Energy Flow:
Photosynthesis &
Cellular
Respiration
Functions of ATP
• Chemical work – synthesizing compounds
• Transport work – moving substances across
the plasma membrane
• Mechanical work – moving cell structures and
cells
•Energy coupling: use of
an exergonic process to
drive and endergonic
process
•ATP mediates most
energy coupling in cells
ATP
• Consist of
– a sugar
called ribose
– N containing
Adenine
– Three
phosphate
groups

Unstable w/3 PO4• All negative charge-repel each other


ADP is more stable
A change from a less stable molecule
to a more stable molecule releases
energy.
Covalent
Bonds
•
The energy can then be used to
drive other reactions (energy
coupling)
– ATP “carries” Energy
The structure and hydrolysis of ATP
All are negatively charged –
crowded and repel, creating
instability
When bonds are broken
from ATP to ADP
(hydrolysis).
The ATP cycle
ATP is a renewable resource that can be regenerated…
FAST – working muscle cell recycles its
entire ATP pool once each minute;
-Turnover represents 10 million molecules of ATP
generated per second in a cell.
• Process by
which plants and
other organisms
use sunlight,
CO2 & H20 to
produce high
energy
carbohydrates
such as sugars
and starches.
• Prokaryotesphotosynthetic
capability is
present within
five major
groups of
bacteria.
Where
Photosynth
esis Occurs
The Internal Structure of a Leaf
Section 23-4
CO2 enters
through the
stomata
Epidermis
Chloroplasts
Stomata
Guard
cells
• Chloroplasts are only found in photosynthetic,
eukaryotic cells.
–
Chloroplasts are capable of harnessing energy from the sun's rays of light.
•Using this
energy from
the sunlight,
chloroplasts
are able to
form ATP as
well as
synthesizing
sugars from
water and
carbon dioxide.
Things to know about Chloroplasts
1. have a double membrane
2. have their own DNA (carries the
make enzymes)
info to
3. have their own ribosomes (more like the
ribosomes of prokaryotes) -used to synthesize
proteins
4. make their own enzymes required for
photosynthesis
5. require CO2 and H2O produce C6H12O6
6. contain chlorophyll (green chemical "traps"
sunlight energy)
Now let’s look at structure…
• The chloroplast is made up of 3 types of
membranes:
1. A smooth outer membrane which is freely
permeable to molecules.
2.A smooth inner membrane which contains many
transporters
3.A system of thylakoid membranes
Light and Pigments
In addition to water and carbon dioxide,
photosynthesis requires light. Light energy is
absorbed by the pigment CHLOROPHYLL and other
accessory pigments.
Pigments are
molecules
that absorb
light energy
Accessory Pigments
• Other pigments that trap other wavelengths -found in chromoplasts
– Capture light and pass the energy along to chlorophyll A.
• Ex. Carotenoids
* xanthophyll – yellows
* beta carotene – oranges
– These are masked by presence of chlorophylls, except in
autumn (when leaf cells stop synthesizing chlorophyll) –
“fall colors”
– Also is very obvious in “ripe” fruits, veggies
Ex. Apple, tomato
Sunlight is a mixture of many different
wavelengths…
(light energy is measured in
units called photons)
ROYGBIV
(vibgyor)
Pigments
• Substances in organisms that can absorb light.
• The color that you see is the one being REFLECTED
• CHLOROPHYLL is the major photosynthetic
pigment in plants
• 2 types: chlorophyll a – directly involved in
transformation of photons to
chemical energy
chlorophyll b – helps trap other wavelengths
and transfers it to chlorophyll a
Accessory Pigments
•Chlorophylls (green) and carotenoids (yellow, orange and red.)
Chlorophyll A and B Absorption
Spectrum
b
a
action spectrum and the absorption spectra
Location and structure of chlorophyll molecule
Photosystem
The pigment molecules have a
large head section that is
exposed to light in the surface
of the membrane; the
hydrocarbon tail anchors the
pigment molecules into the lipid
bilayer.
Double bonds
are the source
of the e- that
flow through
the ETC
Where is the
chlorophyll located?
Photosystems
• Chlorophyll molecules
are located in
photosystems.
– light-harvesting
complexes in the
thylakoid membranes.
Photosystem Structure:
1-Protein
2-Reaction Center
contains chlorophyll A and
several antenna pigments.
• Two PS:
– PS I and PS II
– PS II acts BEFORE PS
I ……..go figure...
PS II
680nm range
Also referred to as P680.
antenna
pigments are
predominantly
chlorophyll b,
xanthophylls, &
carotenoids
PSI
700nm range
Also referred to as P700
Now that you know all of
that……let’s actually
look at the process of
photosynthesis
Mr. Anderson’s Photosynthesis
Photosynthesis: Quick Overview
STAGE 1
STAGE 1: LIGHT DEPENDENT
REACTIONS
STEP 1: PS I (P700) and PS II (P680)
capture energy from sunlight.
Photosynthesis: Quick Overview
STAGE 1
-Water is Split
(photolysis) into
H+, Electrons, O2
-O2 diffuses out
of the
Chloroplasts
(Byproduct).
-Light Energy is
Converted to
Chemical Energy,
which is temp.
stored in ATP
and NADPH.
Photosynthesis: Quick Overview
Step 2
-ATP and
NADPH from
Step 1,
along with
CO2, is
converted to
glucose in
the Calvin
Cycle
STAGE 1
STAGE 2
Light Independent
Reaction

Light Dependent
Reaction

Steps of Light Dependent Reaction
1.
(Noncyclic Photophosphorylation)
PSII absorbs energy.
1.
2.
3.
4.
5.
2.
•
•
e- from double bonds in the head of ChloroA become energized and move to a
higher energy level. They are captured by a primary electron acceptor.
Photolysis: H2O gets split apart into 2 e- , 2 H+, and one oxygen atom.. The
e- replace those lost by ChloroA.
2 oxygen molecules combine and is released into the air.
H+ are released into the inner thylakoid space, which creates a higher [ H+ ]
inside the thylokoid.
e- from ChloroA are passes along a ETC consisting of plastoquinone (PQ)--complex of 2 cytochromes and several other proteins.
This flow is exergonic and provided energy to produce ATP by chemiosmosis. (photophosphorylation)
The ATP is used to power the Light Independent Reaction (Calvin Cycle)….this is a coupled reaction!
The e- end up at PS I.
1.
2.
3.
4.
5.
6.
PS I absorbs energy.
e- from double bonds in the head of ChloroA become energized and move to a
higher energy level. They are captured by a primary electron acceptor.
E- that are lost are replaced by the e- from PSII (step7).
e- from ChloroA are passes along a ETC – consisting of ferrodoxin.
NADPH is produced.
NADP in the stroma pick up 2 H+ and form NADPH and enter the calvin cycle.
Clip
Photosynthesis:
Light Dependent Reaction Overview
Overview clip
The light reactions and chemiosmosis: organization of the thylakoid membrane
The production of ATP using the energy of
sunlight is called photophosphorylation.
NADP=Nicotinamide
adenine dinucleotide
phosphate
P700
P680
Photolysis
H+
H+
H+
H+
H+ H+ H+
H+
+
H+ H
H+
“Chemiosmosis”
Animation
Chemiosmosis
“Chemiosmotic Theory”
-Peter Mitchell -1961
• Energy coupling
mechanism.
– Uses potential
energy stored
in the form of
a proton
gradient to
phosphorylate
ADP to
produce ATP.
ATP synthase-The Movie
Chemiosmosis
Protons can not
diffuse through the
membrane.
SO they must
flow through the
ATP synthase
protein channel.
90% of all ATP is
produced this way.
“Proton Motive
Force” generates
ATP
Cyclic Photophosphorylation
•Periodically the chloroplasts runs low on ATP.
•Does this to replenish ATP levels.
•e- travel from the P680 ETC to P700 then to
a primary eacceptor,
then back to
the
cytochrome
complex in
the P680
ETC.
Animation
• No NADPH is
produced.
• No O2 is
released.
STAGE 2: Dark Reaction /Light Independent
reaction/Calvin-Benson Cycle).
1. The ATP and NADPH created in the light
reaction are used to power the formation of
Organic Compounds (Sugars), using CO2.
2. This is a light Independent reaction. It can
happen during the daylight, it just does NOT
need light be completed.
3. Occurs in the stroma.
4. Cyclical pathway where carbon enters as CO2
and exits as PGAL (phosphoglyceraldehyde.)
5. Called carbon fixation.
1. Carbon is fixed into PGAL. (2 PGAL=1 Glucose)
6. This is a reduction reaction (carbon is
Review step 1 / Intro to
GAINING hydrogen)
step 2 Clip
7. Must repeat 6 times.
Review of Light Dependent and Intro to Light Independent
C3 plants
The Calvin cycle
6
CO2 attaches to
a 5-C sugarRuBP. Ribulose
biphosphate.
This is called
Fixation
This forms a 6-C
molecule (PGA)
Catalyzes
by the
enzyme
Rubisco.
1)RuBP + CO2  PGA
RuBP
Fixation
PGA
The Calvin cycle
6
PGA is broken down
into 2 3-C molecules
called PGAL
(phosphoglycerate)
RuBP
12
12
12
PGAL
1)RuBP + CO2  PGA
2) PGA+ ATP +NADPH  PGAL
2
PGAL
1
PGA
The Calvin cycle
6
PGAL
converted to
RuBP
RuBP
PGA
12
12
12
PGAL
1)
RuBP + CO2  PGA
Summary:
2
2) PGA+ ATP +NADPH  PGAL
+
6CO
ATP + 12
NADPH
+ H 
2 + 18 Glucose
3) PGAL
+RuBP
regenerated
18ADP + 18 Pi + 12NADP+ + 1 Glucose
PGAL
1
Ted Ed: Calvin Cycle
Problem: RUBISCO catalyzes two different reactions.
Photorespiration
• Occurs when the
CO2 levels inside a
leaf become low.
– Happens on hot dry days
when a plant is forced to
close its stomata to
prevent excess water
loss.
– If the plant continues to
attempt to fix CO2 when
its stomata are closed,
the CO2 will get used up
and the O2 ratio in the
leaf will increase relative
to CO2 concentrations.
•
•
When the CO2
levels inside the
leaf drop to
around 50 ppm,
Rubisco starts
to combine O2
with RuBP
instead of CO2.
The net result
of this is that
instead of
producing 2 3C
PGA molecules,
only one molecule
of PGA is
produced and a
toxic 2C
molecule called
phosphoglycolate
is produced.
Photorespiration
•
•
•
•
The plant must get rid of the phosphoglycolate
Converts it to glycolic acid, which is then transported to the
peroxisome and converted to glycine.
The glycine is then transported into a mitochondria where it is
converted into serine.
The serine is then used to make other organic molecules. All
these conversions cost the plant energy and results in the net
lost of CO2 from the plant.
C3, C4 & CAM Plants
• C-3
– Calvin cycle occurs in all
photosynthetic cells.
– Risk of photorespiration...
• C-4
– C4 plants separate the
site of oxygen production
(PSII) from rubisco
(Calvin cycle).
– Called C-4 because the CO2 is
first incorporated into a 4-carbon
compound.
– Keeps O2 Away from RuBP (NO
Photorespiration)
– Light reaction occurs ONLY in the
mesophyll cells & Calvin cycle
occurs in bundle-sheath cells.
– SPATIAL SEPARTATION
C4 leaf anatomy and the C4 pathway
Different
anatomy
from a C-3
plant
Photosynthesis:
A dry climate
adaptation:
• CAM Plants
(Crassulacean
Acid Metabolism)
-plants live in very dry
condition and, unlike
other plants, open their
stomata to fix CO2 only
at night.
-Fix CO2 at night and
store it.
C4 plants that also have
a TEMPORAL
SEPARTAION
.
Factors affecting Photosynthesis
• Amount of water available – too
little, stop photosynthesis
• Temperature – best between O°C &
35°C (too high, damage enzymes; too
low, stop photosynthesis)
• Intensity of light – up to a point,
increasing light intensity increases rate
of photosynthesis
Spinach Chromatography
•
•
•
•
•
•
•
•
A plant physiology manual (Reiss 1994) identifies six pigments from
spinach leaves extracted with hexane and chromatographed with
petroleum ether-acetone-chloroform (3:1:1) on silica-gl
chromatography. The pigments and their Rf's were:
carotene - 0.98
chlorophyll a - 0.59
chlorophyll b - 0.42
pheophytin - 0.81
xanthophyll 1 - 0.28
xanthophyll 2 - 0.15
The color of the bands can be a general guide to identify the pigments.
Carotene is orange. Chorophylls are green. Chlorophyll a is a blue-green.
Chlorophyll b is a yellow-green. Xanthophylls are yellow. Phaeophytin is
chlorophyll lacking the central magnesium ion. Pheophytin is an olivegreen."
Cellular
Respiration
-The process that occurs in cells in which
cells break down sugar for ENERGY!
Cellular Respiration Overview:
• We get our energy from the food we eat.
• The unit for energy is the calorie.
• Plants are producers and make glucose by
the process of photosynthesis.
• Heterotrophs (consumers) breakdown
glucose for energy.
• There are two important ways a cell can
harvest energy from food: fermentation and
cellular respiration.
Basic overview
1
2
3
• Step 1:
gylcolysis
– Splitting of
glucose into 2
pyruvate
molcules
9 steps
fermentation
cellular
respiration
Glycolysis
Overall Important Points:
• Occurs in Cytoplasm
• Does not require oxygen
Clip;
McGraw
Hill
– Glycolysis occurs in both aerobic (With oxygen) and
anaerobic (without oxygen) respiration.
– Evolved early in Earth’s history (evolutionary relationships)
• First 3 steps are endothermic
– Energy of activation = 2 ATP
• Last 6 steps are exothermic
– producing 4 ATPs.
• 4-2= 2
ATP (net yield)
• Releases less then 25% of energy from glucose.
TYPES of Phosphorlation
• Substrate Level:
– When an enzyme transfers
a PO4- from a substrate
DIRECTLY to ADP.
• Oxidatative:
– During Chemiosmosis.
– 90% of all ATP is produced
this way in the ETC
– NAD & FAD lose protons
(become oxidized) to the
ETC…pumps protons to
innermembrane space
creating a gradient. This
powers the phosphorlation
of ADP
• This is what occurs in the light
reaction in Photosynthesis
A closer look at glycolysis: The 9 Steps
Important
regulatory step;
PFK is inhibited by
ATP
Step 1
Step 2
Step 4
Step 3
PFK
"high
energy"
ecarrying
molecule
A closer look at glycolysis: The 9 Steps
Step 5
Step 6
Substrate-level
phosphorylation
Step 7
Nicotinamide adenine dinucleotide
A closer look at glycolysis: The 9 Steps
Step 5
Step 8
Step 6
Substrate-level
phosphorylation
Step 9
Step 7
3- Carbon Cpd
Net Yield
• 2 NADH
• 2 ATP
Glycolysis Review
What happens next???
In the presence of OXYGEN:
Step 2: Krebs Cycle
Step 3: Electron Transport
• Happens in the
Mitochondria
• Starts with
Pyruvate.
• Pyruvate moves into
the mitochondria
and is broken
completely down into
CO2 , O2 & ATP.
Krebs and ETC take place in a
mitochondrion
Double membrane
Mitochondria Anatomy
Step 2: Krebs Cycle (aka: Citric Acid Cycle)
-Mitochondrial Matrix
Step 3: Electron Transport
-Cristae
Krebs Cycle Overview
Clip;
McGraw
Hill
(Citric Acid Cycle)
• Occurs in the mitochondrial matrix
• Cyclical series of enzyme-catalyzed reactions.
• Pyruvate (product of glycolysis) enters the mito. and
combines with coenzyme A (vitamin A) to form
acetyl coenzyme A.
 Yields 1 NADH
NAD & FAD
Coenzymes that carry protons (H+)
and electrons from glycolysis &
Krebs to the ETC
• Krebs starts with acetyl coA.
• Each turn (cycle) uses 1 pyruvate and yields
• 3 NADH, 1 ATP, 1 FADH
• Byproduct= CO2
How the Krebs Cycle Works
• Occurs in the A summary of the Krebs cycle
mitochondrial matrix
• Pyruvate (product of
glycolysis) enters the
mito. and combines
with coenzyme A
(vitamin A) to form
acetyl coenzyme A.
 Yields 1 NADH
• Krebs starts with
acetyl coA.
• Cyclical series of
enzyme-catalyzed
reactions.
NAD+ &
FAD
-Coenzymes that
carry protons (H+)
and electrons from
glycolysis & Krebs
to the ETC
Krebs Cycle
•Each turn (cycle)
uses 1 pyruvate
Net yield
• 3 NADH,
• 1 ATP,
• 1 FADH
•Byproduct=
CO2
Substrate-level
phosphorylation
The Story So Far…
ETC
Clip;
McGraw
Hill
• 2 NADH
• 2 ATP
• 3 NADH
• 1 ATP
• 1 FADH2
• Byproduct= CO2
ETC Overview
What’s a proton motive force? How is it produced?
Why is it produced –how does it help the cell?
What happens next???
Step 3: Electron Transport
Electron Transport
• The ETC a series of
protiens that serve
to pump protons to
the inner mito
membrane.
• Its uses the energy
released from the
exergonic flow of
electrons.
• This sets up a proton
gradient across the
membrane
=chemiosmosis
“oxidatative
phosphorylation”
The production of ATP using the energy of electrons is called oxidatative
phosphorylation. (where have we seen this before)
Extra Overview Clip
Oxidative Phosphorylation and Chemiosmosis
What happens next???
Energy from falling e- (exergonic) is used
to pump H+ across the membrane
(endergonic).
Clip 2;
Formation
of ATP
Oxygen is the
final eacceptor!!
oxidatative phosphorylation
H+ can’t get through the membrane, so they MUST pass through the channel.
Figure 9.15 Chemiosmosis couples the electron transport chain to ATP synthesis
Oxidative Phosphorylation; The
Phosphorlation of ADP into ATP
by the oxidation of carrier
molecules (NADH & FADH2)
36-38 Total ATP
ETC Review
With & With out
Oxygen
With
oxygen
Glucose
Glycolysis
Krebs
cycle
Fermentation
(without oxygen)
With out
oxygen
Go to
Section:
Electron
transport
Alcohol or
lactic acid
Fermentation
• Without oxygen: Pyruvate is converted
into Lactic Acid or Alcohol during
Fermentation.
40
Anaerobic Respiration
• Lactic Acid- Muscle cells
• Alcohol- Yeast
Fermentation
Lactic Acid Fermentation
Section 9-1
Glucose
Pyruvic acid
Without a means to convert NADH to NAD+,
Glycolysis would shut down
Go to
Section:
Lactic acid
Alternative
Energy Sources
• From Fats:
– Enzymes cleave the bonds
between the glycerol and the
fatty acids, which enter the
blood stream. Enzymes in
the liver convert the glycerol
into PGAL.
– Enzymes in cells break apart
the fatty acids acetyl-CoA.
– More C-H bonds, so yields
more ATP.
Alternative
Energy Sources
• From Proteins:
– Cells don’t store protein.
– Enzymes breakdown
proteins—into AA units,
then strip of the NH3+
group.
– Carbon backbone either
gets converted into fats or
carbohydrates.
– Or, enter krebs cycle.
Calvin Cycle (extra video)