CELLULAR RESPIRATION REVIEW SHEET
Cellular respiration is the process by which cells acquire energy by breaking down nutrient
molecules such as sugar. The reaction is as follows:
There are four steps in Cellular Respiration and two steps in fermentation.
FERMENTATION:
1. Glycolysis
a. Is an anaerobic process (absence of oxygen)
b. Occurs outside of the mitochondria in the cytoplasm of the cell
c. Is a set of reactions whereby a 6-Carbon Glucose molecule is broken down into
2, 3 Carbon Pyruvate molecules
d. The first step in glycolysis is the addition of two phosphates, by the oxidation of
ATP to ADP +P, onto the glucose molecule
e. The addition of the phosphates “activates” the glucose molecule (the molecule
becomes “energized”)
f. A series of oxidation-reduction reactions occurs whereby the 6-Carbon sugar is
broken down into 3-Carbon sugars. The end product is two 3-Carbon pyruvate
molecules.
g. During glycolysis, 2 ATP are used and 4 ATP are produced yielding a net total of 2
ATP , 2 NADH, and 2 PYRUVATE
h. Re-cap: 1 glucose molecule yields 2 net ATP, 2 NADH and 2 PYRUVATE!!
2. With a continued absence of Oxygen, the pyruvate molecules are further broken down
into waste products via:
a. Lactic acid fermentation- lactic acid is produced as a waste product. Bacteria,
yeast and animals do this.
OR
b. Alcoholic fermentation- alcohol and CO2 are produced as waste products.
Bacteria, yeast and plants do this.
These processes are anaerobic
CELLULAR RESPIRATION:
1. Glycolysis (see above)
2. The Preparatory Reaction
a. Occurs in the mitochondrial matrix
b. Is an aerobic process (occurs with oxygen present)
c. Occurs twice per 1 glucose molecule because two pyruvates were generated
from glycolysis
d. Each of the two pyruvate molecules is broken down into a 2-Carbon (C2) acetyl
group
e. The breakdown of pyruvate occurs with the help of Coenzyme A (CoA)
f. Electrons are removed from Pyruvate, therefore pyruvate is OXIDIZED by NAD+
and CoA
g. CO2 is released into the blood and is respired out by the lungs
h. The end product from the Prep Reaction is TWO 2-Carbon Acetyl CoA molecules
3. Citric Acid Cyle/ The Krebs Cycle
a. Occurs in the mitochondrial matrix
b. Is an aerobic process (occurs with oxygen present)
c. Occurs twice per 1 glucose molecule because two Acetyl CoA molecules were
generated from the prep reaction
d. The cycle begins when each of the two Acetyl CoA molecules enters the cycle
and is broken down through a series of oxidation and reduction reactions in the
cycle.
e. The end products of the Krebs Cycle are: 2 ATP, 6 NADH and 2 FADH2 and 4 CO2
4. The Electron Transport Chain
a. Occurs in the CRISTAE of the mitochondria
b. Requires oxygen and is therefore an aerobic process
c. Begins when the 6 NADH and the 2 FADH2 give up their electrons to COMPLEX I
(NADH-Q reductase)
d. ATP is produced when ADP +P bind together with the help of the energy from
the electrons being passed from complex to complex
e. For the purposes of this course, there are 5 major complexes and molecules you
must know and you must know their functions:
i. COMPLEX I- NADH-Q reductase (initial acceptor of electrons from NADH
and FADH2)
ii. (note- there is a COMPLEX II which oxidizes FADH2 but you are not
responsible for knowing COMPLEX II)
iii. COMPLEX III- Cytochrome reductase, also known as, Cytochrome b-c
reductase- helps to build the proton gradient
f.
g.
h.
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j.
k.
l.
m.
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iv. COMPLEX IV- Cytochrome oxidase, also known as, Cytochrome c oxidasetransfers electrons to oxygen to produce water
v. Coenzyme Q- also known as ubiquinone- An enzyme that Transfers
Electrons from Complex I (and Complex II) to Complex III
vi. Cytochrome c- An electron carrier, transfers electrons from one protein
to another
vii. ATP Synthase- an enzyme that aids in the production of ATP during
CHEMIOSMOSIS.
The electron transport chain begins when electrons are passed to complex I from
NADH and FADH2.
As electrons are passed, Hydrogen ions (H+) are carried from the matrix of the
mitochondria to the inner membrane space of the mitochondria.
The electrons are shuttled to COMPLEX III by COENZYME Q
More Hydrogen ions (H+) are carried from the matrix of the mitochondria to the
inner membrane space of the mitochondria
The electrons leave COMPLEX III and are carried to COMPLEX IV by
CYTOCHROME C
More Hydrogen ions (H+) are carried from the matrix of the mitochondria to the
inner membrane space of the mitochondria
At this point a gradient is established whereby there are MORE Hydrogen ions in
the inner membrane space than in the matrix. This is a very strong gradient.
Remember, the ions will want to move from an area of high concentration (the
inner membrane space) to an area of low concentration (the matrix).
OXYGEN IS THE FINAL ACCEPTOR OF ELECTRONS IN THE ELECTRON TRANSPORT
CHAIN. IF NO OXYGEN IS PRESENT THE ELECTRON TRANSPORT CHAIN DOES
NOT FUNCTION!!
Oxygen accepts the electrons and combines with the electrons and hydrogen to
form WATER!
At the same time, hydrogen ions flow down their concentration gradient through
the ATP SYNTHASE enzyme and ATP is produced.
CHEMIOSMOSIS is the process of producing ATP molecules from the movement
of hydrogen ions through ATP Synthase.
The total end product of the Electron Transport Chain is 32-34 ATP
THE END PRODUCT OF THE ENTIRE CELLULAR RESPIRATION PROCESS IS
36-38 ATP!!