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Chapter 9

Organisms need to obtain materials and
energy in order to complete necessary
reactions for life.
◦ 2 Processes
 Cellular Respiration (heterotrophs)
 glucose + O2 ---> CO2 + H20 + ATP (heat)
 Photosynthesis (autotrophs)
 CO2 + H20 (light) ----> glucose + O2

ATP (adenosine triphosphate)
◦ bonds broken via hydrolysis (release energy)
◦ molecule that provides energy to drive
cellular work
 happens via phosphorylation (adding or
removing P from ATP)
 ATP <--> ADP
 Producing ATP requires energy

Oxidation-Reduction Reactions (redox)
◦ oxidation (losing electrons)
 reducing agent (electron donor)
◦ reduction (gaining electrons--reduce positive
charge)
 oxidizing agent (electron acceptor)

Redox in Cellular Respiration...
◦ glucose oxidized to CO2
◦ oxygen reduced to H2O
◦ coenzymes are used throughout this
process to “help shuttle” the electrons (H+)
 NAD+ (nicotinamide adenine
dinucleotide)--NADH is reduced state
 FAD (flavin adenine dinucleotide)-FADH2 is reduced state

Cellular Respiration does not oxidize glucose in a single
explosive step. Instead a series of steps are used to release
small amounts of energy.
◦ Glycolysis
 in the cytosol. Glucose broken to pyruvate. Some ATP
produced.
◦ TCA (Krebs) Cycle and Pyruvate oxidation
 pyruvate further oxidized and completely broken down to
CO2 in the mitochondria. Some ATP produced.
◦ Electron Transport Chain (oxidative phosphorylation and
chemiosmosis)
 accepts electrons from carriers (NADH and FADH2) and
releases energy. ATP and H20 are produced here.

Through a series of 10 reactions, the 6-carbon sugar
(glucose), is broken down into…
◦ two molecules of a 3-carbon molecule called pyruvate
◦ net gain of 2 ATP molecules and 2 NADH molecules occurs
(inefficient)

Anaerobic process. Does not require oxygen.
Pyruvate travels into
the mitochondria via
a transport protein.


Pyruvate then gets oxidized into Acetyl-CoA
inside the mitochondria (one is produced per
pyruvate molecule)
◦ A CO2 molecule is released
◦ One NADH molecule is produced
◦ Acetyl-CoA then enters the TCA (Krebs) cycle in the
mitochondrial matrix

Begins with one Acetyl-CoA molecule
(requries two turns to completely oxidize
glucose)
◦ Produces:




2
3
1
1
CO2
NADH
FADH2
ATP
 For each Acetyl-CoA molecule

Occurs in the inner membrane of the
mitochondria (cristae—folds)
◦ Oxidative Phosphorylation
 Within the membrane are transmembrane proteins to
pump H+ ions across (creates gradient)
 Electron carriers (NADH and FADH2) donate electrons to
drive the passage of H+ ions
 Last protein oxidizes oxygen into water
◦ Chemiosmosis
 At the end of the chain, H+ passes back through the
membrane in ATP synthase, which uses the energy from
this process to convert ADP back to ATP.
 H+ gradient across a membrane used to drive cellular
work (movement of H+ ions)


Without oxygen pyruvate cannot enter the
mitochondria and begin the Krebs Cycle, oxygen is
not present to pull electrons down chain, and the
process stops.
Instead pyruvate enters into an alternate pathway
to oxidize glucose and generate ATP…
◦ Lactic acid fermentation (pyruvate to lactate)
 Regenerates NAD+ for glycolysis
◦ Alcohol fermentation (pyruvate to ethanol)
 Regenerates NAD+ for glycolysis





aerobic respiration: cell respiration that
requires oxygen (most organisms)
anaerobic respiration (fermentation): cell
respiration that occurs without oxygen
oxidative phosphorylation: ATP synthesis
powered by redox reactions in ETC (90% of
ATP generated by CR)
substrate level phosphorylation: ATP
formed by glycolysis and TCA cycle
chemiosmosis: H+ ions move through a
membrane to drive cellular work