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Chapter 7
Aerobic cellular respiration
Anaerobic cellular respiration
Electron transport chain
Substrate level phosphorylation
Oxidative phosphorylation
ATP synthase
7.1 Overview of Respiration
Cellular respiration – oxidation of food to produce energy
Redox reactions – electrons take their energy with them (energy determined by
orbital position)
Electron carriers (NADH and FADH2)
Uses a step wise pathway to harness max amount of energy (electron transport chain)
ATP is energy
Made by
Substrate level phosphorylation (glycolysis and Kreb’s)
Oxidative phosphorylation (ETC)
7.2 Glycolysis: Splitting Glucose
Occurs in the cytoplasm
Breaks down glucose into 2 pyruvate molecules
3 things happen through glycolysis:
Priming (endergonic stage)
Cleavage (6 carbon glucose split into 2 3 carbon molecules – ultimately pyruvate)
Oxidation (which results in ATP formation during exergonic stage)
First stage is endergonic (requires energy):
Glucose is phosphorylated by ATP (glucose 6 phosphate) *This is the
phosphorylation that traps glucose inside the cell!!!
Rearranged into fructose 6 phosphate (this is a reversible isomerization)
Glucose is phosphorylated by ATP (fructose 1,6 bisphosphate)
(It costs 2 ATP to start glycolysis)
Phosphorylation provides energy necessary to make molecule reactive – push
over threshold.
Second stage is exergonic:
This second phosphorylation causes the double phosphorylated molecule to split
into 2 molecules of glyceraldehyde 3 phosphate (actually it splits into one molecule of
glyceraldehyde 3 phosphate and one molecule of dihydroxy acetone, but the dihydroxy
acetone is converted to glyceraldehyde 3 phosphate.)
Glyceraldehyde 3 phosphate is converted to an unstable intermediate and gives
one of its phosphate groups to ADP  ATP
Glyceraldehyde 3 phosphate also liberates electrons and hydrogen which are
picked up by the electron carrier NAD+  NADH
Several reactions producing intermediates
H2O is released from pathway
PEP (phospho-enol pyruvate) is converted to pyruvate when it looses a phosphate
group to ADP  ATP
This is substrate level phosphorylation – direct transfer of a phosphate from a
substrate of a reaction to another molecule (ADP in this case)
2 molecules of pyruvate
2 H2O
End products will move on
Don’t bit off more than you or your students can chew as you go through the chemistry
and the nomenclature here. At the end of the day we are looking for an overall
understanding of this pathway. Students will NOT need to know the 9 intermediates
involved, but sometimes looking at the chemistry can help them understand what’s
NAD+ must be present for glycolysis to continue. Can be regenerated by:
Aerobic respiration (oxygen will ultimately accept the electrons from NADH
returning it to NAD+)
Fermentation (organic molecules can accept electrons from NADH returning it to
Anaerobic respiration (an inorganic molecule other than oxygen will act as TEA
regenerating NAD+) I don’t know why this alternative is not mentioned in the book and I
think it confuses the issue between anaerobic respiration and fermentation for it not to be
7.3 The Oxidation of Pyruvate to Produce Acetyl-CoA
Occurs in the mitochondrion
There is a transport protein to bring pyruvate into the inner mitochondrial membrane. An
enzyme removes one C from pyruvate which is released as CO2. Acetyl Co-A is formed
for the Krebs’ cycle. Also formed is 1 NADH each (so 2 per glucose)
2 CO2
I am a fan of tracking carbons. If pyruvate has 3 and acetyl Co-A has 2 this is how we are
able to create CO2.
7.4 Kreb’s Cycle
Occurs in the mitochondrion
Cyclic pathway
Acetyl Co-A transfers two carbons to oxaloacetate forming citrate (Kreb’s is also
called the Citric Acid Cycle due to citrate being the first stable intermediate)
An isomerization produces isocitrate
An oxidation reaction produces NADH and a decarboxylation produces CO2. The
remaining intermediate is alpha-ketoglutarate.
In a similar oxidation / decarboxylation reaction succinyl-CoA is formed and
NADH and CO2 are released.
Substrate level phosphorylation produces ATP and results in succinate being left
in the cycle. You can mention the role of GTP here if you want to, but I tend to gloss over
A weaker oxidation (not associated with a decarboxylation) produces FADH2 and
The addition of water creates malate.
The oxidation of malate to regenerate oxaloacetate also produces NADH.
As the cycle turns it produces CO2, ATP, NADH, FADH2 and regenerates oxaloacetate
NET PRODUCTS (from one pyruvate
from two pyruvate):
2 CO2
4 CO2
Students do not need to know intermediates here either; but I always mention them and
show a picture of chemical structures and names. Debatably, the most important thing
generated here are the electron carriers because of the amount of energy they will be able
to produce in the ETC.
7.5 Electron Transport Chain and Chemiosmosis
Electron carriers delivered to the inner mitochondrial membrane from glycolysis and
NADH and FADH2 donate electrons which flow along the electron transport chain in the
inner mitochondrial membrane.
H are pumped out and allowed to come back in through ATP synthase producing ATP.
Spent electrons are picked up by the terminal electron acceptor (oxygen for aerobic
Oxygen also picks up hydrogen and water is produced
O2 plus the 10 NADH and 2 FADH2 from Glycolysis, Oxidation of pyruvate and Krebs
 34 ATP and 4 H2O
This is oxidative phosphorylation!!! They need to have an appreciation for this part of the
7.6 Energy Yield of Aerobic Respiration
Glycolysis 2ATP
Krebs 2 ATP
38 ATP
Energy yield can fluctuate. NADH from glycolysis can’t enter mitochondria; it must pass
its electrons to transport proteins. This costs ATP.
NADH passes electrons at a point on the chain that produces 3 ATP.
FADH2 makes only 2 ATP.
***The textbook provides a modified energy yield of 32 ATP due to alternate
calculations of ATP generated from electron carriers. It assumes NADH produces 2.5
ATP and FADH2 produces 1.5. While I have recently found some discussion on this I am
NOT inclined to teach it this way. In my opinion it is a case of researchers trying to make
the actual equal the theoretical.*** They have a hard enough time keeping up with all the
letters and numbers why add to the confusion!
7.7 Regulation of Aerobic Respiration
Cells control the rate of cellular respiration through a system of feedback inhibition
Excess ATP shuts down the pathway and stops ATP production
As ATP is used by the cell it triggers the production of more.
7.8 Oxidation Without Oxygen
Anaerobic cellular respiration uses the same pathway already described, but it does not
use oxygen as its terminal electron acceptor
Sulfur, nitrate, carbon dioxide or even inorganic metals serve as TEAs
Starts with glycolysis
Glycolysis yields 2 ATP, 2 pyruvate, 2 NADH
An organic substance formed from glucose is the TEA
Fermentation regenerates NAD+
Alcoholic fermentation:
Pyruvate is converted to acetaldehyde
Acetaldehyde accepts electrons from NADH and becomes ethanol (alcohol).
CO2 is produced
Prominent in baking and brewing industries
Baking – CO2 makes bread light and airy, ethanol evaporates away
Brew – yeast feed on sugar in grapes and produce ethanol.
Can occur in fungi, plants and bacteria, yeast
Lactate fermentation:
Pyruvate accepts electrons from NADH
This regenerates NAD+
Electron transfer converts pyruvate to lactate
Used to produce yogurt, cheese, sauerkraut, etc.
Muscles use when there is an O2 debt
Lactate can be converted back to pyruvate when O2 is available again
Occurs in animals, some fungi and some bacteria
Our muscles have slow-twitch muscle fibers for prolonged activity using
aerobic respiration. These cells are darkened due to the large numbers of myoglobin (bind
and store oxygen)
Our muscles also have fast-twitch muscle fibers for short bursts of
immediate intense use. These cells are paler and perform anaerobic fermentation when
Muscle composition is the difference between great sprinters and great
marathon runners.
7.9 Catabolism of Proteins and Fats
Nucleic Acids: nitrogenous bases converted to nitrogenous waste, carbons enter
glycolysis or Kreb’s
Proteins: amino group (nitrogen group) is removed as waste and carbon backbone goes
into glycolysis and/or Kreb’s
Fats: glycerol goes into glycolysis and carbon backbone goes into Kreb’s
7.10 Evolution of Metabolism
Carbon degradation
Anoxygenic photosynthesis
Oxygen forming photosynthesis
Nitrogen fixation
Aerobic respiration
I never have time to cover this section
This chapter is a pathway chapter. Students need to understand all the steps in the
pathway with particular interest on starting and ending molecules and what is produced
(electron carriers, ATP, CO2, etc). Be careful not to loose the forest for the trees. It is
more important that they know Kreb’s produces electron carriers for the ETC than it is
that oxaloacetate is the molecule that accepts acetyl-CoA. If you mention differences in
ATP yield you should only do so as examples of diversity. It is more important that they
know textbook yields than specializations. Students don’t need to know the molecular
mechanisms for fermentation, but should know what it is accomplishing. You don’t need
to cover evolution of metabolism.
I have also included a document on nutrition. I like to spend a day talking about alternate
energy (7.9 expanded) and how it relates to what they eat. I also like for them to bring in
food labels or to log what they eat and what’s in it a few days prior to this discussion. It
makes it more meaningful when they are looking at their list and Monster has 100
calories and 27g of sugar per 8oz and there are 24oz in the can they drank. That’s 300
calories and almost 90g of sugar! If they only need 2200 calories a day that’s 13% of
their calories in a single drink! 1 sausage egg McMuffin (sorry McDonald’s) has 450
calories and 27g of fat (that is 47% of the fat recommended for an entire day!) There are
tons of sites they can look up calorie content, but they cannot forget that serving size
doesn’t always mean what’s in the entire container. Like Coke is labeled for 8oz knowing
there are 12oz in a can!