Respiration

• Overview: Life Is Work• Overview: Life Is Work

• Living cells

– Require transfusions of energy from outside sources to perform their many taskssources to perform their many tasks

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• The giant panda• The giant panda

– Obtains energy for its cells by eating plants

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Figure 9.1

• Energy• Energy

– Flows into an ecosystem as sunlight and leaves as heat Light energy

ECOSYSTEMECOSYSTEM

CO + H O

Photosynthesisin chloroplasts

C ll lOrganic

+ OCO2 + H2O Cellular respiration

in mitochondria

molecules+ O2

ATP

powers most cellular work

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HeatenergyFigure 9.2

Capacity to do work

Kinetic energy› energy of motion› moving objects perform work by imparting motion to › moving objects perform work by imparting motion to

other matter› Water gushing through dam turn turbines› Light to power photosynthesis› Light to power photosynthesis

Potential energySt d › Stored energy

› Based on location or structure› Energy stored in molecules

Totality of an organism’s chemical processCATABOLIC PATHWAYSCATABOLIC PATHWAYS

Release energy by breaking down complex molecules to simpler compoundsmolecules to simpler compoundsCellular respiration

ANABOLIC PATHWAYSConsume energy to build complicated molecules f i l from simpler onesProtein synthesis from amino acids

ExergonicExergonic› Proceeds with a net release of energy› occurs spontaneously› “Downhill”

Endergonic› Absorbs free energy from its surrounding

St f › Stores free energy› Non spontaneous› “Uphill”› Uphill

Transfer of electrons from a LESS electronegative substance to a MORE

l i b ?electronegative substance?

Downhill reaction or Uphill reaction?

Adenosine TriphosphateImmediate source of energy that powers cellular work

Phosphates bonds are so fragile

V t bl- Very unstable

When ATP is hydrolyzed, it releases free energyenergy

Th ll l th t The cell couples the energy to endergonicendergonic process process by transferring a phosphate group from ATP to some phosphate group from ATP to some other molecule

PHOSPHORYLATIONPHOSPHORYLATION

Phosphorylated intermediate- more Phosphorylated intermediate more reactive (less stable)

-Aerobic respiration-Fermentation Fermentation

“The wholesale release of energy from fuel is difficult to harness efficiently for

i k”constructive work”

Cellular respiration does not oxidize glucose in one step

Three metabolic stages1. Glycolysisy y

› Cytosol› Breakdown of glucose into 2 molecules of pyruvate

2. Krebs cycle› Mitochondrial matrix› Decomposes pyruvate into CO› Decomposes pyruvate into CO2

3. Electron Transport chain and oxidative phosphorylationphosphorylation

› Inner membrane of mitochondria

Substrate phosphorylationphosphorylation› When any enzyme

transfers a phosphate group from a substrate to ADPADP

Oxidative phosphorylation› Electrons are passed from one electron acceptor › Electrons are passed from one electron acceptor

to another› Energy released at each step is used to make ATP› Accounts for 90% of ATP generated

1. Energy investment Phasegy2. Energy payoff phase

Glucose enters the cell

DEBIT: 2 ATP molecules

Ready for splitting

Downhill reaction

S b t t h h l ti

Water extraction forms double bond

Substrate phosphorylation

Aka Citric Acid Cycley

•Occurs in the inner membrane of mitochondria

Inc electronegativityInc electronegativity

Final electron acceptoracceptor

ETC makes no ATP directly

How does the mitochondrion couple ETC and energy release to ATP synthesis?gy y

CHEMIOSMOSIS

H+ gradient couples the redox reactions of ETC to ATP synthesisPROTON MOTIVE FORCE

NADH- 3 pumps= 3 ATPsNADH 3 pumps= 3 ATPsFADH2 – 2 pumps= 2 ATPs

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

Cellular respiration› Relies on oxygen to produce ATPyg p

In the absence of oxygenyg› Cells can still produce ATP through

fermentation

GlycolysisGlycolysis› Can produce ATP with or without oxygen, in

aerobic or anaerobic conditionsaerobic or anaerobic conditions› Couples with fermentation to produce ATP

Fermentation consists ofFermentation consists of› Glycolysis plus reactions that regenerate NAD+,

which can be reused by glyocolysiswhich can be reused by glyocolysis

In alcohol fermentation› Pyruvate is converted to ethanol in two steps,

one of which releases CO2

D i l ti id f t tiDuring lactic acid fermentation› Pyruvate is reduced directly to NADH to form

lactate as a waste productlactate as a waste product

Both fermentation and cellular respiration› Use glycolysis to oxidize glucose and other

organic fuels to pyruvate

Fermentation and cellular respiration› Differ in their final electron acceptorCellular respiration› Produces more ATP

• Pyruvate is a key juncture in catabolism• Pyruvate is a key juncture in catabolismGlucose

CYTOSOL

PyruvateNo O2 present O presentNo O2 presentFermentation

O2 presentCellular respiration

Ethanolor

lactate

Acetyl CoAMITOCHONDRION

CitricCitricacidcycle

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Figure 9.18

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Comparison of ETC in Photosynthesis and Respiration Respiration

Mitochondria ChloroplastMitochondriaElectrons from food molecules (oxidation

ChloroplastDo not need food to make ATPmolecules (oxidation

of food molecules)make ATP

light drives the gelectron flow down an ETC and H+ gradient formationformation.