How Cells Make ATP
Chapter 7
Cellular Respiration

Aerobic respiration:
–
–
–

Anaerobic respiration
–
–

Releases the energy in glucose in a steady fashion
Requires molecular oxygen
Includes redox reactions
Anaerobic respiration and fermentation
Does not require oxygen
All exergonic
Aerobic respiration

1.
2.
3.
4.
Four stages:
Glycolysis – in the cytosol
Formation of acetyl CoA
Citric acid cycle
Electron transport/chemiosmosis
in mitochondria
Figure 7-2 p. 139
Glycolysis



‘sugar splitting’
Does not require oxygen
Two major phases:
–
–

Energy investment phase (endergonic)
Energy capture phase (exergonic)
Each glucose molecule is converted to 2
pyruvate molecules and 2 NADH and 2 ATP
Formation of acetyl CoA




Pyruvate molecules (from glycolysis):
1st carboxyl group is split off as CO2
Remaining 2-carbon fragment is oxidized
and e- transferred to NAD+
The oxidized 2-carbon fragment is attached
to coenzyme A  acetyl CoA
Citric acid cycle (aka Krebs Cycle):




For every glucose molecule from glycolysis,
2 acetyl groups enter
Each 2-C acetyl group combines with a 4-C
compound
2 CO2 molecules are removed from each
1 ATP, 3 NADH, 1 FADH2 per acetyl group –
the energy here will be use to synthesize
more ATP in the next phase
Figure 7-6 p. 144
Electron transport chain





A series of electron carriers in the mitochondrial
membrane
Electrons pass down in a series of redox reactions
e- lose energy as they pass along the chain
This energy allows the cell to move H+ to the
intermembrane space and create a proton gradient
(chemiosmosis)
The H+ protons can only move back into the matrix
through ATP synthase  this provides the energy for
converting ADP + Pi to ATP
Figure 7-9 p. 148
Figure 7-10 p. 149
Substrate-level
phosphorylation
Oxidative
phosphorylation
Glycolysis
Glucose
2
ATP
Figure 7-11
Page 150Pyruvate
Acetyl
coenzyme
A
2
ATP
Citric
acid
cycle
Electron transport
and
chemiosmosis
2 NADH
4–6
ATP
2 NADH
6
ATP
6 NADH
18
ATP
2 FADH2
4
ATP
32 - 34
Total ATP from
oxidative phosphorylation
ATP
Alternative pathways


Many organisms depend on nutrients other
than glucose
Products of protein and lipid catabolism enter
the same pathways as glucose
Anaerobic respiration


Electrons transferred from fuel molecules to
the electron transport chain
The final electron acceptor is an inorganic
substance such as nitrate (for the nitrogen
cycle) or sulfate
Fermentation




Also anaerobic
But does not use an electron transport chain
Electrons are transferred to an organic
molecule
This process produces either alcohol or
lactate