Photosynthesis: The Transformation of Matter and Energy

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Photosynthesis The Transformation of Matter
and Energy

• Matter is transformed from inorganic materials
  (CO2 and H from H2O) into organic molecules
  sugar.
• Energy is transformed from light into chemical
  energy (the light energy is absorbed by the
  electrons of H and the energy is stored in the
  bonds of the sugar)
• Cellular Respiration
• Breaking apart the sugar and releasing the energy
  stored in the bonds

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Leaf Structure
Palisades capture light energy Spongy
captures light energy and allows for circ. of
gases Epidermis protects leaf from dehydration
and disease Cuticle produced by epidermis
made of lipid Vein brings water to leaves and
transports sugar away from leaves Stomates
lets in CO2 lets out O2 and H2O Guard Cells
opens and closes stomates
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Structure/Function Relationships in the Leaf

• Palisades main photosynthetic cells lined up
  so more fit/at top for better light absorption
• Epidermis protect leaf from disease and
  dehyration because it is on the very outside of
  the leaf and is rectangular so they fit together
  tightly and do not allow anything to pass between
  the cells. They secrete the cuticle which is
  made of lipids and is non-polar and therefore
  seals the cells so that no water which is polar
  can go through
• Stomates holes that let CO2 in and O2 out
  some on top, most on bottom, controlled by guard
  cells. This allows them to let the gas exchange
  happen without losing too much water vapor. When
  really hot and dry, guard cells can close them
  and at night when cant photsynthesize anyway
  without the light. Also, by being on bottom
  which is cooler lose less water

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Structure/Function Cont.

• Spongy away from sun but still maximize overall
  light absorption by providing more chloroplasts/
  at bottom near stomates where most of CO2 enters
  so it can more easily circulate and get to all of
  the cells that are photosynthetic since dont
  want too many stomates on top
• Veins- in the middle to supply water to and pick
  up food from the photosynthetic cells. Made of
  many cells instead of being hollow to maximize
  adhesion to move the water from roots to leaves
  without supplying energy

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Chloroplast Structure
Thylakoid Flattened sacs made of membranes
Contains chlorophyll, proton pumps and electron
carriers Site of light reactions
Grana Stack of Thylakoids
Stroma liquid part around thylakoids Contains
enzymes for Calvin Cycle Contains DNA, RNA, and
ribsomes so chloroplast can make few of its own
proteins
Chlorophyll Colored pigment that absorbs the
suns energy Absorbs red and blue visible light
and reflects mainly green
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Electromagnetic Spectrum
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Absorance spectrum of chlorophyll vs. Action
Spectrum
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Why the Absorbance and Action Spectra Different?
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Redox Reactions

• Oil rig oxidation is losing, reduction is
  gaining
• Since one atom or molecule cant lose an electron
  without something else accepting it,
  oxidation/reduction reactions MUST happen in
  pairs (one thing gets oxidized, the other gets
  reduced i.e. takes the electrons from the other
  thing)
• Photosynthesis is a series of oxidation/reduction
  reactions!

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Overall Reactions of Photosynthesis
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Light Reactions

• Photosystem complex of pigments (chlorophyll
  and accessory pigments) and proteins that
  organize the pigments
• Reaction Center chlorophyll molecule in the
  photosystem that contains the primary electron
  acceptor so this is the place where electrons
  are actually removed from the chlorophyll

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The structure of chlorophyll the antenna pigment
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Photosystem
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The two photosytems of photosynthesis
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Flow of Electrons Thru the Photosystems
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Light Reactions
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Steps of the Light Reactions

• Electrons of hydrogens on chlorophyll in
  Photosystem 2 (p680) are excited by visible light
  rays (blue and red) and move to the reaction
  center
• These electrons leave the reaction center on the
  primary electron acceptor
• Simultaneously, light energy splits water and
  with the help of enzymes the H and electrons from
  water are put on chlorophyll to replace the ones
  that are leaving oxygen is given off as a
  bi-product and goes off into the atmosphere

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Light Reactions continued

• The first carrier of the electron transport chain
  grabs the electrons from the primary electron
  acceptor
• As the electrons are passed down each successive
  carrier, energy is given off resulting in ATP
  formation by chemiosmosis
• The electrons end up at photosystem I (p700)
• All electrons in PI are passed to the reaction
  center and leave via the primary electron acceptor

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Light Reactions still cont.

• The p.e.a. passes it to Fd and then an enzyme
  passes it to NADP which becomes NADPH
• NADPH carries the electrons and H to the stroma
  for the Calvin cycle
• More ATP can be made in cyclic photophosphorylatio
  n when Fd passes the electrons back through the
  e.t.c which again end up at PI to be excited again

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Chemiosmosis coupling of energy lost by
electrons to the making of ATP

• As e- are passed down the etc, energy is lost
• That energy is used to pump H into the thylakoid
  (1000x difference in conc.)
• The H flow back to the stroma through specially
  shaped protein channels which contain the enzyme
  ATPsynthase.
• The flow of H causes a shape change in the
  enzyme that allow it to catalyze adding P to ADP
  to make ATP
• Using the suns energy to generate ATP thru
  chemiosmosis is called photophosphorylation

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ATP Synthase
ATP Synthase Video
New ATP Synthase Video
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Cyclic vs. Non Cyclic Photophosphorylation

• Non cyclic is the ATP generated from the
  electrons going straight through the path from
  water to NADPH.
• Cyclic is the ATP created from the electrons
  being passed from Fd (Ferroredoxin) back thru the
  e.t.c. a 2nd time to make more ATP.
• Once the electrons are on Fd it can either pass
  them on to NADP or back to the e.tc. Different
  enzymes transfer the e- each way and which way
  each goes is dependent on which enzyme grabs the
  e- first. Therefore it is concentration
  dependent and about 50-50.

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Cyclic vs. Non Cyclic Photophosphorylation
cyclic
Non-cyclic
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Calvin Cycle
http//prezi.com/ied7qiqcxi9z/the-calvin-cycle/
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Calvin Cycle - Making Sugar
CO2 RuBP Hydrogens with high energy
electrons
5-Carbon Molecule
(from chlorophyll)
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RuBP Sugar
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Steps of the Calvin Cycle

• 1 molecule of CO2 is added to RuBP (5 C) by the
  enzyme RUBISCO forming a 6 carbon intermediate
  (Carbon Dioxide Fixation)
• The 6 carbon immediately breaks into 2 3-C
  phosphoglycerate
• ATP is used to add a P to each phosphoglycerate
• The high energy e- and H are then added from
  NADPH - making G3P
• As the G3P builds up, 5 G3Ps are reworked into 3
  RUBP (It takes 3 cycles to make 6 G3Ps so 5
  remake 3 RUBP and 3 RUBPs were used in 3 Calvin
  cycles)
• The one extra G3P not used for RUBP is a useable
  sugar and is converted to glucose etc.

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Summary Equation
Which part of the equation comes from the light
reactions and which parts are from the Calvin
Cycle?
Light
Chlorophyll
CO2 H2O ? Glucose O2
Light energy
Calvin
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Why Cant The Calvin Cycle Happen At Night?

• You need the high energy electrons from the light
  reactions and you cant get them without the
  light.
• The stomates close at night to conserve water and
  no CO2 is available
• Rubisco the enzyme that puts CO2 on RuBP is
  light sensitive.

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What Effects the Rate of Photosynthesis?

• Temperature
• Light Intensity
• CO2
• pH
• O2

Photorespiration O2 competitively inhibits
Rubisco so no CO2 can enter the Calvin cycle
therefore there is no photosynthesis and the CO2
is just given off
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Leaf and Cellular Adaptations to Hot Dry Climates

• C4 Plants
• Sugar Cane, Corn, Grass
• Different cellular arrangement in the leaf
• In mesophyll CO2 PEP (Pepco) form a 4C product
• Pepco isnt inhibited by O2
• The 4C product diffuses into the bundle sheath
  and releases the CO2
• Normal CO2 fixation by Rubisco in the bundle
  sheath

• CAM
• Cactus, succulents
• Open stomates at night and collect CO2
• CO2 binds to an organic acid which stores the CO2
• During the day when NADPH and ATP are made thru
  the light reactions, CO2 is released from the
  organic acid and the Calvin Cycle proceeds

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Leaf Structure of a C4 Plant
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C4 Pathway