraldehyde3-phosphatedehydrogenase

aldolase

1,3-Bisphosphoglycerate(BPG)

1,3-Bisphosphoglycerate(BPG)

1

2

ATP

ADP

ATP

NADH

NAD+

NADH

Pi

CH2

C O

CH2OH

P O

CH2 O P

O

CHOH

C

CH2 O P

OCHOH

CH2 O PO

CH2OP

O

PO

CH2

H

CH2OHO

CH2 POO

CH2OH

P O

1st half of glycolysis (5 reactions)

Glucose “priming” get glucose ready to split

phosphorylate glucose molecular

rearrangement split destabilized glucose

2nd half of glycolysis (5 reactions)

7

8

H2O9

10

ADP

ATP

3-Phosphoglycerate(3PG)

3-Phosphoglycerate(3PG)

2-Phosphoglycerate(2PG)

2-Phosphoglycerate(2PG)

Phosphoenolpyruvate(PEP)

Phosphoenolpyruvate(PEP)

Pyruvate Pyruvate

phosphoglyceratekinase

phosphoglycero-mutase

enolase

pyruvate kinase

ADP

ATP

ADP

ATP

ADP

ATP

H2O

CH2OH

CH3

CH2

O-

O

C

PH

CHOH

O-

O-

O-

C

C

C

C

C

C

P

P

O

O

O

OO

O

CH2

NAD+

NADH

NAD+

NADH

Energy Harvest G3PC-C-C-P

PiPi 6

DHAPP-C-C-C

– NADH production• G3P donates H• oxidizes the sugar• reduces NAD+

• NAD+ NADH– ATP production

• G3P pyruvate• PEP sugar donates P

– “substrate level phosphorylation”

• ADP ATP

Substrate-level Phosphorylation

P is transferred from PEP to ADPkinase enzymeADP ATP

H2O9

10

Phosphoenolpyruvate(PEP)

Phosphoenolpyruvate(PEP)

Pyruvate Pyruvate

enolase

pyruvate kinaseADP

ATP

ADP

ATP

H2O

CH3

O-

O

C

O-

C

C

C

P

OO

O

CH2

• In the last steps of glycolysis, where did the P come from to make ATP?– the sugar substrate (PEP)

ATP

Energy accounting of glycolysis

• Net gain = 2 ATP + 2 NADH– some energy investment (-2 ATP)– small energy return (4 ATP + 2 NADH)

• 1 6C sugar 2 3C sugars

2 ATP 2 ADP

4 ADP

glucose pyruvate2x6C 3C

ATP4

2 NAD+ 2

7

8

H2O9

10

ADP

ATP

3-Phosphoglycerate(3PG)

3-Phosphoglycerate(3PG)

2-Phosphoglycerate(2PG)

2-Phosphoglycerate(2PG)

Phosphoenolpyruvate(PEP)

Phosphoenolpyruvate(PEP)

Pyruvate Pyruvate

ADP

ATP

ADP

ATP

ADP

ATP

H2O

NAD+

NADH

NAD+

NADH

PiPi 6

But can’t stop there!

• Going to run out of NAD+

– without regenerating NAD+, energy production would stop!

– another molecule must accept H from NADH• so NAD+ is freed up for another round

PiNAD+

G3P

1,3-BPG 1,3-BPG

NADH

NAD+

NADH

Pi

DHAP

raw materials products

NADH

pyruvate

acetyl-CoA

lactate

ethanol

NAD+

NAD+

NADH

NAD+

NADH

CO2

acetaldehyde

Krebscycle

lactic acidfermentation

with oxygenaerobic respiration

without oxygenanaerobic respiration“fermentation”

How is NADH recycled to NAD+?

Another molecule must accept H from NADH

recycleNADH

which path you use depends on who you are…

which path you use depends on who you are…

alcoholfermentation