Cellular Respiration Harvesting Chemical Energy

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Slide 10

Fig. 9-UN1

becomes oxidized

(loses electron)

becomes reduced

(gains electron)

Slide 11

Fig. 9-UN2

becomes oxidized

becomes reduced

Slide 12

The electron donor is called the reducing agent

The electron receptor is called the oxidizing agent

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

An example is the reaction between methane and O2

Slide 13

Fig. 9-3

Reactants

becomes oxidized

becomes reduced

Products

Methane

(reducing

agent)

Oxygen

(oxidizing

agent)

Carbon dioxide

Water

Slide 14

Oxidation of Organic Fuel Molecules During Cellular Respiration

During cellular respiration, the fuel (such as glucose) is oxidized, and O2 is reduced:

Slide 15

Fig. 9-UN3

becomes oxidized

becomes reduced

Slide 16

Fig. 9-UN4

Dehydrogenase

Slide 17

Stepwise Energy Harvest via NAD+ and the Electron Transport Chain

In cellular respiration, glucose and other organic molecules are broken down in a series of steps

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

As an electron acceptor, NAD+ functions as an oxidizing agent during cellular respiration

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

Slide 18

Fig. 9-4

Dehydrogenase

Reduction of NAD+

Oxidation of NADH

2 e– + 2 H+

2 e– + H+

NAD+

+

2[H]

NADH

+

H+

H+

Nicotinamide

(oxidized form)

Nicotinamide

(reduced form)

Slide 19

NADH passes the electrons to the electron transport chain

Unlike an uncontrolled reaction, the electron transport chain passes electrons in a series of steps instead of one explosive reaction

O2 pulls electrons down the chain in an energy-yielding tumble

The energy yielded is used to regenerate ATP

Slide 20

Fig. 9-5

Free energy, G