PHOTOSYNTHESIS Bio 11 Mr. McIntyre

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PHOTOSYNTHESISBio 11 Mr. McIntyre
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Simple Photosynthesis Overview

• Simplified Chemical summary
• 6CO2 6H2O energy (sun) ? C6H12O6 6O2

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Properties of Light

• http//www.phschool.com/science/biology_place/bioc
  oach/photosynth/electro.html

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Structure of a Leaf

• Label the diagram provided by Mr. A.
• Take this test...

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Stoma

• This structure allows for the plant to exchange
  gasses with its environment. What gasses??

• Stoma
• Guard cells

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Chloroplast structure

• http//Animation Show first 20 sec for
  chloroplast anatomy

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Photosynthesis An Overview of the Light and
Dark Reactions

• Occurs in Photoautotrophs (organisms that can
  make their own using energy from the sun).
• Photosynthesis takes place in the chloroplasts.
• Photosynthesis includes two processes

http//simple animation

• LIGHT REACTIONS
• (aka photophosphorylation)
• Requires sunlight
• Occurs in the granna of chloroplasts
• Produces ATP and NADPH (used to power the Calvin
  cycle)

• DARK REACTIONS (a misnomer) (aka Calvin cycle)
• Doesnt require sunlight (happens 24/7).
• Occurs in the stroma of chloroplasts
• Produces glucose

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Micrograph of Chloroplast
take a quiz!

• http//indycc1.agri.huji.ac.il/zacha/chloroplast.
  jpg

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Photosystems

• Photosystems are arrangements of chlorophyll and
  other accessory pigments packed into thylakoids.
• Many prokaryotes have only one photosystem,
  Photosystem I. Eukaryotes have Photosystem I plus
  Photosystem II.

• Photosystem I uses chlorophyll a, in the form
  referred to as P700. It absorbs light at 700 nm.
  Photosystem II uses a form of chlorophyll a known
  as P680. It absorbs light at 680 nm.
• The accessory pigments (chlorophyll b, carotenes,
  and xanthophylls) play an indirect role in the
  formation of glucose through photosynthesis.
  These pigments provide chlorophyll a with the
  energy that they have captured from the sun.
  These pigments capture varying wavelengths of
  light and thus allow the plant to receive sun
  energy across a greater spectrum Accessory
  pigments absorb energy that chlorophyll a does
  not absorb.

Graphic http//kvhs.nbed.nb.ca/gallant/biology/ph
otosystem.jpg
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Phosphorylation

• Phosphorylation The chemical addition of a
  phosphate group (phosphorous and oxygen) to a
  compound. i.e. adding Pi to ADP to get ATP
• Photophosphorylation is addition of a phosphate
  using the suns energy!
• There are two types of photophosphorylation
  cyclic and non-cyclic

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Cyclic Photophosphorylation (In bacterial
photosynthesis)

• A single photosystem is involved.
• A photon of light strikes a pigment molecule in
  the P700 antenna system.
• The energy eventually reaches a molecule of P700
  (specialized chlorophyll A - the reaction
  centre). This electron is ejected from the
  photosystem.
• The energized electron leaves P700 and is passed
  to an acceptor molecule Ferrodoxin (fd).
• The electron is then passed through the
  cytochrome b6f complex. This complex pumps
  protons (H) into the space between bacteriums
  cell membrane and capsule. This creates a proton
  gradient.
• Protons can only exit the thylakoid space via ATP
  synthase. ATP synthase uses the energy flow of
  protons (proton motive force) to make ATP
  (Phosphorylaion).

Animation 1 Development of Proton Motive Force
(proton gradient)
Animation 3 ATP synthase
Animation 2 Formation of ATP from Proton motive
force
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Cyclic Photophosphorylation

• The electron is then passed through the
  plastocyanin (pC).
• The electron is passed back to the reaction
  centre.
• The electrons energy is gradually lost during
  this process.
• The de-energized electron returns to the
  chlorophyll A molecule to be energized again.
• We call this process cyclic photophosphorylation
  because electrons return to the photosystem and
  are then again energized. The process is a cycle!
• The energy released during this electron
  transport generates a proton gradient which is
  used to produce ATP.
• Animation (non) cyclic photophosphorylation
  animation

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NON-cyclic photo-phosphorylation
Hmmmm
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Non-Cyclic Photophosphorylation

• Happens in PLANTS. Two photosystems are involved.
• A photon hits Photosystem II (PS II or P680).
  This energy is relayed to the reaction centre via
  accessory pigments. A high energy electron is
  emitted.
• meanwhile, an enzyme in PS II splits water. The
  oxygen is released as a byproduct. Electrons from
  water are used to replace those lost by PS II.
• The electron excited in PS II then travels to
  plastoquinone (Q), then to the b6f complex
  (proton pump).

• The proton pump uses this energy to pump protons
  across the thylakoid membrane, from the stroma
  into the thylakoid space. These protons can only
  exit the thylakoid via ATP synthase. The flow of
  protons through ATP synthase is used to make ATP.

Proton pump
Fd
PC
Q
NADP Reductase
Animation (non) cyclic photophosphorylation
animation
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..Non-Cyclic Photophosphorylation

• The electron then goes to plastocyanin (PC) and
  then to PS I.
• Remember, the electron has lost energy
  becausethe proton pump used it up! Its now
  de-energized!
• A photon hits PS I (P 700). Energy is passed
  from accessory pigments to reaction centre which
  ejects a high energy electron.

• The de-energized electron replaces the electron
  lost from PS I.

Proton pump
Fd
PC
Q
NADP Reductase
Animation (non) cyclic photophosphorylation
animation
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Non-Cyclic Photophosphorylation

• The electron is then passes to ferrodoxin (Fd)
  and then to NADP reductase, which uses the newly
  energized electron to reduce NADP to NADPH.
• The ATP and NADPH produced during non-cyclic
  photophosphorylation go to the Calvin cycle to
  provide energy and raw materials to make SUGAR!

Proton pump
Fd
PC
Q
NADP Reductase
Animation (non) cyclic photophosphorylation
animation
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NON-cyclic photo-phosphorylation Does this make
sense now?
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Watch the animation, then answer this
questionWhere do the protons come from that go
through ATP synthase?
animation non-cyclic photophosphorylation
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Examine the formula that summarizes
photosynthesis
sunlight

• CO2 H2O C6H12O6 O2

• You should know
• Where the O2 byproduct comes from
• Infer
• Where the carbon in glucose comes from
• Where the hydrogen in glucose comes from
• Where the oxygen in glucose comes from

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The Calvin Cycle

• In Photosynthesis, ATP and NADPH are produced in
  photophosphorylation, aka the Light Reactions.
  This happens in the thylakoid. The next series
  of reactions, the Calvin cycle, happens in the
  stroma. This is where sugars are manufactured.
  Melvin Calvin discovered this cycle in 1940.

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The Calvin Cycle

• The end product of photosysnthesis isnt really
  glucose its PGAL (phosphoglyceraldehyde). PGAL
  can be used to manufacture glucose, or other
  sugars, fatty acids or amino acids.
• The Calvin Cycle has three phases
• 1st phase Carbon Fixation
• 2nd phase Reduction
• 3rd phase Regeneration of the Carbon acceptor
  molecule (RuBP)

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1st Phase Carbon Fixation 1. Three five-carbon
sugar molecules called ribulose bisphosphate, or
RuBP, are the acceptors that bind 3 CO2
molecules (dissolved in the stroma). This
reaction is catalyzed by the enzyme rubisco. 2.
Three unstable 6-C molecules are produced (not
shown) which quickly break down to give six
molecules of the three-carbon phosphoglyceric
acid (PGA).
The Calvin Cycle
3 x CO2
1
2
6 x PGA 3-C
3 x RuBP (5-C)
Rubisco
Animation Calvin cycle
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• 2nd Phase Reduction
• 3. The six PGA molecules are converted into six
  phosphoglyceraldehyde (PGAL) molecules, a
  three-carbon sugar phosphate, by adding
  high-energy phosphates group from ATP molecules,
  then breaking the phosphate bond and adding
  hydrogen from NADPH.
• 4. Six molecules of PGAL are produced. However,
  only one of the six molecules exits the cycle as
  an output (to make sugar, etc.) while...

The Calvin Cycle
3 x CO2
1
2
6 x PGA (3-C)
3 x RuBP (5-C)
Rubisco
6 x ATP
3
6 x ADP
6 x NADPH
6 x NADP
6 x Pi
6 x PGAL (3-C)
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Animation Calvin cycle
PGAL
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• 3rd Phase Regeneration of the Carbon acceptor
  molecule (RuBP)
• 5. ...the remaining five enter a complex process
  that regenerates more RuBP to continue the
  cycle....
• 6. In this process, ATP is used to convert the
  five PGALs to three RuBPs.
• 7. Summary...
• 9 ATP used
• 6 NADPH used
• 1 PGAL produced
• RuBP regenerated

The Calvin Cycle
3 x CO2
1
2
6 x PGA (3-C)
3 x RuBP (5-C)
Rubisco
6 x ATP
3
6 x ADP
3 x ADP
3 x ATP
6 x NADPH
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6 x NADP
6 x Pi
6 x PGAL (3-C)
5 x PGAL (3 C)
5
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Animation Calvin cycle
1 x PGAL (3-C)
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Overview of light dependent reactions