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Cellular Respiration
•The second stage of cellular respiration is the
Krebs cycle, which operates only when oxygen
is available.
•Because it depends on oxygen, it is an aerobic
process.
•It is named after its discoverer Hans Krebs.
•The Krebs cycle takes place in the innermost
compartment of the mitochondrion called the
matrix
Mitochondrion
Hans Krebs
Discovered “Krebs” cycle in 1937
Won Nobel Prize in 1953
Cellular Respiration
•Pyruvic acid molecules, produced by
glycolysis, enters the matrix and are broken
down through chemical reactions resulting in the
production of citric acid.
•Because this is the first product made, it is also
called the Citric Acid Cycle.
•Along with the production of citric acid, it also
releases carbon dioxide (CO2).
Cellular Respiration
•During the cycle, energy is released by the
breaking and rearranging of carbon bonds and is
captured in ATP, NADH, and FADH2.
•Once the Krebs cycle is complete, the cell goes
on to derive the majority of its ATP from the
electron transport chain.
Cellular Respiration: Krebs cycle
Steps in Cellular Location
Respiration
What goes in
What comes
out
ATP Results
(1) Glycolysis
Anaerobic
process
Cytoplasm
(cytosol)
one Glucose
2 ATP to start
2 pyruvic acids
2 NADH
4 produced for a
net gain of 2
ATP
(2) Krebs cycle
(Citric Acid
cycle)
Aerobic
process
Mitochondrial 2 pyruvic acids
Matrix
C02, 4 NADH,
2 FADH2
2 ATP
Water
NAD+
(recycled)
FAD+
(recycled)
32-34 ATP
(3) Electron
Inner
NADH,
Transport Chain Mitochondrial FADH2,
Membrane
oxygen
(cristae)
Total
36-38 ATP
Cellular Respiration
Electron Transport Chain
• The electron carriers produced during
glycolysis (NADH) and the Krebs cycle
(NADH and FADH2) bring high-energy
electrons to the electron transport chain.
• The passing of electrons through the
electron transport chain causes H+ ions to
build up in the intermembrane space,
making it positively charged relative to the
matrix.
Cellular Respiration
Electron Transport Chain
• The charge difference across the membrane
forces H+ ions through channels in enzymes
known as ATP synthases. As the ATP
synthases spin, a phosphate group is added
to ADP, generating ATP.
• At the end of the chain the electrons are
taken up by oxygen molecules, along with
hydrogen atoms, to make water.
• This is why oxygen is known as the final
electron acceptor.
Cellular Respiration
•
•
•
•
Electron Transport Chain
The electron transport chain is the stepwise
process of cellular respiration that is
responsible for producing:
Water (with the help of oxygen we breathe)
32 to 34 ATP (thanks to the proton, H+ ,
gradient)
NAD+ and FAD+ (which are recycled to be
used again in the Krebs cycle and
glycolysis)
Cellular Respiration
Electron Transport Chain
• This process happens in the mitochondria
along the inner membrane called the cristae.
Cellular Respiration
Electron Transport Chain
• To put things in perspective think about how
we breathe in oxygen with our lungs,
transport it with red blood cells in our
arteries to cells, and the oxygen is ultimately
used inside the mitochondria of every cell to
accept electrons at the end of the electron
transport chain.
Cellular Respiration
Electron Transport Chain
• For Prokaryotes, which don’t have
mitochondria, this process happens in the
cell membrane.
Cellular Respiration: Electron
Transport
Cellular Respiration
Cellular Respiration
Fermentation
•Fermentation is an anaerobic process that
converts NADH back to NAD+, thus
producing energy.
Eukaryotic cells
(1) Lactic Acid Fermentation
•Lactic acid is produced in muscles during
rapid exercise.
•This is because the body cannot supply
enough oxygen to the tissues to produce the
needed ATP.
Fermentation
•A buildup of lactic acid causes a burning
sensation in the muscles.
(2) Alcoholic fermentation
•It occurs in yeast.
•It produces alcohol and carbon dioxide(CO2).
•The CO2 is what causes dough to rise, air
spaces in bread, and bubbles in alcoholic
drinks.
Fermentation
Prokaryotic cells
•Some types of bacteria produce alcohol and
CO2.
•Other kinds of bacteria produce lactic acid.
Fermentation