Ch. 8 Cellular Energy
I.
How Organisms Obtain Energy
Main Idea: All living organisms use energy to carry out all biological
processes.
A. Transformation of Energy
1. energy: the ability to do work
2. thermodynamics: study of the flow and transformation
of energy in the universe
a. law of conservation of energy (1st law): energy
can be converted from one form to another, but not
created or destroyed
b. Entropy (2nd law): energy can’t be converted
without the loss of usable energy; entropy is the
measure of disorder, or unusable energy, in a
system.
3. autotrophs: organisms that make their own food
usually from the sun
a. chemoautotrophs: use inorganic substances like
hydrogen sulfide as a source of energy
b. photoautotrophs: convert light energy into
chemical energy (ex. Plants)
4. heterotrophs: organisms that need to ingest food to
obtain energy
B. Metabolism: all the chemical reactions in a cell
1. metabolic pathway: a series of chemical reactions in
which the product of one reaction is the substrate for
the next reaction.
a. catabolic pathway: release energy by breaking
down larger molecules into smaller molecules (ex:
cellular respiration)
b. anabolic pathway: use energy released by
catabolic pathway to build larger molecules from
smaller molecules (ex: photosynthesis)
2. photosynthesis: anabolic pathway in which light energy
is converted to chemical energy for use by the cell
3. cellular respiration: catabolic pathway in which
organic molecules are broken down to release energy
for use by the cell.
C. ATP: the unit of cellular energy
1. ATP (adenosine triphosphate): the most important
biological molecule that provides chemical energy for
the cell.
a. Most abundant energy-carrier molecule in cells
and is found in all types of organisms.
b. releases energy when the bond b/w the second and
third phosphate is broken and ADP (adenosine
diphosphate) is formed with a free phosphate
group.
II.
Photosynthesis
Main Idea: Light energy is trapped and converted into chemical energy
during photosynthesis.
A. Overview
6CO2 + 6H2O ------C6H12O6 + 6O2
1. photosynthesis occurs in 2 phases:
a. phase 1: light-dependent reactions where light is
absorbed then converted to chemical energy
molecules ATP and NADPH
b. phase 2: light-independent reactions where energy
molecules are used to make glucose.
Phase One: Light Reactions
2. chloroplasts: organelles that capture light energy, found
mostly in the cells of leaves
a. thylakoids: flattened saclike membranes arranged
in stacks called grana
b. stroma: fluid-filled space outside the grana where
phase 2 occurs.
3. pigments: light-absorbing colored molecules found in
thylakoid membrane of chloroplasts
a. chlorophyll a and b: absorb light strongly in the
violet-blue region of visible light spectrum and
reflect light in the green region
b. carotenoids: accessory pigments (ex: betacarotene); Absorb mainly blue-green light, reflect
yellow-orange.
o Some pass energy to chlorophyll a
o Some absorb and dissipate excessive light
energy that would otherwise damage
chlorophyll.
4. Electron Transport: occurs in thylakoid membrane
a. Photosystem 1 and 2: protein complexes that
contain light-absorbing pigments and proteins
important for the light reaction located in thylakoid
membrane.
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1) Photosystem II absorbs energy from a photonexcited
electron.
2) The excited electron is passed between pigment molecules
until it reaches the reaction center.
3) The electron is passed to the primary electron acceptor.
4) The electron is replaced in Photosystem II by an electron from
a water molecule.
5) The first electron is passed down the ETC to Photosystem
Ian H+ gradient is created, providing energy for ATP
production via chemiosmosis.
6) Photosystem I absorbs energy from light and passes a new
excited electron to the reaction center.
7) This second excited electron is passed to a 2nd ETC.
8) The first electron (from photosystem II) replaces the lost
electron from Photosystem I.
9) This process repeats.
10) The 2 electrons that have now left Photosystem I are used to
make a molecule of NADPH from NADP+.
11) The water molecule has been broken apart into one oxygen
atom and two H+ ions.
12) This entire process repeats.
13) Final products are: ATP, 2 NADPH, and O2.
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Light + 2 H2O + 2 NADP+  O2 + 2 H+ + 2 NADPH + ATP
4. chemiosmosis: the production of ATP during electron transport.
a. H+ (protons) build up on the thylakoid interior creating a
concentration gradient
b. H+ follow the concentration gradient and exit the
thylakoid membrane into the stroma through ion
channels called ATP synthases that produce ATP
in the process.
[DRAW LIGHT REACTION ELECTRON TRANSPORT CHAIN
DIAGRAM]
Phase Two: the Calvin Cycle
 Inputs:
o CO2 (From the air)
o ATP (From the light reactions)
o NADPH (From the light reactions)
 Products:
o G3PGlucose
o ADP
o NADP+
 To synthesize one glucose molecule, the Calvin cycle must
complete 6 cycles.
o Uses 6 CO2 molecules
o Uses 18 molecules of ATP
o Uses 12 molecules of NADPH
 The sugars produced can be used in cellular respiration,
stored as cellulose or starch, or converted to other organic
compounds.
1. The Calvin Cycle converts the energy molecules ATP and NADPH
made in phase I into organic molecules like glucose.
2. rubisco: converts inorganic carbon dioxide molecules into organic
molecules that can be used by the cell.
3. plants use the sugars made in the Calvin Cycle as a source of
energy and building blocks for complex carbohydrates (ex: cellulose).
III. Cellular Respiration
Main Idea: Living organisms obtain energy by breaking down organic
molecules during cellular respiration.
A. Overview
1. the purpose of cellular respiration is to harvest electrons from
carbon compounds and use that energy to make
ATP.
o The aerobic harvesting of energy from food molecules by cells.
1) Aerobic: Oxygen-containing
2) Anaerobic: Oxygen-lacking
Generally: Sugar + O2  Energy + CO2
C6H12O6
Glucose
+
6 O2
Oxygen

6 CO2
Carbon
Dioxide
+
6 H2O
+
ATPs
Energy
 Each ATP molecule contains 1% of the energy in a glucose molecule.
 Cells store 40% of glucose’s energy in ATP molecules. The rest is
converted (lost) to heat.
 Our bodies use up to 75% of the energy we take in each day just to
maintain our body.
22.. M
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& SSTTOORRAAGGEE
 Respiration works by shuttling electrons through a series of energyreleasing reactions.
 We can “see” the movement of electrons by watching the movement
of hydrogen atoms (which each contain 1 electron and 1 proton).
R
REEDDOOXX R
REEAACCTTIIOONNSS
Oxidation: The loss of
electrons from one
substance (oxidized).
Reduction: The
addition of electrons to
another substance
(reduced).
3.Cellular respiration occurs in 2 stages:
a. glycolysis: anaerobic process (no oxygen)
b. aerobic respiration: includes the Krebs
cycle (citric acid cycle) and electron
transport (uses oxygen)
 occurs in cytoplasm of prokaryotes
 occurs in mitochondria in
eukaryotes
B.Glycolysis n {white board]
1. glucose is broken down in the cytoplasm
2. 2 molecules of pyruvate (3-carbon molecule)
and 4 molecules of ATP are produced.
[DRAW GLYCOLYSIS DIAGRAM ON WHITEBOARD]
C.Krebs Cycle (citric acid cycle):
1.glycolysis produces 2 pyruvate molecules that form 2
acetyl CoA molecules so 1 glucose molecule allows 2
turns of the Krebs Cycle
5. 2 turns produces:
8 NADH
2 FADH2
2 ATP
6 CO2 (waste)
[DRAW KREBS CYCLE DIAGRAM ON WHITEBOARD]
B. Electron Transport [copy picture on whiteboard]
1. final step in breakdown of glucose in aerobic
respiration
2. occurs in inner mitochondrial membrane
3. high-energy electrons and hydrogen ions from NADH
and FADH2 produced in the Krebs cycle are used to
convert ADP to ATP
4. in eukaryotes, 1 molecule of glucose yields 36 ATP
5. in prokaryotes, 1 molecule of glucose yields 38 ATP.
Steps:
a. electrons in H atoms of NADH and FADH2 are at
high energy levels
b. high energy electrons passed down chain protein to
protein, losing some of their energy
c. energy is used to pump H+ atoms from
mitochondrial matrix to other side of inner
mitochondrial membrane
d. buildup of H+s in space between outer and inner
mitochondrial membrane
e. ATP synthase makes ATP from ADP as protons
move down their concentration gradient into
mitochondrial matrix.
O2 – final electron acceptor
O2 + 4e- + 4H+ = 2H2O
PPOOIISSOONNSS
 Electron Transport Chain Blockers
o Rotenone: Blocks one of the 1st electron carriersNo H+
gradientNo ATP
o Cyanide & Carbon Monoxide: Block the passage of electrons
to oxygen.No H+ gradientNo ATP
 ATP Synthase Inhibitors
o Oligomycin: Blocks H+ ions from moving through the channel
in ATP synthaseNo ATP is made.
 Uncouplers
o Dinitrophenol (DNP): Makes the mitochondrial membrane
leaky to H+ ETC continues, but no ATP is made.
C. Anaerobic Respiration
1. fermentation: in the absence of oxygen, some cells
convert glucose into lactic acid or ethyl alcohol
a. occurs in cytoplasm
b. regenerates cell’s supply of NAD+ while producing
a small amount of ATP.
c. 2 types of fermentation:
i. lactic acid fermentation: enzymes that convert
the pyruvate made in glycolysis to lactic acid
by transferring high-energy electrons and
protons from NADH
 produced in skeletal muscles under hard
exercise causing fatigue
 milk ferments naturally by “spoiling”
 certain types of bacteria that produce
lactic acid are used to make cheese,
yogurt, buttermilk and sour cream
[DRAW LACTIC ACID FERMENTATION DIAGRAM]
ii. alcohol fermentation: occurs in yeast and
some bacteria where pyruvate is converted
to ethyl alcohol and CO2
[DRAW ALCOHOL FERMENTATION DIAGRAM]