AP Bio Exam Review:
Cell Energy
(Respiration & Photosynthesis)
• Catabolic pathways release energy by breaking
down complex molecules into simpler
compounds
• C6H12O6 +6O2
6H2O + 6CO2 +E
• Anabolic pathways consume energy to build
complex molecules from simpler ones
• 6H20+6CO2 + E
C6H12O6 +6O2
Concept 8.3 ATP powers cellular work by coupling exergonic
reactions to endergonic reactions
• A cell does three main kinds of work:
– Mechanical
– Transport
– Chemical
• To do work, cells manage energy resources by energy
coupling, the use of an
exergonic (energy releasing) process to drive an
endergonic (energy absorbing) one
Concept 8.4: Enzymes speed up metabolic
reactions by lowering energy barriers
A catalyst is a chemical agent that speeds up a reaction
without being consumed by the reaction
An enzyme is a catalytic protein
Hydrolysis of sucrose by the enzyme sucrase is an example
of an enzyme-catalyzed reaction
Substrate Specificity of Enzymes
• The reactant that an enzyme acts on is called the
enzyme’s substrate
• The enzyme binds to its substrate, forming an enzymesubstrate complex
• The active site is the region on the enzyme where the
substrate binds
Cofactors
Cofactors are nonprotein enzyme helpers such as
minerals
Coenzymes are organic cofactors such as vitamins
Enzyme Inhibitors
Allosteric Regulation
• a protein’s function at
one site is affected by
binding of a
regulatory molecule
at another site
• Allosteric regulation
may either inhibit or
stimulate an enzyme’s
activity
Feedback
Inhibition
• In feedback inhibition,
the end product of a
metabolic pathway
shuts down the
pathway
Energy Harvest
• Energy is released as electrons “fall” from
organic molecules to O2
• Broken down into steps:
Food  NADH  ETC  O2
– Coenzyme NAD+ = electron acceptor
– NAD+ picks up 2e- and 2H+  NADH (stores E)
– NADH carries electrons to the electron transport
chain (ETC)
– ETC: transfers e- to O2 to make H2O ; releases
energy
Cellular Respiration
Mitochondrion Structure
Citric Acid
Cycle
(matrix)
ETC
(inner membrane)
Glycolysis
Without O2
Fermentation
• Occurs in plants and
animals
• Occurs in cytosol
• Keep glycolysis going
• No oxygen needed
• Creates alcohol [+ CO2] or
lactic acid
O2 present
Respiration
• Release E from breakdown
of food with O2
• Occurs in mitochondria
• O2 required (final electron
acceptor)
• Produces CO2, H2O and up
to 38 ATP (NADH, FADH2)
Types of Fermentation
Alcohol fermentation
Lactic acid fermentation
• Pyruvate  Ethanol + CO2
• Ex. bacteria, yeast
• Used in brewing,
winemaking, baking
• Pyruvate  Lactate
• Ex. fungi, bacteria, human
muscle cells
• Used to make cheese,
yogurt, acetone, methanol
• Note: Lactate build-up does
NOT causes muscle fatigue
and pain (old idea)
PURPOSE = NAD+ recycled for glycolysis
Various sources of fuel
• Carbohydrates, fats and
proteins can ALL be
used as fuel for cellular
respiration
• Monomers enter
glycolysis or citric acid
cycle at different points
ENERGY
aerobic
(with O2)
glycolysis
anaerobic
(without O2)
(cytosol)
Respiration
(mitochondria)
Krebs cycle
(citric acid cycle)
electron
transport
chain
chemiosmosis
fermentation
Oxidative
Phosphorylation
ethanol + CO2
(yeast, some bacteria)
lactic acid
(animals)
Leaf cross section
Sites of Photosynthesis
Vein
Mesophyll
• mesophyll: chloroplasts
mainly found in these cells of
leaf
• stomata: pores in leaf (CO2
enter/O2 exits)
• chlorophyll: green pigment in
thylakoid membranes of
chloroplasts
Stomata
CO2 O2
Mesophyll cell
Chloroplast
5 µm
Outer
membrane
Thylakoid
Thylakoid
Stroma Granum
space
Intermembrane
space
Inner
membrane
1 µm
Photosynthesis = Light Reactions + Calvin Cycle
“photo”
“synthesis”
Light Reactions
Both respiration and photosynthesis use
chemiosmosis to generate ATP
Calvin Cycle = produce 3C sugar (G3P)
Photorespiration: low carbon-fixation when
stomata closed in hot, dry climate
C3
C4
CAM
C fixation & Calvin C fixation & Calvin in C fixation & Calvin at
together
different cells
different TIMES
Rubisco
PEP carboxylase
Organic acid
(normally fixes CO2)
fixes CO2
Mesophyll cells
Mesophyll: fix CO2
Bundle Sheath:
Calvin Cycle
Night: fix CO2 in 4C
acids
Day: Calvin Cycle
Ex. rice, wheat,
soybeans
Ex. sugarcane, grass
Ex. cacti, pineapple,
succulent
Comparison
RESPIRATION
PHOTOSYNTHESIS
• Plants + Animals
• Needs O2 and food
• Produces CO2, H2O and ATP,
NADH
• Occurs in mitochondria
membrane & matrix
• Oxidative phosphorylation
• Proton gradient across
membrane
• Plants
• Needs CO2, H2O, sunlight
• Produces glucose, O2 and ATP,
NADPH
• Occurs in chloroplast
thylakoid membrane &
stroma
• Photorespiration
• Proton gradient across
membrane