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The Basics of Cellular
Respiration (CP)
Cell respiration:
The process of breaking down “food”
(glucose molecules) in the presence of
oxygen, ATP molecules (cell energy
molecules) are produced.
Much of it happens in the mitochondria.
Cell Respiration: Overall Equation
•
1 gram of Glucose, when burned in
the presence of oxygen, releases
3.811kcal of heat energy.
•
When the end phosphate group is released
from ATP, .007 kcal is available for work.
(1 calorie = amount of heat needed to raise temp.1o C.
1Calorie (Food Calorie) = 1 kilocalorie or 1000 calories)
Cells don’t “burn” glucose as rapidly as
combustion, but, instead gradually release
its energy.
The cell cannot use the amount of energy in
a glucose molecule all at once.
The cell uses energy in the smaller “packets”
contained in ATP molecules.
Both plant & animal cells must
use cell respiration in order to
provide the ATP molecules they
need.
Cell respiration also provides
“carbon skeletons” used in
formation of other organic
compounds.
Cellular respiration may be
thought of as 3 major processes
• 1) Glycolysis – anerobic process (no O2)
listed separately in CP Bio Text
• 2) Krebs cycle – aerobic process (uses O2)
also called “Citric Acid Cycle”
• 3) Electron Transport System (chain) aerobic (Oxidative phosphorylation)
or E.T.O.P.)
Part I - Glycolysis
One molecule of glucose (6 carbons)
is converted into two 3 carbon
pyruvic acid molecules.
• Glycolysis occurs in the
cytosol of the cytoplasm and
is considered anaerobic
because no oxygen is required
during this process.
2 ATP molecules needed to start the
process.
4 ATP are actually produced,
2 ATP = net gain
(Although the yield is small, the cell can use this process
to produce thousands of ATPs in milliseconds.)
Part II- Krebs cycle (Citric Acid Cycle)
It is named for Hans Krebs who
discovered it in 1953. (It is also called
the citric acid cycle” because citric
acid is formed at the start of the
cycle.)
1) Pyruvic acid (from glycolysis)
is converted to Acetyl “CoA”
which is broken down into carbon
dioxide (CO2) in a series of
energy-extracting reactions.
2) It is an aerobic process (requires O2)
& is located in the mitochondrion. The
inner folds called cristae increases the
surface area for chemical reactions
involved in cell respiration.(more ATPS made)
3) For each 3-carbon pyruvic acid,
1 ATP is produced. Therefore a
total of 2 ATPs are produced
from one glucose.
4) Protons (H+ ions) and electrons are
carried by special compounds (NADH &
FADH2) from Krebs Cycle for use in the
Electron Transport Chain.
CO2 is given off from Krebs cycle.
III) The Electron Transport System
(chain) (Let’s call it E.T.) & Oxidative
Phosphorylation.
E.T. provides energy to produce
the most ATPs of cell respiration
1) Takes place within the
mitochondria.
2) Electrons are carried & ATPs are
produced: High energy electrons
from Krebs cycle are passed from
one “electron carrier” to the next.
• Electrons are passed from one carrier
(cytochrome proteins) to the next in E.T.
Modern Biology (Holt)
Energy given off from this process permits ATP
synthase located on the inner membrane to
produce ATPs.
3) One glucose molecule is responsible for the
gain of 34 ATP molecules from E.T.
4) Oxygen is the final electron acceptor in the
chain. The O2, electrons are combined with
hydrogen ions to produce H2O.
• Due to the proton concentration gradient produced, the
protons diffuse back across the membrane to the matrix,
through ATP synthase enzyme complex.
• This is called chemiosmosis.
• It produces 34 ATPs.
Modern Biology (Holt)
ATP Final Tally from 1 glucose broken
down through cell respiration.
• Glycolysis
= 2 ATPs
• Krebs Cycle (Citric Acid Cycle) = 2 ATPs
• Electron Transport System & Oxidative
Phosphorylation (E.T.O.P.)
= 34 ATPs
Total =
38 ATPs