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Cell Respiration
Cellular Respiration
• Cells must extract energy from organic molecules to
provide energy for the processes of life.
• Main source of such chemical energy are
carbohydrates, especially glucose C6H12O6.
• Cell respiration’s general formula is as follows:
Types of Respiration
•
Cellular respiration has 2 general
Classifications:
1. Aerobic Respiration occurs in the
presence of O2.
2. Anaerobic Respiration occurs in the
absence of O2.
Aerobic Respiration
Aerobic Respiration occurs in 3 steps
1. Glycolysis - The splitting of
glucose into 2 3-Carbon molecules
2. Krebs Cycle (or citric acid cycle)
3. Electron Transport
Glycolysis
•Glucose molecule is split into 2
molecules of PGAL by addition of
energy from 2 molecules of ATP
(remember ATP  ADP releases
energy)
•Each PGAL molecule is changed
by enzymes into 2 molecules of
Pyruvic Acid (a 3 carbon
molecule). This creates 1 NADH
(an energy molecule like NADPH
from photosynthesis), and 2 ATP
molecules for each pyruvic acid,
for a total of 2 NADH, and 4 ATP
molecules.
Anaerobic Respiration
• Occurs in low Oxygen situations.
• Far less efficient than aerobic respiration only yields 2 ATP per glucose molecule
• Two types:
– Lactic acid fermentation
– Alcoholic fermentation
Lactic Acid Fermentation
• Occurs in human muscle tissue - causes pain under high
exertion
• Allows recharging of NADH to NAD+ so glycolysis can
continue
• Follows following formula:
– Puruvic Acid + NADH  NAD+ + Lactic Acid
Alcoholic Fermentation
• Is widely used
commercially to
produce alcoholic
beverages
• Allows recharging
of NADH to NAD+
so glycolysis can
continue
• Follows following
formula:
• Puruvic Acid +
NADH  NAD+ +
Alcohol + CO2
Krebs Cycle
Occurs only in the presence of
oxygen.
Cycle is composed of nine steps,
which is summarized as follows:
Pyruvic acid releases a CO2 and
joins a 4C molecule to form a 6C
molecule of citric acid
The citric acid releases 2 CO2
molecules to form 2 molecules of
NADH from NAD+
The resultant 4C molecule creates 1
GTP from GDP (This will be
converted to ATP later)
The resultant 4C molecule creates 1
FADH2 from FAD+ (This will be
converted to ATP later)
Another molecule of NADH is formed
from NAD+. The resultant 4C
molecule reenters the cycle, and the
process begins again.
Electron
Transport
Cell must convert FADH2 and
NADH to ATP
22 ATP molecules are produced
through electron transport
This occurs in a process similar to
photosynthesis
NADH & FADH2 deliver H+ ions
(and electrons) to intermembrane space of
mitochondria.
As H+ concentration gradient
increases in inter-membrane
space. H+ ions diffuse back
into matrix through a special
protein called ATP synthetase.
This enzyme uses this
diffusion energy to generate
ATP.
Electrons are passed through
several membrane proteins
where they bind with 2 H+ ions
and Oxygen to form a
molecule of H2O. Thus, in
aerobic respiration Oxygen is
the final electron acceptor.
Energy Totals
Source
Number ATP Produced
Glycolysis
2 ATP
Transport of NADH into
Matrix.
-2 ATP
Krebs Cycle (ATP & GTP)
2 ATP
Electron Transport (NADH &
FADH2)
34 ATP
NET TOTAL
36 ATP
Energy Totals contd.