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Cellular Respiration
All M
C6H12O6 + 6O2 -----> 6CO2 + 6H20
+ energy (heat and ATP)
Energy
• Capacity to move or change matter
• Forms of energy are important to life include
Chemical, radiant (heat & light), mechanical,
and electrical
• Energy can be transformed from one form to
another
• Chemical energy is the energy contained in the
chemical bonds of molecules
• Radiant energy travels in waves and is
sometimes called electromagnetic energy. An
example is visible light
• Photosynthesis converts light energy to
chemical energy
• Energy that is stored is called potential energy
Laws of Thermodynamics
• 1st law- Energy cannot be created or
destroyed.
Energy can be converted from
one form to another. The sum of the energy
before the conversion is equal to the sum of
the energy after the conversion.
• 2nd law- Some usable energy is lost during
transformations.
During changes from one
form of energy to another, some usable
energy is lost, usually as heat. The amount
of usable energy therefore decreases.
Adenosine triphosphate (ATP)
• Energy carrying molecule used by cells to fuel
their cellular processes
• ATP is composed of an adenine base, ribose
sugar, & 3 phosphate (PO4) groups
• The PO4 bonds are high-energy bonds that
require energy to be made & release energy
when broken
• ATP is made & used continuously by cells
• Every minute all of an organism's ATP is
recycled
• Phosphorylation refers to the chemical reactions
that make ATP by adding Pi to ADP ADP
+ Pi
+ energy « ATP + H2O
• Enzymes
(ATP synthetase& ATPase) help
break & reform these high energy PO4 bonds
in a process called substrate-level
phosphorylation
• When the high-energy phosphate bond is
broken, it releases energy, a free
phosphate group, & adenosine diphosphate
(ADP)
Enzymes in Metabolic Pathways:
• Biological catalysts
• Speeds up chemical reactions
• Lowers the amount of activation energy needed
by weakening existing bonds in substrates
• Highly specific protein molecules
• Have an area called the active site where
substrates temporarily join
• Form an enzyme-substrate complex to stress
bonds
• Enzyme usable
• enzyme substrate
complex
Energy Carriers During Respiration:
NADH: A second energy carrying molecule in
the mitochondria; produces 3 ATP
FADH2: A
third energy carrying molecule in
the mitochondria; produces 2 ATP
Mitochondria:
• Has outer smooth, outer membrane & folded
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inner membrane
Folds are called cristae
Space inside cristae is called the matrix &
contains DNA & ribosomes
Site of aerobic respiration
Krebs cycle takes place in matrix
Electron Transport Chain takes place in
cristae
Cellular Respiration Overview:
C6H12O6 + 6O2 -----> 6CO2 + 6H20 +
energy (heat and ATP)
• Controlled release of energy from organic
molecules (most often glucose)
• Glucose is oxidized (loses e-) & oxygen is
reduced (gains e-)
• The carbon atoms of glucose (C6H12O6) are
released as CO2
• Generates ATP (adenosine triphosphate)
• The energy in one glucose molecule may be
used to produce 36 ATP
• Involves a series of 3 reactions --- Glycolysis,
Kreb's Cycle, & Electron Transport Chain
Glycolysis:
• Occurs in the cytoplasm
• Summary of the steps of Glycolysis: a. 2 ATP
added to glucose (6C) to energize it.
b.
Glucose split to 2 PGAL (3C). (PGAL =
phosphoglyceraldehyde)
c. H+ and e- (e= electron) taken from each PGAL & given
to make 2 NADH.
d. NADH is energy
and e- carrier.
e. Each PGAL rearranged
into pyruvate (3C), with energy
transferred to make 4 ATP (substrate
phosphorylation).
f. Although glycolysis
makes 4 ATP, the net ATP production by
this step is 2 ATP (because 2 ATP were
used to start glycolysis). The 2 net ATP
are available for cell use.
g. If oxygen is
available to the cell, the pyruvate will
move into the mitochondria & aerobic
respiration will
begin.
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Net Yield from Glycolysis
• 4 NADH2
• 2 CO2
• 4 ATP ( 2 used to start reaction)
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h. If no oxygen is available to the cell
(anaerobic), the pyruvate will be fermented by
addition of 2 H from the NADH (to alcohol +
CO2 in yeast or lactic acid in muscle cells). This
changes NADH back to NAD+ so it is available
for step c above. This keeps glycolysis going!
Alcoholic Fermentation
Lactic Acid Fermentation
Aerobic Respiration:
• Occurs in the mitochondria
• Includes the Krebs Cycle & the Electron
Transport Chain
• Pyruvic acid from glycolysis diffuses into
matrix of mitochondria & reacts with
coenzyme A to for acetyl-CoA (2-carbon
compound)
• CO2 and NADH are also produced
Kreb's Cycle:
• Named for biochemist Hans Krebs
• Metabolic pathway that indirectly requires O2
• Kreb's Cycle is also known as the Citric acid
Cycle
• Requires 2 cycles to metabolize glucose
• Acetyl Co-A (2C) enters the Kreb's Cycle &
joins with Oxaloacetic Acid (4C) to make
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Citric Acid (6C)
Citric acid is oxidized releasing CO2 , free H+,
& e- and forming ketoglutaric acid (5C)
Free e- reduce the energy carriers NAD+ to
NADH2 and FAD+ to FADH2
Ketoglutaric acid is also oxidized releasing
more CO2 , free H+, & eThe cycle continues oxidizing the carbon
compounds formed (succinic acid, fumaric
acid, malic acid, etc.) producing more CO2,
NADH2, FADH2, & ATP
H2O is added to supply more H+
CO2 is a waste product that diffuses out of
cells
Oxaloacetic acid is regenerated to start the
cycle again
NADH2 and FADH2 produced migrate to the
Electron Transport Chain (ETC)
Net Yield from Kreb's Cycle
(2 turns)
6
2
4
2
NADH2
FADH2
CO2
ATP
Electron Transport Chain:
• Found in the inner mitochondrial membrane or
cristae
• Contains 4 protein-based complexes that work
in sequence moving H+ from the matrix
across the inner membrane (proton pumps)
• A concentration gradient of H+ between the
inner & outer mitochondrial membrane occurs
• H+ concentration gradient causes the synthesis
of ATP by chemiosmosis
• Energized e- & H+ from the 10 NADH2 and 2
FADH2 (produced during glycolysis & Krebs
cycle) are transferred to O2 to produce H2O
(redox reaction)
O2 + 4e- + 4H+
2H2O
Energy Yield from Aerobic Respira
Glycolysis
Kreb's Cycle
Total
4 NADH2
0 FADH2
2 ATP
6 NADH2
2 FADH2
10 NA
2 FADH
2 ATP
38 ATP
• Most cells produce 36- 38 molecules of ATP
per glucose (66% efficient)
• Actual number of ATP's produced by aerobic
respiration varies among cells