Cellular Respiration
Mrs. Schenfield’s
Life Science
Cellular Respiration Overview
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Transformation of chemical energy in food into
chemical energy cells can use: ATP
These reactions proceed the same way in plants
and animals. Process is called cellular
respiration
Overall Reaction:
–
C6H12O6 + 6O2 → 6CO2 + 6H2O
Anaerobes
 Anaerobes
are organisms that
use the Anaerobic Respiration
pathway
 Most anaerobes are bacteria
(not all).
 Anaerobes do NOT require
oxygen.
Aerobes
 Aerobes
are organisms that
use the Aerobic Respiration
pathway.
 Aerobes require oxygen.
Cellular Respiration Overview
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Breakdown of glucose begins in the cytoplasm:
the liquid part called cytosol
Sugar is the most common energy source (some
cells use fats and proteins)
Requires many enzymes
The enzymes “disassembly line” takes the sugar
apart, periodically releasing small amounts of
energy that fuel the cell
Types of Cellular Respiration

At this point life diverges into two forms and two
pathways
– Anaerobic
cellular respiration
(fermentation)
– Aerobic cellular respiration
Cellular Respiration Reactions

Glycolysis
Series of reactions which break the 6-carbon glucose
molecule down into two 3-carbon molecules called
pyruvate
-all organisms from simple bacteria to humans
perform it the same way
– Yields 2 ATP molecules for every one glucose
molecule broken down
–
Glycolysis
 glyco
means “glucose/sugar”, and
 lysis means “to split”. Therefore,
 glycolysis means “to split
glucose”

This process was likely used to supply
energy for the ancient forms of bacteria.
Anaerobic Cellular Respiration

Some organisms thrive in environments with little or no
oxygen
–
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Marshes, bogs, gut of animals, sewage treatment ponds
No oxygen used= ‘an’aerobic
Results in no more ATP, final steps in these pathways
serve ONLY to regenerate NAD+ so it can return to pick
up more electrons and hydrogens in glycolysis.
End products such as ethanol and CO2 (single cell fungi
(yeast) in beer/bread) or lactic acid (muscle cells)
Anaerobic Cellular Respiration
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Alcoholic Fermentation-some bacteria and fungi use
this as their only source of energy.
Yeast in bread dough uses this and produces carbon
dioxide that gets trapped in the dough and causes
bread to rise.
Yeast is a leavening agent and is mentioned in the
Bible.
(enzymes)
Sugar

carbon dioxide + 2 ATP
Alcoholic Fermentation
 Uses
only Glycolysis.
 Does NOT require O2
 Produces ATP when O2 is
not available.
Alcoholic Fermentation
(Ethyl Alcohol or
Ethanol)
C6H12O6
2 C2H5OH + 2 CO2
As a result of Alcoholic Fermentation,
Glucose is converted into 2 molecules of
Ethyl Alcohol and 2 Molecules of Carbon
Dioxide.
Anaerobic Cellular Respiration
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Lactic Acid Fermentation-produced and released
by bacteria in yogurt, buttermilk, and sauerkraut.
If, when you exercise, you are not able to supply
enough oxygen to muscle cells they will switch to
anaerobic respiration which produces lactic acid.
The build up of lactic acid causes soreness in
muscles.
Not as efficient as aerobic cellular respiration
Lactic Acid Fermentation
 Uses
only Glycolysis.
 Does NOT require O2
 Produces ATP when O2 is
not available.
Aerobic Cellular Respiration


Oxygen required=aerobic
Mitochondria perform the “recharging” of ATP
molecules by transferring energy from the sugar
molecules to ATP.
(enzymes)
Sugar + oxygen

 carbon dioxide + water + 36 ATP
The cells of many organisms and your body perform this
type of cellular respiration.
In order for Aerobic
Respiration to continue
the Pyruvic acid is first
converted to Acetic
Acid by losing a carbon
atom and 2 oxygens as
CO2.
The Acetic acid then
must enter the matrix
region of the
mitochondria. The CO2
produced is the CO2
animals exhale when
they breathe.
Phase Two: The Krebs Cycle
(AKA the Citric Acid Cycle)
Once the Acetic Acid enters the Matrix it combines with
Coenzyme A to form a new molecule called Acetyl-CoA. The
Acetyl-CoA then enters the Krebs Cycle.
Sir Hans Adolf
Krebs
Produces most of the
cell's energy in the
form of NADH and
FADH2… not ATP
Does NOT require O2
CoA breaks off to gather more
acetic acid. The Acetic acid is
broken down.
+ 3H
3 NADH
Energy Tally
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36 ATP for aerobic vs. 2 ATP for anaerobic
–
Glycolysis
2 ATP
–
Kreb’s (citric acid cycle)
2 ATP
–
Electron Transport
32 ATP
36 ATP
Anaerobic organisms can’t be too energetic but
are important for global recycling of carbon