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Cellular Respiration
C6H12O6 + 6O2 -----> 6CO2 + 6H20 + energy (heat and
ATP)
Energy
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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
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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.
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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)
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Energy carrying molecule used by cells to fuel their cellular
processes
ATP is composed of an adenine base, ribose sugar, & 3 phosphate
(PO4) groups
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The PO4 bonds are high-energy bonds that require energy to be
made & release energy when broken
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ATP is made & used continuously by cells
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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
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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:
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Biological catalysts
Speeds up chemical reactions
Lowers the amount of activation energy needed by weakening
existing bonds in substrates
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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:
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Has outer smooth, outer membrane & folded 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
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Electron Transport Chain takes place in cristae
Cellular Respiration Overview:
C6H12O6 + 6O2 -----> 6CO2 + 6H20 + energy (heat and
ATP)
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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:
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Occurs in the cytoplasm; ALL ORGANISMS!
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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.
Net Yield from Glycolysis
and Pyruvate Oxidation (preKrebs)
4 NADH
2 CO2
2 ATP (Substrate level phosphor.)
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+ (oxidation)
so it is available for step c above. This keeps glycolysis going!
Alcoholic Fermentation
Lactic Acid Fermentation
Aerobic Respiration:
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Occurs in the mitochondria
Includes the Krebs Cycle & the Electron Transport Chain
Before Krebs, PYRUVATE OXIDATION (Pre-Krebs) occurs:
1-Pyruvic acid (pyruvate) from glycolysis diffuses into matrix of
mitochondria & reacts with coenzyme A to for acetyl-CoA (2-carbon
compound)
2- CO2 and NADH are also produced
Kreb's Cycle:
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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/Oxaloacetate (4C) to make 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 NADH and FADH+ 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,
NADH, 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
NADH and FADH2 produced migrate to the Electron Transport
Chain (ETC)
Net Yield from Kreb's Cycle
(2 turns)
6 NADH
2 FADH2
4 CO2
2 ATP
Electron Transport Chain:
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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 (through ATP synthase)
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Energized e- & H+ from the 10 NADH 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 Respiration
Glycolysis&PreKreb Kreb's Cycle
Total
4 NADH
0 FADH2
2 ATP
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6 NADH
2 FADH2
2 ATP
10 NADH x 3 = 30 ATP
2 FADH2 x 2 = 4 ATP
4 ATP
38 ATP
Most cells produce 36- 38 molecules of ATP per glucose (66%
efficient)
Each NADH makes 3 ATP; FADH2 makes 2 ATP. Why??
Actual number of ATP's produced by aerobic respiration varies
among cells