The Kreb’s Cycle
and Electron
Transport Chain
Biology 112
The End of Glycolysis
 Only
10% of the energy available in
glucose has been used
 The rest is still contained in pyruvic acid
 The remainder of the energy needs
oxygen for the final phases of cellular
respiration

These pathways are said to be aerobic
The Kreb Cycle
 Steps





of this process:
Pyruvic acid enters the mitochondrion
One of the three carbons becomes part of
a carbon dioxide molecule
The remaining two carbon molecules
attach to a coenzyme and form citric acid
The citric acid breaks down, releasing more
carbon dioxide
Energy is released in the form of NADH
The Kreb’s Cycle - cont
 Citric
acid turns into a five carbon
molecule which then releases another
carbon atom to form more carbon
dioxide
 NADH and ATP is also released
 The four carbon molecule remaining will
be picked up and used again in the cycle

NADH and FADH2 (another energy releasing
molecule) is released
The Electron Transport Chain
 NADH
and FADH2 enter the electron
transport chain to be used to generate
ATP from ADP
 It is composed of carrier proteins
embedded in the mitochondria
(eukaryotes) or cell membrane
(prokaryotes)
 The end of the chain releases water
Adding Up the ATP
 By
the end of cellular respiration – 36 ATP
molecules will have been produced from
one molecule of glucose
 The cell can generate energy from more
than just glucose
 Any energy not used by the cell is
released as heat
Quick and Long Term Energy
 Overall,
a small amount of ATP is
produced by cellular respiration
 After a few moments of intense activity,
for instance, lactic acid fermentation
produces necessary ATP for energy
 Lactic acid will require oxygen in order to
be broken down
 The body stores more energy in the form
of the carbohydrate glycogen
 After this is used, fats and other molecules
are utilized
Photosynthesis vs. Respiration
Photosynthesis
Respiration
Function
Requires energy
Releases energy
Location
Chloroplasts
Mitochondria
Reactants
CO2 + H2O
C6H12O6 + O2
Products
C6H12O6 + O2
CO2 + H2O