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Energy in the Cell
Ch. #9 Sect. 1
-To maintain homeostasis
-To transmit nerve impulses
-To build and repair
-To power cell movement
A. Cell Energy
--All biological work demands energy
--Energy is the ability to do work
--Our cells get energy from foods
--Food is broken down into energy
and used to make ATP
B. Exergonic Reactions
--Chemical reactions that release free energy
--In biological systems, the breakdown of
food provides free energy
--Biological systems store the free energy
in the form of ---ATP
C. Endergonic reactions
-Biological activity or work requires
Free Energy
-Uses Free Energy stored in ATP to do the
activity
-Examples:
-build structures or compounds
-transport materials across the cell membrane
-cell or body movement
-transmit nerve signals
1. ATP

ATP = Adenosine Triphosphate
– Composed of
1. a nitrogen base called Adenine
2. the sugar Ribose
3. three phosphate groups attached to the Ribose
– Potential Energy is stored in the phosphate bonds
When free energy is needed to do work, ATP
is broken down to release it’s stored energy
ATP + H20  ADP + Pi + Free energy (hydrolysis)
Free energy is used for
endergonic reactions.
1. Maintain body temperature
2. Active transport
3. All enzyme activity
4. other processes that build
biological structure
2. ADP
ADP= Adenosine Diphosphate
--Contains adenine, ribose and two
phosphate groups
--Has less potential energy than ATP
because it has one less phosphate bond
ADP + Pi + energy  ATP + H2O (condensation)
From food
Energy from exergonic reactions are stored as
potential energy in the phosphate bonds of ATP
3. Exergonic/Endergonic Coupled Reactions
Exergonic breakdown of ATP provides free energy to
drive endergonic reactions that require energy
ATP + H2O
ADP + Pi (exergonic)
Free Energy
Glucose + Fructose
Sucrose (endergonic)
In living systems, most processes use this coupling
of reactions to function
Sect. 3
D. Cell Respiration Replenishes ATP
During cell respiration:
1. energy is released by breaking the bonds
of food molecules (glucose)
2. the released energy (free energy) is used
to make ATP.
Two parts of Cell Respiration
I. Anaerobic:
--respiration not requiring oxygen
--occurs in the cytoplasm
--produces 2 net ATP (from one glucose)
II. Aerobic:
--respiration requiring oxygen
--occurs in the mitochondria
--produces 34 net ATP (from one glucose)
E. Cellular Respiration
I. Anaerobic (no oxygen)
1. First step : Glycolysis
--Occurs in cytoplasm
--Glucose is split into two 3-carbon molecules
(PGAL)
--2 ATP and enzymes are used to split the
glucose
--the two PGAL molecules are converted
into two Pyruvic Acids producing 4 ATP
+4 ATPs are produced from glycolysis
-2 ATPs used to start glycolysis
2 net ATPs are produced by glycolysis
II. Aerobic (with oxygen)
--The two Pyruvic Acids are then transported
into a near by mitochondria
2. Pyruvic Acid Conversion:
--Two Pyruvic Acids are converted into
two Acetyl CoA molecules
II. Aerobic (with oxygen)
3. Citric Acid Cycle
--Occurs in the Mitochondria
--Each acetyl CoA combines with a 4-carbon Oxaloacetic acid
molecule to make a 6-carbon molecule (Citric Acid)
--The 6-carbon molecule is broken down to
produce a 4-carbon molecule and releases CO2
--The electron carriers NADH and FADH2 are made
--only 2 ATP are made in Citric Acid Cycle
(from one Glucose!!!)
one 2-carbon
Acetyl CoA
--Only one Acetyl CoA can enter
the Citric Acid Cycle at a time
6-carbon
Citric Acid
4-carbon
Oxaloacetic
acid
Citric Acid Cycle
-CO2
-NADH
-NADH
-FADH2
-ATP
-NADH
-CO2
4. Electron Transport Chain (ETC):
--FADH2 and NADH are energy carriers
--They deliver electrons to the top of the ETC staircase.
--As electrons move down the staircase, they release energy.
--The released energy is used to make ATP
--Hydrogen combines with oxygen to
make water at the bottom of the staircase
to complete the process
--32 ATP are made in ETC
1. in cytoplasm (anaerobic) Glycolysis
net gain of 2 ATPs
2. in mitochondria (aerobic) Citric Acid Cycle
gain of 2 ATPs
3. Final step in mitochondria (aerobic) ETC
net gain of 32 ATPs
TOTAL : 36 net ATPs from one Glucose
Cellular Respiration produces
36 net ATPs
1. H+ ions combine with O2 to form waste H2O in ETC.
Without the oxygen to accept the H+ ions, the ETC will
shut down and we will die!! Quickly!!!
2. Waste CO2 is formed during the Citric Acid Cycle
3. Electron carriers for the ETC are produced in
the Citric Acid Cycle
Special types of Anaerobic Respiration
1. Lactic acid Fermentation (muscle cells and bacteria)
--Converts glucose into lactic acid
--Other products are CO2 and 2 ATP’s
-- Too much Lactic Acid causes muscle fatigue
during physical activity
--Occurs in production of sour cream,
sauerkraut and cheese
Oxygen Debt
--The oxygen that is owed to the body, after
exercise produces excess lactic acid, so it can be
converted back to pyruvic acid.
--This is why you keep breathing very deep even
after you have stopped running or exercising.
The extra oxygen that you are breathing is used
to convert the stored lactic acid in muscles
back into pyruvic acid which can then be
converted to acetyl CoA and then sent
to the mitochondria for Aerobic breakdown.
2. Alcohol Fermentation (in bacteria and yeast)
--Converts glucose to Ethyl Alcohol
--other products include CO2 and 2 ATPs
--Occurs in the production of wine, beer and breads
In the production of breads, yeast,
sugar and water are added to the
dough mix. The mixture is allowed to
rise for a period of time. The yeast
breaks down the sugar producing CO2
which causes the dough to “rise”.
The dough is then cooked in this
inflated form. This is how you get
‘holes’ in your bread.
Comparision of Photosynthesis
and Cell Respiration
Photosynthesis
 Endergonic reactions
 Occurs in plants
(chloroplast)
 Uses CO2 and H2O
 Produces Glucose
and Oxygen
Cell Respiration
 Exergonic reactions
 eukaryote cytoplasm and
mitochondria
 Uses glucose and O2
 Produces CO2 and H2O