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Lecture 30 – Lecture 31
Cellular Respiration
Ozgur Unal
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How do most autotrophs produce food?
Can anyone predict how heterotrophs obtain energy?
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What is respiration?
Cellular respiration is the catabolic pathway in which
organic molecules are broken down to release energy for use
by the cell.
In cellular respiration, O2 is used to break down organic
molecules, resulting in the production of CO2 and water.
C6H12O6 + 6O2 ---------------> 6CO2 + 6H2O + energy
Opposite of photosynthesis!
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Cellular respiration occurs in two main parts: Glycolysis and
Aerobic respiration.
Glycolysis is an anaerobic process.
Anaerobic processes do not require oxygen.
Aerobic respiration is an aerobic process and it includes
Krebs cycle and electron transport.
Aerobic processes require oxygen.
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Glucose is broken down in the
cytoplasm through the process of
glycolysis.
Two molecules of ATP and two
molecules of NADH are produced
for each molecule of glucose.
Follow Figure 8.12 as you read the
text.
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Most of the energy from the glucose is still contained in the
pyruvate.
Pyruvate is transported to mitochondria where it is broken
down into CO2 by a process called Krebs Cycle, aka TCA
cycle or Citric acid cycle.
Follow the steps of the Krebs cycle in
Figure 8.13.
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In aerobic respiration, electron transport is the final step in
the breakdown of glucose.
Most of the ATP is
produced in this process.
Follow Figure 8.14 for the
details of the electron
transport.
In eukaryotic cells 1 glucose yields 36 ATP.
In prokaryotic cells 1 glucose yields 38 ATP.
This difference is due to the fact that prokaryotes do not
spend energy to transport pyruvate to a mitochondrion
because they do not have mitochondria.
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If you drink a soft drink containing
33 grams of sugar (sucrose) why don’t
you gain the weight of the sugar?
The body will store only a fraction of the 33 grams, while
breaking down the rest. The sugar will be broken down to
ultimately form CO2 by aerobic respiration. The H atoms
found in the sucrose molecules will unite with O gas to
produce H2O. Most of the water produced will be eliminated
by breathing and urination. However, some sugar wil be
retained in the cell. If the sugar is not needed for cellular
respiration, it will be converted to glycogen or lipids for
storage.
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Some cells can function for a short time when O2 levels are
low.
Some prokaryotes are anaerobic organisms: They grow and
reproduce without O2.
These cells continue to produce ATP through glycolysis.
However, when NAD+ supply finishes, glycolysis cannot
continue.
In order to regenerate the supply of NAD+, cells do
anaerobic respiration, also called fermentation.
There are two main types of fermentation: Lactic Acid
Fermentation and Alcohol Fermentation.
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In lactic acid fermentation, cells
convert pyruvate produced in
glycolysis into lactic acid.
This process produces NAD+.
Skeletal muscle cells produce lactic acid when the body
cannot supply enough O2.
When lactic acid builds up in the muscle, muscles become
fatigued and might feel sore.
Other examples: Production of some food such as cheese
and yoghurt.
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In alcohol fermentation, pyruvate is converted into ethyl
alcohol and CO2.
Similar to lactic acid fermentation, this process produces
NAD+.
Example: Production of wine.
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