Chapter 5
Section 5-1
*Directly or indirectly, all energy needed for
metabolism comes from the SUN
*Energy enters living systems when plants, algae
and bacteria absorb sunlight
*Some energy from the sun is captured to make
organic compounds which are then stored
*Metabolism either uses energy to
build molecules or break down
molecules that store energy
*Photosynthesis is the process by which light energy
is converted to chemical energy
*Autotrophs are organisms that use energy from
sunlight or inorganic substances to make organic
compounds
*Most autotrophs like plants are photosynthetic
*Chemical energy in organic compounds can
transfer to organisms that consume those
compounds
*Heterotrophs are organisms that must get
energy from food instead of directly from
sunlight or inorganic substances
*Cellular respiration is a metabolic process
where organisms harvest energy from food
*Cells burn energy differently than wood
burns
*In cells, stored energy is released in a series
of enzyme assisted reactions
*When cells break down food molecules,
some energy is released as heat, most is
released as ATP
*ATP (adenosine triphosphate) is a nucleotide
with 2 energy storing phosphate groups
*Phosphate groups store energy like a spring
and releases it when the bonds holding the
groups together break
*ATP
ADP + P + Energy
Section 5-2
*Plants, algae and some bacteria
capture 1% of the energy in the
sunlight that reaches Earth
*Stage 1: Energy is captured from sunlight
*Stage 2: Light energy is converted to chemical
energy; stored as ATP and the energy carrier
molecule NADPH
*Stage 3: Energy from ATP and NADPH powers the
formation of organic compounds using carbon dioxide
(CO2)
*6CO2 +6H2O
Light
C6H12O6+ 6O2
*First and second stage of
photosynthesis are light stages
*Without light, these reactions would
not occur
*Light energy is used to make energy
storing compounds
*Pigments are molecules that absorb certain
wavelengths of light and reflect others
*Chlorophyll is the primary pigment involved in
photosynthesis and it absorbs red and blue and
reflects green and yellow
*Carotenoids are pigments that produce yellow and
orange fall leaf colors
*Using both carotenoids and chlorophyll absorbs more
light energy, so plants use both
*Pigments used in photosynthesis are found in
the chloroplast
*Clusters of pigments are embedded in diskshaped structures called thylakoids
*When light strikes a thylakoid, energy is
transferred to electrons in pigments and the
electrons are excited
*Excited electrons jump from pigment
molecules to others and power second stage
of photosynthesis
*The electrons must be replaced so water
molecules split, taking electrons from
hydrogen, leaving H+ and oxygen O which
forms oxygen gas
Section 5-3
*Cellular respiration harnesses the energy in
organic compounds
*C6H12O6 +602  6CO2 + 6H2O + energy
*Primary fuel for cellular respiration is glucose
*Glucose is formed when starch or sucrose are
broken down
*Glucose (sugar) is broken down in the
cytoplasm by the process glycolysis
*Glycolysis is an enzyme assisted anaerobic
process that breaks down one 6-carbon
molecule of glucose to two 3-carbon
pyruvates
*Glycolysis uses 2 ATP molecules but produces
4 ATP molecules
*Step 1: Phosphate groups from 2 ATP
molecules are transferred to glucose
*Step 2: The 6-carbon compound is broken
down into two 3-carbon compounds + 1
Phosphate
*Step 3: Two NADH molecules are made 1
more phosphate group is added
*Step 4: Each 3 carbon compound is
converted to 3-carbon pyruvates, which
produces 4 ATP
*When oxygen is present, pyruvate from glycolysis
enters a mitochondria and is converted to a 2
carbon compound
*This produces CO2, one NADH and a 2-carbon
acetyl group
*This attaches to an enzyme A (CoA) making
acetyl-CoA
*Acetyl-CoA enters a series of enzyme-assisted
reactions called Krebs Cycle
*Step 1: Acetyl-CoA combines with a 4-C comp,
making a 6-C comp and releasing CoA
*Step 2: CO2 is released from the 6-C comp
forming a 5-C comp. e- transfer making NADH
*Step 3: CO2
is released from 5-C comp, making a
4-C, ATP and NADH
*Step 4: 4-C comp is converted to another, and etransfer to make electron carrier, FADH2
*Step 5: 4-C comp is converted to original 4-C
comp, NADH is produced and cycle can start over
*In aerobic respiration, electrons donated by
NADH and FADH2 pass through electron
transport chains
*The chain pumps H+ out of the
mitochondria which combines with O2 to
make H2O
*ATP is produced as H+ diffuses back into
the mitochondria
*Without enough oxygen, Electron Transport
Chain does not function the same
*O2 receives electrons and when not present,
NADH and NAD+ cannot be recycled
*So NAD+ undergoes fermentation to recycle it
*Lactate is the ion of an organic acid
called lactic acid
*A 3-C pyruvate converts to a 3-C lactate
in order to continue glycolysis to produce
ATP
*3-C pyruvate is broken down to ethanol, a 2-C
compound during alcoholic fermentation
*CO2 is released
*Electrons transfer from NADH to the 2-C
compound producing ethanol
*NAD+ is recycled to continue glycolysis
*The total amount of ATP harvested from each glucose
molecule depends on oxygen
*Cells use energy more efficiently when oxygen is present
*In stage 1: glucose is broken down by glycolysis (anaerobic)
and gains 2 ATP
*In Stage 2: pyruvate passes thru aerobic respiration or
(anaerobic) fermentation
*In fermentation, small amounts of ATP is produced
*In respiration, up to 2 ATP are produced by Krebs cycle
and 34 through electron transport chains