1. Anaerobic Respiration
How cells make ATP in the
absence of oxygen

2. Fermentation Allows Cells to
Make ATP Without Using Oxygen
Glucose
Glycolysis
Oxygen Present
Citric Acid Cycle
Oxidative Phosphorylation
Oxygen Absent
Fermentation
Alcohol
Lactic
Acid

3. Remember…
 Glycolysis happens in
the cytosol
 It does not require the
presence of oxygen
 NAD+ acts as the
electron acceptor
 2 ATP are generated
 2 NADH are
generated

5. Fermentation
 An extension of glycolysis
 Cells can use this step of respiration to
keep up the ATP supply
 But…must have a steady supply of
NAD+ to act as the electron acceptor

6. •Unlike aerobic respiration, fermentation generates ATP
through substrate-level phosphorylation
•Fermentation can only continue if there’s a supply of the
oxidizing agent NAD+ to be used in glycolysis
After NADH is
produced from
glycolysis,
its electrons are
transferred to
pyruvate.
This regenerates the
NAD+ that can again
be used for another
round of glycolysis.

9. In contrast…
 In aerobic respiration the supply of NAD+ is
continually renewed as
the NADH molecules
deliver their electrons to
the electron transport
chain

10. Fermentation
 In anaerobic
respiration, we need
another way to recycle
NAD+
 Instead, the electrons
in NADH are
transferred to
pyruvate, the end
product of glycolysis

11. LE 9-18
Glucose
CYTOSOL
Pyruvate
No O2 present
Fermentation
O2 present
Cellular respiration
MITOCHONDRION
Ethanol
or
lactate
Acetyl CoA
Citric
acid
cycle

12. So fermentation is…
 Glycolysis (2 ATP, 2 NADH, pyruvate)
PLUS
 Extra reactions that oxidize the NADH to
NAD+ by transferring electrons to
pyruvate

13. 2 main types of fermentation
 Alcohol fermentation
 Lactic acid fermentation

14. There Are 2 Types of Fermentation
Alcohol Fermentation
•Glycolysis makes
pyruvate
•CO2 is released from
pyruvate.

15. Alcohol
fermentation
 Occurs in yeast and many bacteria
 Pyruvate (3 carbons) converted to
acetaldehyde (2 carbons) and CO2 is released
(used in baking to make bread rise)
 Acetaldehyde is reduced by NADH to ethanol,
thus regenerating the supply of NAD+

16. Lactic Acid Fermentation
 Occurs in muscle cells, some bacteria,
some fungi
 Pyruvate is reduced by NADH to lactic acid,
thus regenerating the supply of NAD+

17. Muscle Cells
 When muscles are working
hard, they quickly exhaust the
supply of oxygen to the cell
 The cell launches into
fermentation to keep up
 Lactic acid accumulates in
cells leading to cramps

18. Facultative Anaerobes
 Organisms that can survive using either
anaerobic or aerobic respiration
 Yeast
 Bacteria

19. Main differences between aerobic
and anaerobic respiration
 Aerobic
Final electron
acceptor - oxygen
NAD+ regenerated
when electrons
delivered to ETC
Huge energy payoff 38 ATP, glucose fully
broken down through
Citric Acid cycle
 Anaerobic
Final electron
acceptor - pyruvate or
acetaldehyde
NAD+ regenerated
when electrons given to
pyruvate or
acetaldehyde
Less energy payoff 2 ATP, energy still
trapped in pyruvate or
ethanol

20. Ancient prokaryotes probably used
glycolysis to make ATP
What is the basis for this statement??
•The oldest prokaryotes were around before there was
sufficient oxygen in the atmosphere
•Glycolysis is the most widespread metabolic pathway
among organisms
•Glycolysis occurs in the cytosol…..prokaryotes don’t
have organelles

21. Glycolysis and the Citric
Acid Cycle Connect to
Many Other Metabolic
Pathways
Many molecules aside from
glucose can be used in
cellular respiration to make
ATP:
The monomers of different
molecules begin the
process at different steps

22. The energy in
organic
molecules, which
is used to power
the cell, is
released, but not
produced during
cellular
respiration.