Download Glycolysis and Cellular Respiration


A key energy-storing molecule:
 Nearly all cells metabolize glucose
for energy
 Other organic molecules are
converted to glucose for energy
harvesting
C6H12O6 + 6O2  6CO2 + 6H2O + ATP + (heat E)

The main stages of glucose metabolism are:

Glycolysis

Cellular respiration

Glycolysis

Occurs in cytosol

Does not require oxygen

Breaks glucose into pyruvate

Yields two molecules of ATP per molecule of
glucose


If oxygen is absent fermentation occurs
 pyruvate is converted into either lactate,
or into ethanol and CO2
If oxygen is present, cellular respiration
occurs

Occurs in mitochondria (in eukaryotes)
 In cytosol (in prokaryotes)

Requires oxygen

Breaks down pyruvate into carbon dioxide
and water

Produces an additional 32 or 34 ATP
molecules, depending on the cell type

Each molecule of glucose is broken down
to 2 molecules of pyruvate.

A net of 2 ATP and 2 NADH molecules
are formed.




Occurs under anaerobic conditions
Pyruvate is converted into lactate or ethanol and
CO2
Fermentation does not directly produce more
ATP
But is necessary to regenerate NAD+, which
must be available for glycolysis to continue


Some cells ferment
pyruvate to form acids
Human muscle cells can
perform fermentation

Anaerobic conditions
produced when muscles
use up O2 faster than it
can be delivered (e.g.
while sprinting)

Lactate (lactic acid)
produced from pyruvate


Some microbes ferment pyruvate to other acids
(as seen in making of cheese, yogurt, sour cream)
Some microbes perform fermentation exclusively
(instead of aerobic respiration)
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

Yeast cells perform
alcoholic fermentation
Glucose is fermented to
ethanol and CO2

Occurs within
mitochondria in
eukaryotic cells

Most of energy in glucose is stored in electron
carriers NADH and FADH2



Only 4 total ATP produced per glucose after complete
breakdown in the Krebs Cycle
NADH and FADH2 deposit electrons into electron
transport chains in the inner mitochondrial
membrane
Electrons join with oxygen gas and hydrogen ions
to make H2O at the end of the ETCs
1. Energy released from electrons as they are passed
down the ETC
2. Released energy used to pump H+ across inner
membrane
 H+ accumulate in intermembrane space
3. H+ form a concentration gradient across the
membrane (a form of stored energy)
4. H+ flow back into the matrix through an ATP
synthesizing enzyme


Flow of H+ provides energy to link 32-34
molecules of ADP with phosphate, forming 3234 ATP
ATP then diffuses out of mitochondrion and
used for energy-requiring activities in the cell


Metabolic processes in cells are heavily
dependent on ATP generation
Muscle cells switch between fermentation and
aerobic cell respiration depending on O2
availability
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