Chapter 9
Energy in a Cell
• Cells need energy, its essential to life
• Our body has a source of energy
available to us
• The energy is stored in the chemical
bonds of ATP
9.1 ATP in a molecule
• ATP = adenosine triphosphate
– Adenosine molecule
– Three phosphates
• ATP is a small compound that is a
quick source of energy
• Binds to specific sites on a cell
• When phosphate bond broken,
energy is released – cell uses this
energy
ADP
Adenosine Diphosphate
• Formed when a phosphate is cleaved
from ATP
– Releases energy
• ADP can reform ATP which creates
a renewable cycle of ATP formation
and breakdown
• This cycle continues as long as there
are phosphate molecules available
What do you think would happen if
there were no more phosphate
molecules available?
• ATP binds to a molecule
• Phosphate group is cleaved off and
ADP leaves
– Phosphate group gives the cell its
energy
• Another ADP molecule binds to the
phosphate molecule and the process
starts over
• Cells use the energy for many
purposes
– Physical activity
– Making new enzymes to carry out
chemical reactions
– Build membranes and cell organelles
– Maintain homeostasis
– Dispose of waste substances
9.2 Photosynthesis:
Trapping the Sun’s Energy
• Photosynthesis
• 6CO2 + 6H2O  C6H12O6 + 6O2
– Converts light energy into chemical
energy
– two phases
• Light-dependent + light-independent
– Builds carbohydrates that store energy
– Produces ATP
– Occurs in membranes of thylakoid discs
• Thylakoid discs
– Located in chloroplasts
– contain pigments that absorb light =
chlorophyll
Light-dependent Reactions
• First phase of photosynthesis
• Sunlight hits plants and they absorb
energy
• Transfer energy to electrons on the
Electron Transport Chain
• Electron Transport Chain is a series
of proteins embedded in thylakoid
membrane
• In the ETC, Energy is passed from
protein to protein
• Each transfer a little bit of energy is
released
• This energy is used to form ATP
from ADP
• The ETC also splits a water molecule
and hydrogen ions, H+, bind with an
NADP+ molecule forming NADPH
• NADPH is used to form
carbohydrates in light-independent
reactions
Light-independent Reactions
• Calvin Cycle
– Takes place in the stroma of the
chloroplast
– 5 steps – page 235
– Each step adds a CO2 molecule
– Takes 6 cycles to form a sugar
9.3 Getting energy to make
ATP
Cellular Respiration
• 3 stages
– Glycolysis
– Citric acid cycle
– Electron transport chain
Glycolysis
• Anaerobic – no oxygen
• Occurs in the cytoplasm
• Break down glucose into pyruvic
acid
• ATP – 2 used, 4 produced; net gain
of 2 molecules
• Pyruvic acid molecules move to
mitochondria, loses a molecule of
CO2 and combines with
coenzyme A to form acetyl-CoA
The Citric Acid Cycle
• Glucose is broken down
• One ATP molecule formed
• Charged electrons are carried via
NADH & FADH2 to the electron
transport chain in the mitochondria
The Electron Transport Chain
• Energized electrons passed from
protein to protein
• Mitochondria inner membrane
becomes positive charged, due to
high concentration of H+ ions
• Mitochondria outside membrane
becomes negatively charged due to
electrons on the outside
• A concentration gradient occurs:
electrical & chemical
• Electrical = charge difference
• Chemical = concentration difference
• Inner membrane of mitochondria
forms ATP
• Final electron acceptor is Oxygen
• 32 ATP molecules formed
• 35 ATP produced overall
• Glycolysis
– 2 ATP
• Citric Acid Cycle
– 1 ATP
• Electron Transport Chain
– 32 ATP
Fermentation
Lactic Acid Fermentation
• 2 molecules of pyruvic acid use
NADH to form 2 molecules of lactic
acid
• 2 molecules ATP produced
• Muscle fatigue = lactic acid build-up
Alcoholic Fermentation
• Yeast cells produce CO2 and ethyl
alcohol
• Bread – yeast cells produce carbon
dioxide that forms bubbles in dough,
heat kills CO2 & bubbles in dough
lighten bread
Photosynthesis vs. Cellular Respiration
• Food
accumulated
• CO2 taken in
• Energy stored in
glucose
• Occurs only in
light
• Occurs only in
presence of
chlorophyll
• Food broken
down
• CO2 given off
• Energy released
from glucose
• Occurs day &
night
• Occurs in all
living cells
The End