Transcript Energy in a Cell

Energy in a Cell
Chapter 9
Why do our cells need
energy?
Active transport
Cell division
Movement of cilia and
flagella
The production and
storage of proteins
Contracting skeletal,
cardiac and smooth
muscles
Messages sent from the
brain
Adenosine Triphosphate
(ATP)
Structure: adenosine molecule with 3
phosphates attached
The energy is stored in the bonds
between each phosphate;
– Each phosphate has the same charge
– When the phosphates bond, a HUGE
amount of energy is required to hold them
together since they do not attract.
How do cells tap into the energy stored in the
bonds between the phosphates of the ATP
molecule?
When ATP loses its last phosphate, the energy stored between
the 2nd and 3rd phosphate is released. This is the source of
energy for the cell.
Adenosine Diphosphate (ADP) is then formed.
Eventually, another phosphate will bond to ADP forming ATP
which can be used for energy again.
Sometimes cells will use ADP for energy by breaking the second
phosphate off of the molecule. The energy stored between the
1st and 2nd phosphate is release. This, however, is not efficient
since there is not as much energy stored between these
phosphates.
Refer to Figure 9.2 (page 229)
Where does this ATP come
from?
The sun is the source of all
energy!
Chlorophyll, a pigment found in the chloroplasts
of plant cells, captures sunlight energy which
drives photosynthesis.
Heterotrophs do not contain chlorophyll,
therefore, these organisms must rely on green
plants to transform sunlight energy into chemical
energy (ATP).
Photosynthesis
Light-Dependent
Reactions:
– After capturing sunlight
energy, chlorophyll
passes energy down an
electron transport chain.
– Half of the energy is used
to split water releasing
oxygen and forming
NADPH
– Half of the energy is used
to form ATP
– NADPH and ATP are
needed for lightindependent reactions.
Light-Independent
Reactions:
– During the Calvin cycle,
which takes place in the
stroma of chloroplasts,
the carbon in CO2 is
used as well as the ATP
and NADPH from the
light-dependent reactions
to form carbohydrates
through a series of
reactions (page 235).
– It takes a total of 6
rounds to form 1 sugar
molecule.
Photosynthesis
6CO2 + 6H2O
C6H12O6 + 6O2
The sunlight energy is now
chemical energy trapped in
the carbohydrate, glucose!
So, how do cells release the
energy in glucose?
Cellular Respiration
Glycolysis
– A series of chemical reactions in the cytoplasm of the cell that breaks
down glucose into 2 molecules of pyruvic acid.
– 4 molecules of ATP are produced but 2 are used from earlier reactions for
glycolysis to occur; therefore, the net gain of ATP is only 2 ATP
molecules.
– NADH and H+ are also formed which will be used in the citric acid cycle.
Following glycolysis, the pyruvic acid molecules move
to the mitochondria of the cell.
Within the mitochondria of the cell, the pyruvic acid
formed during glycolysis is converted into acetyl-CoA
– During this process, a molecule of CO2 is released.
– NADH + H+ are formed for use in the citric acid cycle.
Cellular Respiration
The Citric Acid Cycle
– A molecule of acetyl-CoA is broken down, forming ATP and
CO2 through a series of reactions.
– NADH + H+ and FADH are also formed for use in the final
step, the electron transport chain.
The Electron Transport Chain
– NADH and FADH2 pass energized electrons from protein to
protein within the inner membrane of the mitochondria.
– Oxygen in the chain combines with H+ to form water.
– 32 molecules of ATP are produced making this process very
efficient.
Cellular Respiration
C6H12O6 + 6O2
6H2O + 6CO2 +36ATP
What if oxygen is not present?
Lactic Acid
Fermentation
– Glycolysis occurs
– Instead of water and
carbon dioxide, lactic
acid is produced.
– Only 2 molecules of
ATP are produced
Alcoholic Fermentation
– Glycolysis occurs
– Instead of water, alcohol
is produced.
– Only 2 molecules of ATP
are produced
– This process is done by
yeast cells. Since CO2 is
produced, yeast is used
to make dough rise.
Compare Photosynthesis and
Respiration