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Bio 211
Day 10
Today
• How Do Cells Obtain Energy?
• What Happens During Glycolysis?
• What Happens During Cellular Respiration?
• What Happens During Fermentation?
• How does photosynthesis work?
Participation
• Tell me everything you know about photosynthesis…
• Compare with a friend
Figure 8-1 Photosynthesis provides the energy released during glycolysis and cellular respiration
energy from sunlight
Most of life could
be summarized as:
Creating sugar
And then
Oxidizing sugar
photosynthesis
6 CO2
6 H2O
6 O2
cellular
respiration
C6H12O6
glycolysis
ATP
Breaking down glucose is photosynthesis
backwards
Photosynthesis
6 CO2  6 H2O  light energy  C6H12O6  6 O2
Complete glucose breakdown
C6H12O6  6 O2  6 CO2  6 H2O  ATP  heat
(cytosol)
A respiration summary
1 glucose
Glycolysis
glycolysis
Glucose (6C)  3GP  2x pyruvate (3C)
ATP
2 lactate
fermentation
2 pyruvate
If O2 is available
If no O2 is available
2 ethanol

2 CO2
6 O2
2C + 4C  4C  CO2 & electrons on
NADH
Electron transport chain
electron transfer  O2  H2O
proton gradient used to make ATP
requires ATP synthase
Photosynthesis summary
cellular
respiration
6 CO2
Kreb’s cycle
Light reactions – pigments, ETCs
ATP
H2O split by photons  O2 + electrons
high energy electron transfer  NADPH
proton gradient used to make ATP
requires ATP synthase
6 H2O
Dark reactions – “Calvin cycle”
CO2  3C G3P glucose
mitochondrion
Let’s review glycolysis
• Which of these goes in and which comes out?
• ATP
• NADH
• NAD+
• Glucose
• pyruvate
Let’s review glycolysis
• INPUT vs OUTPUT
• ATP
• NADH
• NAD+
- reduced to NADH
• Glucose - oxidized
• pyruvate
One more thing… G3P
The essentials of glycolysis
Fig. 8-3
Figure 8-4 A mitochondrion
LABEL ME!!
Figure 8-4 A mitochondrion
matrix
inner membrane
intermembrane space
outer membrane
Figure 8-5 Reactions in the mitochondrial matrix
Formation of
acetyl CoA
coenzyme A
3 NADH
3 NAD
CO2
FADH2
coenzyme A
acetyl CoA
pyruvate
NAD
FAD
Krebs
cycle
NADH
ADP
ATP
Krebs cycle
• acetyl CoA + 4C molecule  6C citrate coenzyme A is released –
where does it go?
• Series of enzymes 2C acetyl 2 CO2
• 4C molecule is regenerated
Where do the electrons go next?
Where do the carriers drop their cargo?
• NADH
• FADH2
Electron transport chain: proton pumps
Per NADH, protons are in 3 places
Per FAD, protons pumped in 2 places
Figure 5.16
Chemiosmosis
Proton flow through ATP synthase turns its
turbine; mechanical energy used to power
ATP synthesis from ADP and Pi
Figure 5.15
1. Do prokaryotes (bacteria) perform cellular
respiration?
YES… and BTW why should we care?
Because of ecology, medicine, industry, science
Diagram of aerobic respiration
• Draw a eukaryotic cell with a mitochondrion
• Where are
• Glycolysis
• Kreb’s cycle
• Electron transport chain
Where do these reactions happen?
Pathway
Glycolysis
Intermediate step
Krebs cycle
ETC
Eukaryote
Prokaryote
Where do these reactions happen?
Pathway
Eukaryote
Prokaryote
Glycolysis
cytoplasm
Cytoplasm
Intermediate step
Mitochondrial matrix
Cytoplasm
Krebs cycle
Mitochondrial matrix
Cytoplasm
ETC
Inner mitochondrial membrane
Plasma membrane
2. What if there is no oxygen?
• Typical textbook says:
• Without oxygen, electrons stop moving through ETC, H is
not pumped across the inner membrane
• The H gradient dissipates, and ATP synthesis by
chemiosmosis stops
• ATP generation continues only when there is a steady
supply of oxygen
• Is this true?
• This is true in most tissues in our bodies but NOT in all
living things… some bacteria
Two anaerobic processes
• Anaerobic respiration
• Fermentation
• Are they the same thing??
Can prokaryotes do respiration?
• Yes some of them can!
• Some do aerobic respiration
• Some do anaerobic respiration
• WAIT… but do they have mitochondria??
Respiration by cell type
• Eukaryotes
• Where is the ETC?
• Which part of mitochondrion is acidic
• How much ATP per glucose?
• Prokaryotes
•
•
•
•
Where is the ETC?
Where do the protons go?
How much ATP per glucose?
Why is it more?
Respiration by cell type
• Eukaryotes
• Where is the ETC? Inner mito membrane
• Which part of mitochondrion is acidic? Intermembrane
space
• How much ATP per glucose? Textbooks 32-36
• Prokaryotes
•
•
•
•
Where is the ETC?
Where do the protons go?
How much ATP per glucose? 34-38
Why is it more?
Chapter 7
Photosynthesis
What is photosynthesis?
Capturing solar energy
used for?
Making sugar!!
What is the energy
Figure 8-1 Photosynthesis provides the energy released during glycolysis and cellular respiration
energy from sunlight
Most of life could
be summarized as:
Creating sugar
And then
Oxidizing sugar
photosynthesis
6 CO2
6 H2O
6 O2
cellular
respiration
C6H12O6
glycolysis
ATP
Chapter 7 topics
• What Is Photosynthesis?
• How is light energy converted to chemical energy? (the
“light reactions”)
• How is chemical energy stored in sugar?
(Calvin
cycle aka “dark reactions”)
What Is Photosynthesis?
• For most organisms, energy is derived from sunlight, either directly or
indirectly
• DIRECT: Trap sunlight using photosynthesis
• Photosynthesis - solar energy is converted to chemical energy –
trapped and stored in the bonds of sugar
• INDIRECT: Organisms that cannot directly trap sunlight get their
energy from where?
Special equipment – the solar panel
• Leaves are structures adapted for photosynthesis
• Photosynthesis in plants takes place in chlorophyll-containing organelle, the
_______,usually in leaf cells
• Chloroplasts perform chemical reactions to convert energy from ________
into stored energy in sugar
• Will all parts of a plant contain chloroplasts?
Figure 7-1 An overview of photosynthetic structures
cuticle
upper
epidermis
mesophyll
cells
Leaves
stoma
stoma
bundle sheath cells
vascular bundle (vein)
outer membrane
inner membrane
thylakoid
stroma
Chloroplast
lower
epidermis
chloroplasts
Internal leaf structure
channel
interconnecting
thylakoids
Mesophyll cell containing chloroplasts
Leaf surface anatomy
• Epidermis
• upper and lower surfaces of a leaf consist of a layer of transparent cells,
the epidermis
• Cuticle
• The outer surface of both epidermal layers is covered by a
transparent, waxy, waterproof layer to reduce the evaporation
of water from the leaf
• Stomata/stoma
• Leaves obtain CO2 for photosynthesis from the air through
pores in the epidermis called stomata (stoma)
Figure 7-2 Stomata
Stomata open
Stomata closed
Figure 7-1 An overview of photosynthetic structures
A
B
mesophyll
cells
Leaves
stoma
C
D
outer membrane
inner membrane
thylakoid
stroma
Chloroplast
chloroplasts
bundle sheath cells
vascular bundle (vein)
Internal leaf structure
channel
interconnecting
thylakoids
Mesophyll cell containing chloroplasts
Inside the leaf
• Mesophyll
• layers of cells inside the leaf where the chloroplasts are located and
photosynthesis occurs
• Chloroplasts
• Where _______ takes place in plants - most of these organelles are found in
mesophyll cells
Figure 7-1 An overview of photosynthetic structures
cuticle
upper
epidermis
A
Leaves
stoma
stoma
bundle sheath cells
vascular bundle (vein)
outer membrane
inner membrane
thylakoid
stroma
B
lower
epidermis
chloroplasts
Internal leaf structure
channel
interconnecting
thylakoids
Mesophyll cell containing chloroplasts
Chloroplast anatomy
• double membrane enclosing a fluid called stroma
• Embedded in the stroma are disk-shaped membranous sacs called
thylakoids
• The “light reactions” of photosynthesis occur in and adjacent to the
membranes of the thylakoids
• The “dark reactions” – Calvin cycle – take place in the stroma
photosynthesis
• Starting with carbon dioxide (CO2) and water (H2O), photosynthesis converts
sunlight energy into chemical energy stored in bonds of glucose and releases
oxygen (O2) as a product by the following equation:
6 CO2  6 H2O  light energy  C6H12O6  6O2
carbon
water
sunlight
glucose
oxygen
dioxide
(sugar)
Does this entire process require sunlight?
What are the “light” reactions? And the “dark”?
Light vs dark – how are they related?
Figure 7-3 An overview of the relationship between the light reactions and the Calvin cycle
H2O
6
6
CO2
energy from
sunlight
ATP
light
reactions
NADPH
Calvin
cycle
ADP
NADP
thylakoid
sugar
(stroma)
chloroplast
O2
C6H12O6
Light reactions
• light reactions: chlorophyll and other molecules embedded in the
chloroplast thylakoid membranes capture sunlight energy and convert
some of it into chemical energy stored in the energy-carrier molecules
ATP and NADPH
Calvin cycle
• In the reactions of the Calvin cycle, enzymes in the stroma use CO2
from the air and chemical energy from the energy-carrier molecules
to synthesize a three-carbon sugar that will be used to make glucose
Photosynthesis is the sum of BOTH light and
dark reactions
• The “photo” part of photosynthesis refers to the capture of sunlight
in the thylakoid membranes
• The “synthesis” part of photosynthesis refers to the Calvin cycle,
which synthesizes sugar from the energy captured in ATP and NADPH
in the light reactions
How Is Light Energy Converted to Chemical
Energy?
• Convert energy of sunlight to chemical energy in ATP
and NADPH
• Light reaction machinery is anchored within the
membranes of the thylakoid
What is light?
• The sun emits energy
• a broad spectrum of electromagnetic radiation
• This electromagnetic spectrum ranges from
waves, to infrared, visible, UV, & gamma rays
--------- short)
• Wavelength of light
• inversely related to strength
• Long wavelength (radio) versus short wavelength (gamma)
radio
(long ------------------------
Electromagnetic (EM) spectrum
Capturing light with pigments
• Light is made of photons
• individual packets of energy
• Wavelength of light
• Size inversely related to strength
• Gamma rays are ____ so that makes them strong/weak?
• radio waves are big/small? so they are _____
• Visible light
• Wavelength strong enough to alter pigment – eg. chlorophyll a
• Chlorophyll a
• Main light-capturing pigment in chloroplasts
• absorbs violet, blue, and red light
• Green light is reflected, which is why leaves appear green
Is chlorophyll alone?
• accessory pigments in chloroplasts
• absorb more wavelengths of light and transfer them to
chlorophyll a
• Chlorophyll b
• absorbs blue and red-orange wavelengths of light
(missed by chlorophyll a)
• Carotenoids
• absorb blue and green light, and appear yellow or orange to
our eyes bc they reflect these colors
• Why do the leaves turn??
• In autumn, green chlorophyll breaks down before the
carotenoids do, revealing their yellow color
Figure 7-4 Light and chloroplast pigments
light absorption (percent)
100
chlorophyll b
80
carotenoids
60
chlorophyll a
40
20
0
wavelength (nanometers)
400
450
gamma rays
500
550
600
visible light
X-rays UV
higher energy
650
700
750
micro- radio
infrared waves waves
lower energy
Figure 7-5 Loss of chlorophyll reveals carotenoid pigments
Where do the light reactions happen?
• In association with the thylakoid membranes
• The thylakoid contain photosystems,
• a cluster of chlorophyll and accessory pigment molecules
surrounded by various proteins
• Two photosystems
• photosystem II (PS II) and photosystem I (PS I), work together
during the light reactions
Light reactions – the machinery
• Each photosystem has a unique electron transport chain nearby
embedded in the thylakoid membrane
• Within the thylakoid membrane, electron path is:
PS II  ETC II  PS I  ETC I  NADP
Light reactions – absorbing light
The reaction center within each photosystem consists of a pair of
specialized chlorophyll a molecules and a primary electron acceptor
molecule embedded in a complex of proteins
1. Photons of light are absorbed by pigment in photosystem II --> electrons are
energized
2. The energized electron is ejected from the chlorophyll and recaptured by the
primary electron acceptor
Light reactions – creating a gradient
Photosystem II uses light energy to create a hydrogen ion gradient and
split water
3. The electron from PS II is passed down the ETC losing energy at each step
4. This energy is used to pump hydrogen ions (H) across the thylakoid
membrane into thylakoid space, where it will be used to generate ATP (see
later)
Light reactions – two photosystems
Photosystem I is actually the second system
5. The energy-depleted electron leaves ETC II and enters the reaction center of PS
I, where it replaces an electron ejected when light strikes photosystem I
6. Light energy striking PS I is captured by its pigment molecules and funneled to
a chlorophyll a molecule in the reaction center
7. This ejects an energized electron that is picked up by the primary electron
acceptor of PS I
Light reactions gradient
Photosystem I also has a ETC
8. From the primary electron acceptor of PS I, the energized electron is passed
along ETC I until it reaches NADP
9. The energy-carrier molecule NADPH is formed when each NADP molecule
picks up two energetic electrons, along with one hydrogen ion
Animation: Photosynthesis—Light-Dependent
Figure 7-6 Energy transfer and the light reactions of photosynthesis
H2O
CO2
ATP
light
reactions
Calvin
cycle
NADPH
ADP
NADP
sugar
O2
C6H12O6
high
e
electron
transport
chain I
e
e
primary
electron
acceptor
NADPH
NADP
energy level of electrons
e
e
light
energy
electron
transport
chain II
pigment
molecules
e
ATP
reaction center
chlorophyll a molecules
Photosystem II
e
low
2 H
H2O
½
O2
Photosystem I
H
OK so why did we make a gradient?
• The H+ gradient generates ATP by chemiosmosis
Chemiosmosis???
• three steps
1. As the energized electron travels along ETC, the energy it loses is used to pump hydrogen
ions into the thylakoid space
2. High concentration H inside the space relative to the surrounding stroma creates a
gradient
Where do the H+ ions want to go? Can they?
3. H flows down its concentration gradient through a thylakoid channel protein called ATP
synthase, generating ATP from ADP
Figure 7-7 Events of the light reactions occur in and near the thylakoid membrane
thylakoid
chloroplast
(stroma)
light
energy
CO2
H is pumped into
the thylakoid space
H
electron
transport
chain I
electron transport chain II
e
H
e
Calvin
cycle
NADP
NADPH
sugar
e
e
C6H12O6
ATP
synthase
e
ADP
e
photosystem II
2 H
H2O
½
(thylakoid space)
O2
H
Pi
photosystem I
H
H
H
H
H
A high H concentration is
created in the thylakoid space
H
H
thylakoid
membrane
The flow of H down
its concentration gradient
powers ATP synthesis
ATP
Bio 211
D10 part 2
So we got through the “light reactions” –
what’s next?
• Let’s finish photosynthesis! – DARK REACTIONS – “Calvin cycle”
The Calvin Cycle:
how is ATP used to make sugar?
• Starting material:
• what’s in sugar? how do we get those atoms?
• Carbon dioxide and water  sugar
• What kind of reaction is this?
• Where does the energy come from?
• Where does this happen?
The Calvin Cycle:
how is ATP used to make sugar?
• Starting material:
• what’s in sugar? how do we get those atoms?
• Carbon dioxide and water  sugar
• What kind of reaction is this?
• Where does the energy come from?
• ATP and NADPH synthesized from light reactions are used to power the
synthesis of a simple sugar (gyceraldehyde-3-phosphate, or G3P)
• Where does this happen?
• This is accomplished through a series of reactions occurring in the stroma
called the Calvin cycle
Steps in the Calvin cycle
• Three steps
1. Carbon fixation
2. The synthesis of G3P
3. The regeneration of ribulose bisphosphate (RuBP)
Figure 7-9 The Calvin cycle fixes carbon from CO2 and produces the simple sugar G3P
H2O
CO2
ATP
light
reactions
Calvin
cycle
NADPH
ADP
NADP
sugar
O2
C6H12O6
Carbon fixation
combines three CO2
with three RuBP using
the enzyme rubisco
3
CO2
6
3
PGA
RuBP
Calvin
cycle
3
6
ATP
6
ADP
ADP
6 NADPH
3
ATP
6 NADP
5
6
G3P
Using the energy
from ATP, the five
remaining molecules
of G3P are converted
to three molecules
of RuBP
G3P
Energy from ATP
and NADPH is used
to convert the six
molecules of PGA to
six molecules of G3P
1
G3P
One molecule of
G3P leaves the cycle
1
1
G3P
Two molecules of G3P combine
to form glucose and other molecules
1
G3P
glucose
Let’s walk through them shall we?
• Three steps
1. Carbon fixation
2. The synthesis of G3P
3. The regeneration of ribulose bisphosphate (RuBP)
Step one: carbon fixation
1. Carbon fixation
• CO2 is incorporated, or “fixed,” into a larger organic molecule
• enzyme rubisco combines three CO2 molecules with three RuBP
(ribulose bisphosphate) molecules, forming three unstable 6carbon molecules that each quickly split in half
• Six molecules of a 3-carbon product, phosphoglyceric acid (PGA),
result
• Making 3-carbon PGA molecule is called the C3 pathway
Step two: G3P synthesis
2. Uses energy of ATP and NADPH (generated by light reactions)
• Converts six PGA molecules into six of the 3-carbon sugar molecule G3P
(glyceraldehyde 3 phosphate)
Step three: RuBP
3. The regeneration of RuBP
• ATP from the light reactions is used with five of the six G3P molecules
formed to regenerate the 5-carbon RuBP necessary to repeat the cycle
• The remaining G3P molecule, which is the end product of photosynthesis,
exits the cycle
Animation: Light-Independent Reactions
Figure 7-9 The Calvin cycle fixes carbon from CO2 and produces the simple sugar G3P
H2O
CO2
ATP
light
reactions
Calvin
cycle
NADPH
ADP
NADP
sugar
O2
C6H12O6
Carbon fixation
combines three CO2
with three RuBP using
the enzyme rubisco
3
CO2
6
3
PGA
RuBP
Calvin
cycle
3
6
ATP
6
ADP
ADP
6 NADPH
3
ATP
6 NADP
5
6
G3P
Using the energy
from ATP, the five
remaining molecules
of G3P are converted
to three molecules
of RuBP
G3P
Energy from ATP
and NADPH is used
to convert the six
molecules of PGA to
six molecules of G3P
1
G3P
One molecule of
G3P leaves the cycle
1
1
G3P
Two molecules of G3P combine
to form glucose and other molecules
1
G3P
glucose
Alternative pathways
• Some plants use other pathways for carbon fixation –
why?
• When plant stomata are closed in hot environments to prevent
water loss, oxygen builds up in the plant cells and RuBP
combines with it, rather than CO2, in a wasteful process called
photorespiration
• This process prevents the Calvin cycle from synthesizing sugar,
and plants may die under these circumstances
C4 and CAM
• When the Calvin cycle won’t work…
• Flowering plants have evolved two different mechanisms to circumvent
wasteful photorespiration
• The C4 pathway
• Crassulacean acid metabolism (CAM)
Figure E7-1 The C4 pathway and the CAM pathway
day
night
CO2
mesophyll
cell
PEP
(3C)
PEP
carboxylase
oxaloacetate
(4C)
pyruvate
(3C)
PEP
(3C)
PEP
carboxylase
malate
(4C)
pyruvate
(3C)
malate
(4C)
CO2
oxaloacetate
(4C)
mesophyll
cell
pyruvate
(3C)
rubisco
Calvin
cycle
malate
(4C)
CO2
sugar
rubisco
bundle
sheath
cell
C4 plants
CO2
malic acid
(4C)
Calvin
cycle
sugar
central vacuole
CAM plants
malate
(4C)
Last but not least
• Do we have glucose yet?
• In reactions that occur outside the Calvin cycle, what happens
next?
• What do plants do with all that glucose?
Last but not least
• Do we have glucose yet?
• We’ve got a bunch of G3P
• In reactions that occur outside the Calvin cycle,
• two G3P (3-C) can be combined to form glucose (6-C)
• What do plants do with all that glucose?
• Convert to a disaccharide eg. ________(a storage molecule) or
______(a major component of plant cell walls)
• Some glucose molecules are broken down in _______ ___________
to give the plant’s cells energy
Compare photosynthesis with respiration
• What process requires O2 as a reagent?
• A – photosynthesis
B – respiration
C-both
• Why?
• What process requires CO2 as a reagent?
• A – photosynthesis
B – respiration
C-both
D-neither
B – respiration
C-both
D-neither
B – respiration
C-both
D-neither
C-both
D-neither
• What process generates O2 ?
• A – photosynthesis
• CO2 ?
• A – photosynthesis
D-neither
• What process generates ATP?
• A – photosynthesis
B – respiration
• What process uses an electron transport chain?
• A – photosynthesis
B – respiration
C-both
D-neither
A few more questions
• What reactions MUST take place in the light?
•
•
•
•
A – conversion of sunlight to ATP
B – conversion of ATP to sugar
C – both A and B
D – none of the above
• Do the dark reactions REQUIRE it to be dark?
• A – yes
B - no
• Are plants the only photosynthesizers?
• A – yes
B - no
• Do plants have mitochondria?
• A – yes
B - no
Drawings!
• Light reactions – what goes in, what comes out
• Light reactions – trace the path of the electron
• Dark reactions – what goes in, what comes out
• Compare mitochondrial structure to chloroplast structure
• Compare respiration to photosynthesis – focus on water and O2
• Compare respiration to photosynthesis – focus on CO2