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Intro to Biology
Week 2
Energy in Cells, Capturing Energy
and Harvesting Energy –
Glycolysis,
and Cellular Respiration – Athletes.
Chapter 5
• Energy Flow in the Life of a Cell
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What Is Energy?
• From potential energy to kinetic energy
• Potential – energy not yet released
• Kinetic – energy in motion
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Potential Energy
Kinetic Energy
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Laws of Thermodynamics
First Law (Conservation of Energy)
Energy is neither created nor destroyed; it
is always conserved.
Second Law
Energy always tends to go from a more
usable form to a less usable form, so the
amount of energy available to do work
decreases (entropy occurs).
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Consequence Of Laws Of
Thermodynamics For Living
Organisms
Organisms require a constant input
of energy to maintain a high level of
organization.
“Feed Me Seymour!”
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This Slide is Yellow
Types of Energy Systems
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What Is Energy?
• Energy Cannot Be Created or Destroyed (1st
Law)
• Energy Tends to Become Distributed Evenly
(2nd Law)
• Matter Tends to Become Less Organized
(2nd Law)
• Living Things Use the Energy of Sunlight to
Create Low-Entropy Conditions
– We can see “opposite of entropy” flow when a
tremendous amount of energy is used…
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How Does Energy Flow in
Chemical Reactions?
• Exergonic reaction (p. 75)
• “Exit” – energy is released
• Sugar is burned in a flame or
consumed in the body, it reacts with
oxygen and produces CO2 and H2O +
energy
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Exergonic reaction
energy
released
reactants
products
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The other way…
• Endergonic reaction (p. 75)
• Takes in energy – saves it (“Engender”)
• CO2 + Water + energy = sugar and
oxygen
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Endergonic reaction
energy
used
products
reactants
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How Does Energy Flow in
Chemical Reactions?
• (Again) Exergonic Reactions Release
Energy
• The specifics: Burning glucose (sugar)
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Burning glucose
energy
released
glucose
oxygen
carbon
dioxide
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water
How Does Energy Flow in
Chemical Reactions?
• Endergonic Reactions Require an Input
of Energy
– The specifics:
• Photosynthesis (p. 76)
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Photosynthesis
energy
glucose
carbon
dioxide
water
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oxygen
How Does Energy Flow in
Chemical Reactions?
• Important Part: All Reactions Require
an Initial Input of Energy
– Things don’t burst into flame without some
kick – even exergonic ones
– Think of it as a blasting cap or fuse needed
to kick off the stick of dynamite
– Energy relations in exergonic and
endergonic reactions (p. 76)
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Burning glucose (sugar): an exergonic reaction
high
Photosynthesis: an endergonic reaction
high
activation energy needed
to ignite glucose
energy
content
of
molecules
glucose + O2
energy released
by burning glucose
energy
content
of
molecules
CO2 + H2O
low
activation
energy from
light captured
by photosynthesis
CO2 + H2O
low
progress of reaction
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progress of reaction
glucose
net energy
captured by
synthesizing
glucose
Burning glucose (sugar): an exergonic reaction
high
activation energy needed
to ignite glucose
energy
content
of
molecules
glucose + O2
energy released
by burning glucose
CO2 + H2O
low
progress of reaction
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Photosynthesis: an endergonic reaction
high
glucose
activation
energy from
light captured
by photosynthesis
energy
content
of
molecules
CO2 + H2O
low
progress of reaction
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net energy
captured by
synthesizing
glucose
How Does Energy Flow in
Chemical Reactions?
• Exergonic Reactions May Be Linked
with Endergonic Reactions
• Called a coupled reaction, the
exergonic reaction provides the input
energy needed for the endergonic
reaction:
• An ATP reaction creates energy
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How Is Energy Carried
between Coupled Reactions?
• ATP Is the Principal Energy Carrier in
Cells
adenosine triphosphate
– ATP synthesis: Energy is stored in ATP
– It is the ‘big one’ we will hear about again
and again
ENERGY IN!
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ATP synthesis: Energy is stored in ATP
energy
ATP
ADP
phosphate
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Energy Out
– ATP breakdown: Energy of ATP is released
(p. 77)
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ATP breakdown: Energy of ATP is released
energy
ATP
ADP
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phosphate
And things can get more
complex…
– A coupled reaction (p. 77) (first figure)
Storage and release processes can work
together to make the body work!
– Figure 5.4 Coupled reactions give off heat
(p. 78) (second figure)
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100 units
energy released
Exergonic reaction:
Endergonic reaction:
20 units
energy
relaxed
muscle
contracted
muscle
Coupled reaction:
80 units energy
released as heat
relaxed
muscle
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contracted
muscle
Coupled reaction: glucose breakdown and protein synthesis
glucose
exergonic
(glucose
breakdown)
protein
endergonic
(ATP synthesis)
exergonic
(ATP breakdown)
CO2 + H2O + heat
ADP +
net exergonic
“downhill” reaction
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heat
endergonic
(protein synthesis)
amino
acids
How Is Energy Carried
between Coupled Reactions?
• Subtitle- when complex reactions work
together…
• Electron Carriers Also Transport Energy
within Cells
– Electron carriers (p. 78)
– This is just to show you how things begin to build
from the microscopic up to the gigantic (your
muscles).
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Electron carrier molecules transport energy
exergonic
reaction
(energized
carrier)
(depleted
carrier)
net exergonic
“downhill” reaction
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endergonic
reaction
How Do Cells Control Their
Metabolic Reactions?
(or how to not have spontaneous
human combustion)
•
•
•
The cell is a tiny chemical factory. As it works,
this production of chemicals is called it’s
metabolism
Many chemical reactions linked together
make up a metabolic pathway
(next slide) Simplified view of metabolic
pathways (p. 79)
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Intermediates
Initial reactant
Final products
PATHWAY 1
enzyme 1
enzyme 2
enzyme 3
enzyme 4
PATHWAY 2
enzyme 5
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enzyme 6
How Do Cells Control Their
Metabolic Reactions?
• At Body Temperatures, Many
Spontaneous Reactions Proceed Too
Slowly to Sustain Life, something is
needed to make them happen easier…
• Catalysts Reduce Activation Energy
– Figure 5.7 Catalysts reduce activation
energy (p. 79)
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high
activation energy
without
catalyst
energy
content
of
molecules
activation energy
with catalyst
reactants
products
low
progress of reaction
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How Do Cells Control Their
Metabolic Reactions?
• Enzymes Are Biological Catalysts
(you’ve heard of enzymes before…
now you know what they do)
• The Structure of Enzymes Allows Them
to Catalyze Specific Reactions
– The cycle of enzyme-substrate interactions
(p. 80)
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substrates
active site
of enzyme
enzyme
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How Do Cells Control Their
Metabolic Reactions?
• The Activity of Enzymes Is Influenced
by Their Environment
• The 3-D structure (like proteins last
year)
• i.e. the salty brine in pickles keeps the
enzymes in bacteria working – so they
can’t attack and break down the
cucumbers.
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Chapter 6
• Capturing Solar Energy:
Photosynthesis
• Remember…sunlight is the source of
all (>99%)
• (look at solar spectra graph pg 88.)
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•
Everything from Gamma rays to Radio waves come out of the sun, but
we are most interested in the peak of this energy… which is in the
visible light portion of the electromagnetic spectrum
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What Is Photosynthesis?
• Photosynthesis Converts Carbon Dioxide
and Water to Glucose (simple sugars)
• Remember – trees/grass etc. are solidified
air…CO2 !
• Plant Photosynthesis Takes Place in Leaves
– Figure 6.1 An overview of photosynthetic
structures (p. 86)
– Stomata (stoma cingular) = holes or breathing
– mesophyll where photosynthesis occurs
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internal leaf structure
mesophyll
cells
stoma
chloroplasts
chloroplast in mesophyll cell
vein
outer membrane
inner membrane
thylakoid
stroma
channel
interconnecting
thylakoids
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internal leaf structure
mesophyll
cells
stoma
chloroplasts
vein
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chloroplast in mesophyll cell
outer membrane
inner membrane
thylakoid
stroma
channel
interconnecting
thylakoids
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What Is Photosynthesis?
• Leaf Cells Contain Chloroplasts – these are the organelles
in which photosynthesis occurs.
• Photosynthesis Consists of Light-Dependent and LightIndependent Reactions
– light dependent reactions – thylakoids capture sunlight energy and
convert some of it into chemical energy
• these molecules = ATP (adenosine triphosphate (ATP))
• and the electron carrier NADPH (nicotinamide adenine dinucleotide
phosphate)
• Oxygen is producted
– light independent reactions – enzymes in the stroma use the
chemical energy above to make glucose (sugars/starch) or other
organic molecules
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H2O
LIGHT-DEPENDENT
REACTIONS
(thylakoids)
depleted
carriers
(ADP, NADP+)
CO2 + H2O
O2
energized
carriers
(ATP, NADPH)
LIGHT-INDEPENDENT
REACTIONS
(stroma)
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glucose
How Is Light Energy
Converted to Chemical
Energy?
• Light, chloroplast pigments, and
photosynthesis (p. 88)
• (next image) Chlorophyll strongly absorbs
violet, blue and red light (reflects green looking green)
• Carotenoids absorb blue and green (reflects
orange looking orange –visible in the fall
when the leaves die, the green fades first)
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Visible light (“rainbow colors”)
Gamma rays
X-rays UV
Infrared
Visible light
Absorbance of photosynthetic pigments
carotenoids
chlorophyll
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Microwaves
Radio
waves
Visible light (“rainbow colors”)
Gamma rays
X-rays UV
Infrared
Visible light
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Microwaves
Radio
waves
Absorbance of photosynthetic pigments
carotenoids
chlorophyll
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How Is Light Energy
Converted to Chemical
Energy?
• Light Energy Is First Captured by Pigments
in Chloroplasts
• The Light-Dependent Reactions Generate
Energy-Carrier Molecules
– Light, chloroplast pigments, and photosynthesis
(p. 88)
– PS I= photosynthesis process 1
– PSII= photosynthesis process 2
– ETC = Electron Transport Chain
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thylakoids
chloroplast
within thylakoid membrane
PS II
ETC
reaction centers
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PS I
ETC
How Is Light Energy
Converted to Chemical
Energy?
– Photosystem II Generates ATP (one of our
energy carriers)
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Photosystems – away!
• Photosystem I Generates NADPH (another
one of our energy transport chemicals)
• Splitting Water Maintains the Flow of
Electrons through the Photosystems
(The electrons that move through the chemical
reactions have to be restored
somehow…water does it)
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energy level of electrons
sunlight
photosystem I
energy to drive
reaction
center
synthesis
photosystem
II
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How Is Chemical Energy
Stored in Glucose Molecules?
• So we have energy now… storage?
• Sugars! Starches! Glucose
• The Cycle Captures Carbon Dioxide
–
–
–
–
In through the stomata (breathing)
Figure 6.4 The C3 cycle of carbon fixation (p. 90)
The output is glucose!
Memorize? No just know it exists. It’s a cycle
that takes in CO2 and outputs glucose (C6H12O6)
• RuBP step = ribulose bisphospate
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6 H2O
6 CO2
6
12
RuBP
PGA
C3
cycle
12
12
6
12
12
6
G3P
glucose
(or other organic
compounds)
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12
What Is the Relationship
between Light-Dependent and
Light-Independent Reactions?
• Figure 6.5 Two sets of reactions are
connected in photosynthesis (p. 91)
• Photo = light capturing part
• Synthesis = light independent part 
glucose
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energy from
sunlight
Light-dependent
reactions occur
in thylakoids.
Lightindependent
reactions
(C3 cycle) occur
in stroma.
chloroplast
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glucose
CO2 in and out of the forest…
• Forests both consume and emit carbon
dioxide (p. 92)
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How Does the Need to
Conserve Water Affect
Photosynthesis?
•
•
•
•
•
Photosynthesis needs CO2
But too many pores = water loss!
So stomata can open and close
= Regulation!
But…When Stomata Are Closed to
Conserve Water, Wasteful Photorespiration
Occurs
– Figure 6.6 Comparison of C3 and C4 plants
(p. 93) RuBP step CAN use O2 when CO2 is not
available. Not good for glucose making!
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C3 and C4 Plant primer
• Named by which Carbon cycle they use
during photosynthesis.
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C3 plants use the C3 cycle
within chloroplast in mesophyll cell
CO2
O2
PGA
CO2
C3
CYCLE
RuBP
G3P
bundlesheath
cells
glucose
within chloroplast in mesophyll cell
C4 plants use the C4 pathway
CO2
PEP
4-carbon
molecule
C4
Pathway
pyruvate
bundlesheath
cells
CO2
O2
PGA
CO2
C3
CYCLE
RuBP
G3P
glucose
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within chloroplast in bundle-sheath cell
within chloroplast in mesophyll cell
C3 plants use the C3 cycle
CO2
O2
PGA
CO2
C3
CYCLE
G3P
glucose
bundlesheath
cells
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RuBP
C4 plants use the C4 pathway
within chloroplast in mesophyll cell
CO2
PEP
4-carbon
molecule
C4
Pathway
pyruvate
CO2
bundlesheath
cells
O2
PGA
CO2
C3
CYCLE
RuBP
G3P
glucose
within chloroplast in bundle-sheath cell
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How Does the Need to Conserve
Water Affect Photosynthesis?
• An Alternative Pathway Reduces
Photorespiration in Plants
• C3 and C4 Plants Are Each Adapted to
Different Environmental Conditions
• During warm dry weather can make plants
open their stoma but not be able to capture
enough energy to live.
• C3 best in low light high water environments
(pole-ward forests) and C4 abundant light but
water is scarce (deserts)
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Chapter 7
Show me the glucose!
• Harvesting Energy: Glycolysis and
Cellular Respiration
• To power chemical reactions in the cell,
the most common energy-carrier is ATP
(adenosine triphosphate).
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What Is the Source of a Cell’s
Energy?
• Glucose Is a Key Energy-Storage Molecule
(other chemicals work, but glucose it’s the
main player)
• Photosynthesis Is the Ultimate Source of
Cellular Energy
• Glucose Metabolism and Photosynthesis Are
Complementary Processes
– Energy+water+carbon dioxide  glucose +
oxygen Photosynthesis
– glucose + oxygen  energy + water + carbon
dioxide Glucose Metabolism
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How Do Cells Harvest Energy
from Glucose?
• An overview of glucose metabolism
(p. 101)
• Step 1 = Glycolysis (w/ or w/o oxygen) makes
pyruvate (releases chemical energy -ATP)
• Step 2 = Cellular respiration (w/oxygen)
or
Fermentation (w/o oxygen)
• Step 3 = w/oxygen pyruvate enters the
mitochondria  CO2 and water + lots of ATP
w/o oxygen, doesn’t enter the mitochondria and
is made into lactate or ethanol and no ATP
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(cytoplasm)
glucose
2
Glycolysis
2
2
lactate
or
pyruvate
2
2
Fermentation
ethanol
2 CO2
CO2
Cellular respiration
4
2 acetyl CoA
Krebs
cycle
CO2
2
electron
carriers
Electron
transport chain
32 or 34
H2O
(mitochondrion)
O2
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intermembrane
compartment
What Happens During
Glycolysis?
• The essentials of glycolysis (p. 101)
• Glycolysis makes only 2 ATP (energy
transporters) and two NADH (energy
transporters using the electron carrier)
(NADH = nicotinamide adenine dinucleotide)
• (The next image is a expansion of Step
1 above)
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2
2
4
4
2
2
G3P
glucose
pyruvate
fructose
bisphosphate
2
1 Glucose activation
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2
2 Energy harvest
7.3 What Happens During
Glycolysis?
• Activation Consumes Energy
– The first part of the reaction
• Energy Harvest Yields Energy-Carrier
Molecules
– The second part of the reaction
– Essential for life
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What Happens During
Cellular Respiration?
• Cellular respiration (p. 103) Step 2 above.
• When you break it down… it is a bit
complex
• Look for the parts you recognize…
• (Follow 1  8)
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mitochondrion
inner
membrane
intermembrane
compartment
outer
membrane
matrix
glucose
cristae
Glycolysis
1
2 pyruvate
coenzyme A
(intermembrane
compartment)
2
H+
acetyl CoA
8
(cytoplasm)
CO2
7
6
H+
H+
Krebs
cycle
H+
5
(inner membrane)
H2O
1/2 O
H+
–
H+
H+
2e
2 H+
4
H+
–
Electron
2e
transport
chain
(outer membrane)
3
energized
electron
carriers
depleted carriers
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(matrix)
CO2
What Happens During
Cellular Respiration?
• The Krebs Cycle Breaks Down
Pyruvate (from Step 1) in the
Mitochondrial Matrix
– The reactions in the mitochondrial matrix
(p. 104)
– The Krebs cycle is also called the citricacid cycle since citrate is formed first…
– (More detail than we’ll quiz on)
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3
1 Formation of
acetyl CoA
coenzyme A
pyruvate
3
CO2
coenzyme A
acetyl CoA
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2 Krebs
cycle
2
CO2
What Happens During
Cellular Respiration?
• Energetic Electrons Are Carried to
Electron Transport Chains
– Table 7.1 Summary of Glycolysis and
Cellular Respiration (p. 105)
– Remember, we are looking for ways to
make the life important energy transporters
– Figure 7.5 The electron transport chain in
the inner mitochondrial membrane (p. 104)
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(matrix)
3
1/2 O2 + 2H+
2e–
1
2e–
H2O
electron
carriers
(inner
membrane)
H+
2
energy to drive
(intermembrane compartment)
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H+
synthesis
H+
What Happens During
Cellular Respiration?
• Notice that there is Hydrogen (freed
from the water) moving out at different
steps of this respiration process (image
back a slide)
• The cell gets more energy from a
Hydrogen-Ion Gradient which Is Used
to Produce yet more ATP
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What Happens During
Fermentation?
• We don’t have oxygen (or enough
oxygen) present.
• Some Cells Ferment Pyruvate to Form
Alcohol (woo hoo)
– Glycolysis followed by alcoholic
fermentation (p. 106)
– Don’t get enough oxygen (in bread for
instance) and you get Fermentation (p.
107) byproducts
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Glycolysis followed by
alcoholic fermentation
regeneration
glucose
2
2
(glycolysis)
2
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2
(fermentation)
ethanol
pyruvate
2
CO2
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What Happens During
Fermentation?
• Other Cells Ferment Pyruvate to
Lactate
– You also get lactic acid as a byproduct
– Glycolysis followed by lactate fermentation
(p. 106)
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Glycolysis followed by
lactate fermentation
regeneration
2
2
(glycolysis)
glucose
2
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(fermentation)
pyruvate
2
lactate
Next time…
• Chapters 8,9,10,11,12
•
•
•
•
•
DNA
Gene expression and regulation
How cells reproduce
Patterns of Inheritance
Biotechnology
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