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Cellular Respiration Bio 30
During cellular respiration, living organisms break down organic molecules to obtain energy!
The overall reaction that occurs in respiration is as follows:
Recall: Organic molecules contain CARBON. ATP is a source of energy used by cells. The
energy is stored between the second and third phosphate molecules.
NOTICE: The formula for respiration is the opposite of the formula for photosynthesis!
There are three main parts to cellular respiration:
1. Glycolysis
2. The Krebs Cycle
3. Electron Transport
Glycolysis is an anaerobic process; meaning it does not require oxygen in order to take place. The
Krebs Cycle and electron transport chain both require oxygen in order to occur, thus they are
aerobic processes. An easy way to remember this is when someone exercising is doing “aerobics”,
they require oxygen in order to do that workout!
1. Glycolysis:1
“Lysis” means splitting, therefore we can predict from
the name of this process that something is getting split
or broken down. In the case of glycolysis, glucose
molecules (C6H12O6) are being broken down in the
cytoplasm of the cell. Through the breaking down of
glucose C6H12O6, two molecules of ATP are required
and FOUR molecules of ATP are produced.
Therefore the net production of ATP is 2 ATP.
Glycolysis also produces 2 molecules of NADH which
are electron carriers. Phase 1 is known as the
“investment” stage, because we use up 2 ATP
molecules to break down the Glucose into a 3-carbon
sugar called Glyceraldehyde-3-P. Phase 2 is known as
the “Energy Payoff” Stage because our investment
“pays out” and we receive 4 ATP and 2 NADH. At
the beginning of phase 2, another phosphate group is
added to Glyceraldehyde-3-P creating 1, 3
Bisphosphoglycerate, which is broken down further into 2 molecules of Pyruvate.
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Photo Taken From: http://www.hartnell.edu/tutorials/biology/cellularrespiration.html
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Cellular Respiration Bio 30
What happens to the molecules of pyruvate? Are they just waste products??? NO! The molecules
of pyruvate will move from the anerobic process of glycolysis, into the aerobic process called the
Krebs Cycle. Pyruvate is transported in the cell into the mitochondrial matrix (found in the
mitochondria). The Krebs Cycle is also known as the Citric Acid Cycle.
2. The Krebs Cycle2
Before pyruvate enters the Krebs Cycle, it reacts
with a coenzyme CoA and becomes Acetyl-CoA.
At this same time, CO2 is released and a NAD+
gains an electron and becomes NADH. CoA
then enters the Krebs Cycle and the steps are as
follows:
1. CoA combines with a 4-C compound and
forms a 6-C compound known as Citric
acid.
2. Citric acid is broken down, releasing 2
molecules of CO2 , generating 3 NADH,
1 ATP and 1 FADH2 one molecule of
NADH
3. You have now broken down your citric
acid into a 4-C compound, which will
then react with CoA and the cycle will
start all over.
REMEMBER two molecules of pyruvate are
created for every one molecule of glucose!!! So
this cycle will occur two times for everyone one
molecule of glucose.
The Net Yield (of 2 turns)
6 CO2 , 2 ATP, 8 NADH, 2 FADH2
The electron carriers, NADH and FADH2 will move on towards the electron transport chain. CO2
is exhaled, 2 ATP can be used in the cell for a quick energy supply.
Checkpoint Questions:
1. Why does the Krebs cycle turn twice for every molecule of glucose?
2. What molecule fuels cellular respiration?
3. What 3-C molecule enters the Krebs Cycle?
4. What the differences between Phase 1 and 2 in glycolysis?
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Cellular Respiration Bio 30
The electron carriers head for the…..
3. The Electron Transport Chain 3
The electron transport chain is the final process in the breakdown of glucose and is in fact, the
most profitable. The electron carriers arrive at the electron transport chain, where they release the
electron that they are carrying. However, they cannot release the electron they are carrying without
releasing a hydrogen ion H+ into the mitochondrial matrix. These hydrogen ions are very
important and are what create the power for driving ATP synthesis (the making of ATP from ADP
and P). All throughout the electron transport chain, H+ ions are pumped across the membrane
into the intermembrane space, creating a concentration gradient. This occurs because the H+
concentration in the intermembrane space will continue to increase and become greater than the
H+ concentration inside the mitochondrial matrix. These H+ ions will want to move from a high
to low concentration. ATP synthase is a huge complex made up of proteins which facilitates the
movement of H+ ions. As H+ ions move through the ATP synthase, they generate power and
synthesize ADP + P to create ATP. The electron transport chain produces 32 ATP.
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Cellular Respiration Bio 30
Final CheckPoint:
1. How many ATP are produced from one molecule of glucose?
Include the amounts of ATP generate from glycolysis, Krebs cycle
and electron transport chain.
2. What is the purpose of electron carriers?
3. What would happen to a human if their cells were unable to
generate electron carriers?
4. What is the purpose of establishing a concentration gradient in the
electron transport chain?
5. What provides the power for H+ ions to move across the
mitochondrial membrane? E- and concentration gradient.
6. Summarize how glucose is used to provide energy in respiration.
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