2. Electron carriers
Electrons in chlorophyll
Sun excites them
Electrons gain E
These high E electrons require special
carrier
High E e- are similar to hot coals that need
to be transferred
Electron carriers needed to transport high-
E e-
NADP+
Nicotinamide adenine dinucleotide
phosphate (Just remember NADP)
Accepts 2 high-E e- to become
NADPH
This is how energy (e-) from sun can
be trapped in chemical form
NADPH carries high-E e- from
chlorophyll to other parts of the
chloroplast
Help build molecules, such as glucose
3.
4. Photosystems
Clusters of chlorophyll and other pigments in the
thylakoid membrane (organized by a set of proteins in
the plant cell)
Contain few hundred pigment molecules
Chlorophyll a (absorbs 680 nm wavelengths)
Chlorophyll b (absorbs 700 nm wavelengths)
Carotene/carotenoids
Light-collecting unit of the cell
Solar panel
Photosystem II (P680) and
Photosystem I (P700)
5.
6.
7. Light Dependent
Reactions
Produce oxygen gas and convert ADP and NADP+ into the
energy carriers ATP and NADPH
Take place in the THYLAKOID membrane of chloroplast
Begins with photosystem II
(this was discovered after photosystem I but actually occurs before it)
Photosystem II traps light E and transfers excited e- to an ETC
“water-splitting” photosystem
Light absorbed by photosystem II is used to break-up water molecules
into high-E electrons, oxygen, and H+ ions
2 electronsreplace lost e- in chlorophyll
2 H+ ions released into the inside of the thylakoid membrane
1 oxygen atom oxygen released into atmosphere
Electrons in chlorophyll are excitedpassed along ETCdo
electrons in chlorophyll run out?
No: the high-E electrons lost by the chlorophyll are replaced by the
electrons from “water splitting”
8. High-E electrons move through the ETC from
photosystem II to photosystem I
Energy from electrons is used by molecules in
the ETC to transport H+ ions from the stroma
into the inner thylakoid space
9. Pigments in photosystem I use Energy from
light to re-energize the electrons
NADP+ then picks up these high-E electrons
and H+ ions at the outer surface of the
thylakoid membrane
NADP+ becomes NADPH
10. As electrons are passed from chlorophyll to
NADP+, H+ ions are pumped across
membrane
Inside of thylakoid membrane fills up with
positive H+ ions, outside in negative
Chemosmosis occurs
ATP synthase turns making ADPATP
11. ETC proteins
Photosystem II (recieves light & splits water)
Oxygen-evolving complex
Plastoquinone
Cytochrome
Plastocyanin
Photosystem I (receives more light)
Ferredoxin
Ferrdoxin-NADP reductase
NADPNADPH
ATP synthase
ADPATP
12.
13.
14.
15.
16.
17. Overview of Light
Dependent Rxn
Use:
ADP
NADP+
Water
Produce:
Oxygen
ATP
NADPH
Why are these products important?
Provide energy to build energy-containing sugars
from low-energy compounds in Calvin cycle
18. Calvin Cycle/ Light-
Independent Reactions
So what do we have from pour light-dependent
rxns?
High-E electrons stored in ATP and NADPH
“chemical energy”
But plants cannot store this chemical energy for
more than a few minutes…must change this
chemical energy into something that can be stored
for long periods of time
Calvin cycle
Uses ATP and NADPH from light-dependent rxn to
produce high-E sugars
19.
20.
21.
22. Important concept!
ONE carbon dioxide enters the Calvin
cycle at a time
Calvin cycle must turn THREE times to
make the first small, three-carbon sugar
Calvin cycle must turn SIX times to have
two small, three carbon sugars to throw
together to make GLUCOSE
23. Step 1
THREE TURNS:
Three carbon dioxide molecules enter cycle from atmosphere
Enzyme adds each CO2 molecule to a Ribulose biphosphate,
RuBP molecule (a 5-carbon molecule) making three unstable 6-
carbon molecules
The 3 unstable 6-carbon molecules immediately break off into six 3-
carbon molecules called 3-phosphoglycerate, 3-PGA
Add six ATPs to make each of the 3PGAs into DPGA
3-PGAs + ATP1, 3-biphosphoglycerate
24.
25. Step 2
THREE TURNS:
Six 3-carbon molecules are converted into
higher energy forms using energy from ATP
and high-E electrons from NADPH
Six 3-PGAs are converted into Six
energized Glyceraldehyde 3-phosphates
(G3P).
1, 3-biphosphoglycerate + NADPH
Glyceraldehyde 3-phosphate
26.
27. Step 3
One of the G3Ps (we had a total of 6 of
these 3-carbon molecules) is removed
from the cycle
This G3P waits for the Calvin cycle to
turn again and release another one to
make GLUCOSE (or other
sugars, lipids, amino acids, and other
compounds plant needs for metabolism
and growth)
28.
29. Step 4
Remaining five G3Ps (3-carbon
molecules) use ATP and rearrange
themselves
ADP and NADP+ go back to light rxns
Converted back into RuBP molecules
(three 5-carbon molecules)
Calvin cycle begins again with the next
three CO2 molecules
30.
31. Calvin cycle overview
Three turns… Six turns…
Uses: Uses:
Three molecules of Six molecules of CO2
CO2 NADPH
NADPH ATP
ATP Produces:
Produces: Two G3P’s (PGALs)
One 3-carbon sugar that we put together to
called G3P or make …One 6-carbon
PGAL sugar “glucose”
32.
33.
34.
35. Photosynthesis overview
Two sets of reactions work together
Light dependent
Trap energy of sunlight into chemical form
Calvin cycle/light independent
Use chemical energy to produce stable-high
energy sugars from carbon dioxide and water
36. Factors that effect rate of
photosyntehsis
Water availability
Shortage of water can slow or stop photosyn.
Adaptations
Desert plants and conifers
Waxy coating
Temperature
Photosyn. Depends on enzymes that function between 0*C
and 35*C
Low temp. may cause photosyn. to stop
Intensity of light
Increase light intensity=increase rate of photosynthesis
After a certain level of intensity, plant reaches its max rate of
photosynthesis
37.
38. Problems
Calvin cycle- RuBP binds with CO2 to make 6-C compound
that changes immediately into 3- Carbon compounds that
eventually make G3P then sugar
Enzyme that catalyzes this reaction is called Rubisco
Problem with Rubisco is that its not good at grabbing
CO2…gets easily confused by oxygen
When levels of CO2 inside cell are low, Rubisco starts
grabbing oxygen
This cause photorespiration
When plant uses light and consumes oxygen, producing
carbon dioxide
This uses up energy…NOT good
Big problem on hot, dry days when stomata close and
can’t get CO2
So how do plants deal?
39.
40. Reducing photorespiration
Separate carbon fixation from Calvin cycle
C4 plants
PHYSICALLY separate carbon fixation from Calvin cycle
different cells to fix carbon vs. where Calvin cycle occurs
store carbon in 4C compounds
different enzyme to capture CO2 (fix carbon)
PEP carboxylase
different leaf structure
CAM plants
separate carbon fixation from Calvin cycle by TIME OF DAY
fix carbon during night
store carbon in 4C compounds
perform Calvin cycle during day
41. Comparative anatomy
Location,
location,location!
C3 C4
PHYSICALLY separate C fixation from Calvin cycle
42. C4 plants
A better way to capture CO2
1st step before Calvin cycle,
fix carbon with enzyme
PEP carboxylase
store as 4C compound corn
adaptation to hot,
dry climates
have to close stomates a lot
different leaf anatomy
sugar cane, corn,
other grasses…
43. Comparative anatomy
Location,
location,location!
C3 C4
PHYSICALLY separate C fixation from Calvin cycle
44. Special Plants
C4 plants
"four-carbon”
plants initially attach CO 2 to PEP
(phosphoenolpyruvate) to form the four-
carbon compound oxaloacetate using
the enzyme PEP carboxylase.
This takes place in mesophyll cells.
Oxaloacetate is then pumped to another
set of cells, the bundle sheath cells,
In the bundle sheath cells it releases the
CO 2 for use by Rubisco.
Now plant can use Calvin Cycle
By concentrating CO 2 in the bundle
sheath cells, C4 plants promote the
efficient operation of the Calvin cycle
and minimize photorespiration.
C4 plants include corn, sugar cane, and
many other tropical grasses
45. CAM (Crassulacean Acid
Metabolism) plants
Adaptation to hot, dry climates
separate carbon fixation from Calvin cycle by TIME
close stomates during day
open stomates during night
at night: open stomates & fix carbon
in 4C “storage” compounds
in day: release CO2 from 4C acids
to Calvin cycle
increases concentration of CO2 in cells
succulents, some cacti, pineapple
46. Special Plants
CAM (crassulacean acid metabolism) plants
plants initially attach CO 2 to PEP (phosphoenolpyruvate) to form the four-
carbon compound oxaloacetate using the enzyme PEP carboxylase.
CAM plants fix carbon at night and store the oxaloacetete (organic acid)
in large vacuoles within the cell.
During the day, CO2 is released from these organic acids and used in the
Calvin cycle
Then they can open their stomatas at night (cool weather) and lets CO2
The avoid water loss and to use the CO 2 for the Calvin cycle during the
day when it can be driven by the sun's energy.
CAM plants are more common than C4 plants
Ex. Are cacti, pineapples and other succulent plants.
48. C4 vs CAM Summary
solves CO2 / O2 gas exchange vs. H2O loss challenge
C4 plants CAM plants
separate 2 steps separate 2 steps
of C fixation of C fixation
anatomically in 2 temporally =
different cells 2 different times
night vs. day