The production of ATP AND NADPH the light reaction of photosynthesis

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• The production of ATP AND NADPH the light
  reaction of photosynthesis

Thylakoidcompartment(high H)
Light
Light
Thylakoidmembrane
Antennamolecules
Stroma(low H)
ELECTRON TRANSPORT CHAIN
PHOTOSYSTEM II
PHOTOSYSTEM I
ATP SYNTHASE
Figure 7.9
2
ATP and NADPH power sugar synthesis in the Calvin
cycle

• The Calvin cycle occurs in the chloroplasts
  stroma
• This is where carbon fixation takes place and
  sugar is manufactured

INPUT
CALVINCYCLE
Figure 7.10A
OUTPUT
3

• Details of the Calvin cycle

INPUT
3
In a reaction catalyzed by rubisco, 3 molecules
of CO2 are fixed.
CO2
Step Carbon fixation.
1
1
3
P
P
P
6
RuBP
3-PGA
6
ATP
3 ADP
Step Energy consumption
2
6 ADP
P
CALVINCYCLE
3
ATP
2
6
NADPH
4
6 NADP
Step Release of one molecule of G3P.
3
6
P
5
P
G3P
G3P
3
Step Regeneration of RuBP.
4
Glucoseand other compounds
OUTPUT
1
P
G3P
Figure 7.10B
4
Step 1carbon Fixation

• CO2 is incorporated (fixed) into a five-carbon
  sugar named ribulose bisphosphate (RuBP).
• The enzyme that does this is RuBP carboxylase or
  rubisco.
• The most abundant protein protein on Earth.
• The product is a six-carbon intermediate which
  immediately splits in half to form two molecules
  of 3-phosphoglycerate (3PGA).

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Step 2Energy consumption

• ATP and NADPH2 (from the light reaction) are used
  to convert 3-phosphoglycerate (3GPA) to
  glyceraldehyde 3-phosphate (G3P)
• three-carbon carbohydrate precursor to glucose
  and other sugars.

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Step 3Output of G3P

• output is one molecule of glyceraldehyde
  3-phosphate
• For every three molecules of CO2 that enter the
  cycle, the net output is one molecule of
  glyceraldehyde 3-phosphate
• Used to make Glucose

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Step 4Regeneration of RuBP

• ATP is used to regenerate RuBP from G3P

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Energy cost of Calvin Cycle

• For each G3P synthesized, the cycle spends
• 9 ATP
• 6 NADPH2.
• Both are made in the light reaction

9

• http//highered.mcgraw-hill.com/sites/0070960526/s
  tudent_view0/chapter5/animation_quiz_1.html

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Review Photosynthesis uses light energy to make
food molecules

• A summary of the chemical processes of
  photo-synthesis

Chloroplast
Light
Photosystem IIElectron transport chains
Photosystem I
CALVIN CYCLE
Stroma
Electrons
Cellular respiration
Cellulose
Starch
Other organic compounds
LIGHT REACTIONS
CALVIN CYCLE
Figure 7.11
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• Many plants make more sugar than they need

• The excess is stored in roots, tubers, and fruits
• These are a major source of food for heterotrophs

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C4 and CAM plants have special adaptations that
save water

• Most plants are C3 plants, which take CO2
  directly from the air and use it in the Calvin
  cycle
• In these types of plants, stomata on the leaf
  surface close when the weather is hot
• This causes a drop in CO2 and an increase in O2
  in the leaf
• Photorespiration may then occur
• No sugar or ATP

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• Photorespiration in a C3 plant

CALVIN CYCLE
2-C compound
Figure 7.12A
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• Some plants have special adaptations that enable
  them to save water

• Special cells in C4 plantscorn and
  sugarcaneincorporate CO2 into a four-carbon
  molecule
• This molecule can then donate CO2 to the Calvin
  cycle

4-C compound
CALVIN CYCLE
3-C sugar
Figure 7.12B
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• The CAM plantspineapples, most cacti, and
  succulentsemploy a different mechanism

• They open their stomata at night and make a
  four-carbon compound
• It is used as a CO2 source by the same cell
  during the day

4-C compound
Night
Day
CALVIN CYCLE
3-C sugar
Figure 7.12C
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PHOTOSYNTHESIS, SOLAR RADIATION, AND EARTHS
ATMOSPHERE

• Due to the increased burning of fossil fuels,
  atmospheric CO2 is increasing
• CO2 warms Earths surface by trapping heat in the
  atmosphere
• This is called the greenhouse effect

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Sunlight
ATMOSPHERE
Radiant heat trapped by CO2 and other gases
Figure 7.13A B
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• Because photosynthesis removes CO2 from the
  atmosphere, it moderates the greenhouse effect

• Unfortunately, deforestation may cause a decline
  in global photosynthesis

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• Mario Molino received a Nobel Prize in 1995 for
  his work on the ozone layer
• His research focuses on how certain pollutants
  (greenhouse gases) damage that layer

Figure 7.14A
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Sunlight
ATMOSPHERE
Radiant heat trapped by CO2 and other gases
Figure 7.13A B
21

• Because photosynthesis removes CO2 from the
  atmosphere, it moderates the greenhouse effect

• Unfortunately, deforestation may cause a decline
  in global photosynthesis

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7.14 Talking About Science Mario Molina talks
about Earths protective ozone layer

• Mario Molino received a Nobel Prize in 1995 for
  his work on the ozone layer
• His research focuses on how certain pollutants
  (greenhouse gases) damage that layer

Figure 7.14A
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• The O2 in the atmosphere results from
  photosynthesis

• Solar radiation converts O2 high in the
  atmosphere to ozone (O3)
• Ozone shields organisms on the Earths surface
  from the damaging effects of UV radiation

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• Industrial chemicals called CFCs have hastened
  ozone breakdown, causing dangerous thinning of
  the ozone layer

Sunlight

• International restrictions on these chemicals are
  allowing recovery

Southern tip of South America
Antarctica
Figure 7.14B