Chapter 10~Photosynthesis

1
Chapter 10 Photosynthesis
2
(No Transcript)
3
The chloroplast
4
Photosynthesis

• Light reactions
• light-dependent reactions
• energy conversion reactions
• convert solar energy to chemical energy
• ATP NADPH
• Calvin cycle
• light-independent reactions
• sugar building reactions
• uses chemical energy (ATP NADPH) to reduce CO2
  synthesize C6H12O6

Its not theDark Reactions!
5
Light reactions
thylakoid
chloroplast
ATP

• Electron Transport Chain
• like in cellular respiration
• proteins in organelle membrane
• electron acceptors
• NADPH
• proton (H) gradient across inner membrane
• find the double membrane!
• ATP synthase enzyme

6

• Chloroplasts transform light energy into chemical
  energy of ATP
• use electron carrier NADPH

ETC of Photosynthesis
generates O2
7
Pigments of photosynthesis
How does thismolecular structurefit its
function?

• Chlorophylls other pigments
• embedded in thylakoid membrane
• arranged in a photosystem
• collection of molecules
• structure-function relationship

8
Photosynthetic Pigments

• Pigment - substance that absorbs light
• Absorption spectrum - measures the wavelength of
  light that absorbed by particular pigment
• Accessory pigments - absorbs energy that
  chlorophyll a does not absorb ensures that a
  greater of incoming photons will stimulate
  photosynthesis
• Action spectrum - plots the efficiency of
  photosynthesis at various wavelengths

9
Photosystems

• Light harvesting units of the thylakoid membrane
• Composed mainly of protein and pigment antenna
  complexes
• Antenna pigment molecules are struck by photons
• Energy is passed to reaction centers (redox
  location)
• Excited e- from chlorophyll is trapped by a
  primary e- acceptor

10
Photosystems of photosynthesis

• 2 photosystems in thylakoid membrane
• collections of chlorophyll molecules
• Photosystem II
• chlorophyll a
• P680 absorbs 680nm wavelength red light
• Photosystem I
• chlorophyll b
• P700 absorbs 700nm wavelength red light

reactioncenter
antennapigments
11
ETC of Photosynthesis
chlorophyll a
chlorophyll b
12
ETC of Photosynthesis
sun
1
Photosystem IIP680chlorophyll a
13
ETC of Photosynthesis
Inhale, baby!
thylakoid
chloroplast
ATP
Plants SPLIT water!
1
2
O
O
e
e
fill the e vacancy
Photosystem IIP680 chlorophyll a
14
ETC of Photosynthesis
thylakoid
chloroplast
ATP
3
1
2
ATP
4
energy to buildcarbohydrates
Photosystem IIP680 chlorophyll a
ATP
15
ETC of Photosynthesis
sun
fill the e vacancy
5
e
e
Photosystem IP700 chlorophyll b
Photosystem IIP680 chlorophyll a
16
ETC of Photosynthesis
electron carrier
6
5
sun
Photosystem IP700 chlorophyll b
Photosystem IIP680 chlorophyll a
in the bankreducing power!
17
ETC of Photosynthesis
sun
sun
O
to Calvin Cycle
split H2O
ATP
18
ETC of Photosynthesis

• ETC uses light energy to produce
• ATP NADPH
• go to Calvin cycle
• PS II absorbs light
• excited electron passes from chlorophyll to
  primary electron acceptor
• need to replace electron in chlorophyll
• enzyme extracts electrons from H2O supplies
  them to chlorophyll
• splits H2O
• O combines with another O to form O2
• O2 released to atmosphere
• and we breathe easier!

19
Noncyclic Photophosphorylation

• Light reactions elevate electrons in 2 steps (PS
  II PS I)
• PS II generates energy as ATP
• PS I generates reducing power as NADPH

ATP
20
Photophosphorylation
cyclic photophosphorylation
NONcyclic photophosphorylation
ATP
21
Photosynthesis The Calvin Cycle
22
The Calvin Cycle
1950s 1961
Whoops! Wrong Calvin
23
Light reactions

• Convert solar energy to chemical energy
• ATP
• NADPH
• What can we do now?

ATP
? energy
? reducing power
? ? build stuff !!
photosynthesis
24
How is that helpful?

• Want to make C6H12O6
• synthesis
• How? From what? What raw materials are available?

CO2
NADPH
reduces CO2
carbon fixation
NADP
25
From CO2 ? C6H12O6

• CO2 has very little chemical energy
• fully oxidized
• C6H12O6 contains a lot of chemical energy
• highly reduced
• Synthesis endergonic process
• put in a lot of energy
• Reduction of CO2 ? C6H12O6 proceeds in many small
  uphill steps
• each catalyzed by a specific enzyme
• using energy stored in ATP NADPH

26
From Light reactions to Calvin cycle
27
C
C
Calvin cycle
C
1. Carbon fixation
3. Regenerationof RuBP
RuBP
RuBisCo
ribulose bisphosphate
starch,sucrose,cellulose more
ribulose bisphosphate carboxylase
used to makeglucose
glyceraldehyde-3-P
PGA
G3P
phosphoglycerate
2. Reduction
28
To G3P and Beyond!
To G3Pand beyond!

• Glyceraldehyde-3-P
• end product of Calvin cycle
• energy rich 3 carbon sugar
• C3 photosynthesis
• G3P is an important intermediate
• G3P ? ? glucose ? ? carbohydrates
• ? ? lipids ? ? phospholipids, fats, waxes
• ? ? amino acids ? ? proteins
• ? ? nucleic acids ? ? DNA, RNA

29
RuBisCo

• Enzyme which fixes carbon from air
• ribulose bisphosphate carboxylase
• the most important enzyme in the world!
• it makes life out of air!
• definitely the most abundant enzyme

Im green with envy!
Its not easy being green!
30
Light Reactions
H2O

• produces ATP
• produces NADPH
• releases O2 as a waste product

Energy Building Reactions
NADPH
ATP
O2
31
Calvin Cycle

• builds sugars
• uses ATP NADPH
• recycles ADP NADP
• back to make more ATP NADPH

CO2
ADP
NADP
SugarBuilding Reactions
NADPH
ATP
sugars
32
Putting it all together

• Plants make both
• energy
• ATP NADPH
• sugars

H2O
CO2
ADP
NADP
SugarBuilding Reactions
Energy Building Reactions
NADPH
ATP
sugars
O2
33
Supporting a biosphere

• On global scale, photosynthesis is the most
  important process for the continuation of life
  on Earth
• each year photosynthesis
• captures 121 billion tons of CO2
• synthesizes 160 billion tons of carbohydrate
• heterotrophs are dependent on plants as food
  source for fuel raw materials

34
Controlling water loss from leaves

• Hot or dry days
• stomates close to conserve water
• guard cells
• gain H2O stomates open
• lose H2O stomates close
• adaptation to living on land, but
• creates PROBLEMS!

35
When stomates close

• Closed stomates lead to
• O2 build up ? from light reactions
• CO2 is depleted ? in Calvin cycle
• causes problems in Calvin Cycle

The best laidschemes ofmice and menand
plants!
xylem (water)
phloem (sugars)
?
?
36
Calvin cycle when CO2 is abundant
RuBisCo
G3P to make glucose
C3 plants
37
to mitochondria lost as CO2 without
making ATP
Calvin cycle when O2 is high
Hey Dude, are you highon oxygen!
RuBisCo
Its so sad to see agood enzyme,go BAD!
photorespiration
38
Impact of Photorespiration

• Oxidation of RuBP
• short circuit of Calvin cycle
• loss of carbons to CO2
• can lose 50 of carbons fixed by Calvin cycle
• reduces production of photosynthesis
• no ATP (energy) produced
• no C6H12O6 (food) produced
• if photorespiration could be reduced, plant would
  become 50 more efficient
• strong selection pressure to evolve alternative
  carbon fixation systems

39
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

40
C4 vs CAM Summary
solves CO2 / O2 gas exchange vs. H2O loss
challenge
CAM plants separate 2 steps of C fixation
temporally 2 different times night vs. day
C4 plants separate 2 steps of C fixation
anatomically in 2 different cells