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Cellular Energy
The First Law of Thermodynamics
• first law of thermodynamics
– Energy can be transferred and transformed, but it
cannot be created or destroyed
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin
Cummings
The Second Law of Thermodynamics
• second law of thermodynamics:
– Every energy transfer or transformation increases
the entropy (disorder) of the universe
During every energy transfer or transformation,
some energy is unusable, and is often lost as
heat
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin
Cummings
Fig. 8-3
Heat
Chemical
energy
(a) First law of thermodynamics
CO2
+
H2O
(b) Second law of thermodynamics
Cell Energy
• Energy is essential to life
• All living organisms must be able to
produce energy, store energy and use
energy
• Cells need a a quick source of energy
• Cellular energy is stored in chemical
bonds of the ATP molecule
ATP
• ATP = Adenosine triphosphate
• Adenosine molecule with 3 phosphate
groups attached
Adenosine
P
P
P
Fig. 8-8
Adenine
Phosphate groups
Ribose
ATP
• The charged phosphate groups act like the
positive poles of two magnets, they repel
each other
• Energy is contained in the bond that holds
the phosphate molecules to the adenosine
• When a bond breaks, energy is released
resulting in ADP (adenosine diphosphate)
• Refer to pg 229 fig 9.2
An organism’s metabolism transforms matter
and energy, subject to the laws of
thermodynamics
• Metabolism is the totality of an organism’s
chemical reactions
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin
Cummings
Organization of the Chemistry of Life into
Metabolic Pathways
Enzyme 1
Enzyme 2
B
A
Reaction 1
Starting
molecule
Enzyme 3
C
Reaction 2
D
Reaction 3
Product
A metabolic pathway begins with a specific molecule and
ends with a product. Each step is catalyzed by a specific
enzyme
• Catabolic pathways release energy by
breaking down complex molecules into
simpler compounds
– Cellular respiration, the breakdown of glucose
in the presence of oxygen, is an example of a
pathway of catabolism
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin
Cummings
• Anabolic pathways consume energy to
build complex molecules from simpler ones
– The synthesis of protein from amino acids is an
example of anabolism
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin
Cummings
Photosynthesis
• Absorbing light energy and converting it
into stored chemical energy (plants &
algae)
• Principal product = glucose (O2 – major
by-product)
• Takes place in chloroplast
Photosynthesis cont.
• Sun – ultimate source of
energy
• Because photosynthesis is
the essential step between
solar energy and life – it
is one of the most
important biological
processes.
Photosynthesis
• To use the energy solar energy, plant cells
must trap light energy and store it in a
form that is readily usable by the cell
(ATP)
• Because light is not available 24 hours a
day, the plant must have some way to
store energy for later use 
photosynthesis
Photosynthesis
• Photosynthesis happens in two phases
– Light dependent reaction
• Conversion of light energy into chemical energy
• Produces ATP
– ATP immediate use by the plant
– Light independent reaction
• Uses ATP to produce glucose
– Glucose - stored energy for later use
Chemical equation for
photosynthesis
chlorophyll
CO2 + H2O + light energy  glucose + H2O + O2
Chlorophyll a
6CO2 + 12H2O + light energy  C6H12O6 + 6O2 + 6H2O
Most of us don't speak chemicalese, so the above chemical equation translates as:
six molecules of water plus six molecules of carbon dioxide produce one molecule of
sugar plus six molecules of oxygen
Chloroplast
• Chloroplast – cell organelle where
photosynthesis occurs
• Composed of Thylakoids in stacks (Grana), with
space around (Stroma)
• Chlorophyll is found in the membranes of the
thylakoids
Chlorophyll
• A green-colored pigment
• Primary catalyst of photosynthesis
• There are at least 4 different types of
chlorophyll (a, b, c, d)
• Found in Chloroplasts
Structure of Chloroplast
• Thylakoid is the
structural unit of
photosynthesis.
Thylakoids are
stacked like pancakes
in stacks known
collectively as grana.
The areas between
grana are referred to
as stroma.
• Chlorophyll is found
in the grana
Light Dependent Reaction
AKA:Photo Phase
• Step 1: Light energy is absorbed and energizes a
chlorophyll molecule
• Step 2: Water molecules are split
– Photolysis: breaking apart of a water molecule by
energized chlorophyll
• Step 3: Oxygen is released
• Step 4: Hydrogen is bonded to hydrogen
acceptor (NADP)
• Step 5: ATP molecule is made (energy is stored
in ATP)
The Electron Transport Chain and Chemiosmosis
Biology, Sixth Edition
Chapter 8,
Light Independent Reaction
AKA: Dark Phase
• Step 1: CO2 is bonded to RuBP
– RuBP (ribulose biphosphate) – 5 carbon sugar with 2 phosphates
– Resulting 6-carbon sugar is unstable and breaks to form 2 molecules
of PGA (phosphoglyceric acid)
– PGA is a 3-carbon sugar with a phosphate attached to it
• Step 2: PGA is converted to PGAL
– PGA receives hydrogen and is energized by energy and phosphate
from and ATP molecule
• Step 3: Water is given off
• Step 4: PGAL is converted to glucose
The Calvin Cycle:
Phases 1 & 2
1. Carbon uptake
– Adds carbon dioxide to 5C
ribulose bisphosphate (RuBP)
– Catalyzed by RUBISCO;
ribulose bisphosphate
carboxylase
2. Carbon reduction phase
– Citrate is made and broken to
form phosphoglycerate (PGA)
– PGA is rearranged and
phosphorylated by ATP
– NADPH reduces the
backbone further to form
glyceraldehyde-3-phosphate
(G3P)
Biology, Sixth Edition
Chapter 8,
The Calvin
Cycle:
Phase
3
3. Reformation of RuBP:
•
– G3P is rearranged,
– & phosphorylated
– With further investment
of ATP…
– To make RuBP, a
bisphosphorylated
compound
Alternatively,
– G3P is shuttled out of the
cycle to produce glucose
and other carbohydrates
elsewhere
Biology, Sixth Edition
Chapter 8,
Partition of Function in the Chloroplast
• The light-dependent reactions (the harvesting of
light) occur on thylakoid membranes
• The carbon fixation reactions (formation of
carbohydrate) occur in the stroma
Biology, Sixth Edition
Chapter 8,
Conditions for photosynthesis
• Adequate supply of light
• Temperature affects the rate of
photosynthesis
– Proper temperature for photosynthesis varies
from plant to plant
• Lack of water will cause a plant to stop
photosynthesis
• Cell’s ability to absorb sufficient CO2
Classification of organisms according
to how they obtain energy
• Autotrophs
– “self-feeders” (producers) – organisms that
make their own food (photosynthesis)
– All green plants, certain bacterial and
protozoa
• Heterotrophs
– “other-feeders” (consumers) – organisms that
must obtain their nutrition from source
outside themselves
– Animals, humans, fungi, most bacteria
Engelmann’s Experiment: 1883
• Engemann sought to determine the wavelengths of light most
important for production of oxygen
• He illuminated a strand of Spyrogyra (a green alga) with the
spectrum of light from a prism while observing through a
microscope
• Aerobic bacteria were attracted to the regions of high oxygen
production: i.e. regions of photosynthesis
Aerobic bacteria
Biology, Sixth Edition
Chapter 8,
Absorption vs. Action Spectra
• Chlorophyll appears green because it absorbs most strongly in
the red and blue.
• The action spectrum is the result of the interaction of accessory
pigments with chlorophyll.
Absorption curves: chlorophylls a & b
Biology, Sixth Edition
Chapter 8,
The action spectrum of photosynthesis
Cellular Respiration
Cellular Respiration
• Glucose is produced during
photosynthesis and is used in cellular
respiration
• Cells need energy
– Cells obtain the needed energy by subjecting
glucose to a chemical process that is very
similar to burning
A Comparison of burning and
Cellular Respiration of sugar
• Both give off water and CO2
• Both require oxygen
• Both require activation energy
• As the glucose is “burned” the energy that
it contains is released for the use by the
cell, just as the burning of wood releases
heat energy
• This process of burning food to release
energy from it is called cellular
respiration
Cellular Respiration
• The breaking down of a food substance
into usable cellular energy in the form of
ATP
Aerobic Cellular Respiration
• Basically, cellular respiration is the
opposite of photosynthesis (they are not
the reverse of each other)
• Aerobic Cellular respiration breaks down
glucose to form water, carbon dioxide and
energy
Cellular Respiration Equation
C6H12O6 + 6 O2
6 CO2 + 6 H2O and energy
As a result of respiration, energy is released
from the chemical bonds found in complex
organic molecules (food).
Aerobic Cellular Respiration
enzymes
• Glucose + oxygen  ATP (energy) + water + carbon
dioxide
enzymes
• C6H12O6 + 6O2  38ATP + 6H2O + 6CO2
• Respiration takes stored chemical energy and
converts it to a ready-to-use chemical energy
(ATP)
Three phases of aerobic cellular
respiration
• Glycolysis
–
–
–
–
–
Requires an input of glucose and ATP
Breaks glucose into 2 smaller molecules
Takes place in the cytoplasm
Doesn’t require oxygen
Net gain of 2 ATP
• Citric Acid Cycle (Krebs Cycle)
– Produces 3CO2, and hydrogen
– Occurs in the mitochondria
– Net gain of 2 ATP
• Electron Transport Chain
–
–
–
–
Requires an input of hydrogen and oxygen
Occurs in the mitochondria
Forms water
Forms 34 ATP
Efficiency of cellular respiration
• Aerobic cellular respiration of glucose
traps approximately 50-60% of the energy
in the glucose molecule
– This breakdown of sugar is one of the most efficient
energy processes know
• Cars – only 20% of energy available in the
fuel is used, most of the rest radiates as
heat
Two types of cellular respiration
•Aerobic
Requires oxygen
•Anaerobic
Does not require
oxygen
Most cells carry on aerobic
cellular respiration
Some bacteria and fungi
All three Respiration steps
Glycolysis only
Anaerobic Cellular Respiration
• Some cells exist in environments that do
not have oxygen available
• Many bacteria in the lower layers of
swamps, lakes, or the ocean do not have
oxygen
• Cellular fermentation: the breakdown of
food (usually glucose) without oxygen
– Produces only 2 ATP
Fermentation
• Uses only Glycolysis.
• An incomplete oxidation - energy is still
left in the products
(alcohol or lactic acid).
• Does NOT require O2
• Produces ATP when O2 is not available.
Two Types of Cellular
Fermentation
• Lactic acid fermentation
– Formation of lactic acid from glucose
– Bacteria that form yogurt and cottage cheese
• Alcoholic fermentation
– The formation of alcohol and CO2 from
glucose
– Preformed by yeast cells (baking evaporates
the alcohol of bread dough and CO2 causes
dough to rise)
Lactic Acid Fermentation
• Done by human muscle cells under
oxygen debt.
• Lactic Acid is a toxin and causes soreness
and stiffness in muscles.
Strict vs. Facultative Respiration
• Strict - can only carry out Respiration one
way… aerobic or anaerobic.
• Facultative - can switch respiration types
depending on O2 availability. Ex - yeast
Importance of Respiration
• Alcohol Industry - almost every society
has a fermented beverage.
• Baking Industry - many breads use yeast
to provide bubbles to raise the dough.
Matching
Sugar Cane
Barley
Grapes
Juniper Cones
Agave Leaves
Rice
Potatoes
Gin
Saki
Tequila
Vodka
Beer
Wine
Rum
Comparing Photosynthesis and
Cellular respiration
• Photosynthesis
– Food accumulated
– Energy form sun
stored in glucose
– CO2 taken in
– O2 given off
– Goes on only in light
– Occurs only in
presence of
chlorophyll
• Cellular Respiration
– Food broken down
– Energy of glucose
released
– CO2 given off
– O2 taken in
– Goes on day and night
– Occurs in all living
cells