Photosynthesis
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PHOTOSYNTHESIS. Converts light energy into chemical energy through a complex series of biochemical reactions 6CO 2 + 6H 2 O -> C 6 H 12 O 6 + 6O 2 Photosynthesis occurs inside the chloroplasts

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Photosynthesis
PHOTOSYNTHESIS

  • Converts light energy into chemical energy through a complex series of biochemical reactions

  • 6CO2 + 6H2O -> C6H12O6 + 6O2

  • Photosynthesis occurs inside the chloroplasts

  • White light from the sun is composed of different colors of different wavelengths – visible spectrum


Chloroplast structure
CHLOROPLAST STRUCTURE

  • Outer, double membrane

  • Inner Membrane system:

    • THYLAKOIDS – flattened sacs

    • GRANA – stacks of thylakoids

  • Light harvesting pigments embedded in thylakoid membrane

  • Surrounding thylakoids, liquid: STROMA



Light dependent rxns
LIGHT DEPENDENT RXNS (absorbs light in the blue-violet and orange-red and reflects light in green region

  • Visible light (traveling in “photons”, packets of energy) is changed into chemical energy

  • H2O is split into O2 and H

  • PS I and II absorb light energy

  • This light energy is transferred to reaction center, a Chlorophyll a that donates e- to electron carrier


Light dep rxns cont d
LIGHT DEP. RXNS cont’d (absorbs light in the blue-violet and orange-red and reflects light in green region

  • Lost e- from PSII is replaced by e- from H2O

  • At end of electron flow, electrons combine with NADP+ to form NADPH

  • As electrons flow along electron transport chain, protons build up inside thylakoids


H3C H (absorbs light in the blue-violet and orange-red and reflects light in green region

C1

"/,

H C C H CHJ H CH3 H H H H H C CH1

J,,/HJI I I I I I I I II! I

/c, /C"", /c""' /C, /C, /C""' /c, /C"", /c~ /c, /c" /CH1

H1C C C C C C C C C C C /C"

I I I I I I I I I I H3C CHJ

H1C, /C H H H H H CHJ H CH3 H

C "

H1 CH3

f,'-carotene


Light dep rxns cont d1
LIGHT DEP. RXNS cont’d (absorbs light in the blue-violet and orange-red and reflects light in green region

  • These built up protons will diffuse down concentration gradient through ATP synthase

  • TAH-DAH!! ATP is made!!!

  • PRODUCTS:

    • O2, ATP and NADPH!!!!


Calvin cycle
CALVIN CYCLE (absorbs light in the blue-violet and orange-red and reflects light in green region

  • Pathway that produces organic compounds, using energy stored in ATP and NADPH from the light reactions

  • Occurs in the stroma

  • CO2 is “fixed” into organic compounds

  • RuBP (ribulose bisphosphate) is the 5 carbon sugar that CO2 is bound to by the enzyme rubisco


More calvin
More CALVIN… (absorbs light in the blue-violet and orange-red and reflects light in green region

  • The new 6 carbon molecule is immediately split into 2 3-carbon molecules (PGA)

  • PGA converted to PGAL by addition of the phosphate from ATP and the hydrogen from NADPH

  • ADP, NADP+ and phosphate are used again in the light reactions to form more ATP and NADPH


  • To make one molecule of G3P, three turns of the cycle + 3 CO (absorbs light in the blue-violet and orange-red and reflects light in green region2 molecules

  • CO2 is fixed to RuBP by rubisco – produces unstable intermediate -> 3-phosphoglycerate

  • RuBP is regenerated – one per each trip through the cycle

  • Uses 9 ATP and 6 NADPH


Alternative pathways
ALTERNATIVE PATHWAYS (absorbs light in the blue-violet and orange-red and reflects light in green region

  • Calvin cycle plants = C3 because of PGAL that is formed (3 carbon)

  • Water loss through stomates is big problem

  • When air is hot and dry, stomates close to prevent water loss

  • BAD THING – CO2 levels fall and O2 levels rise, resulting in carbon fixation inhibition


C 4 pathway
C (absorbs light in the blue-violet and orange-red and reflects light in green region4 PATHWAY

  • During hottest part of day, C4 plants partially close stomates

  • A special enzyme fixes CO2 into 4-carbon compounds that is stored in bundle sheath cells and can then enter the Calvin cycle

  • Corn, sugar cane and crabgrass


Cam photosynthesis
CAM Photosynthesis (absorbs light in the blue-violet and orange-red and reflects light in green region

  • Adaptation to hot, dry climates

  • Open stomates at night and close them during the day (minimizes water loss)

  • CO2 that enters at night is fixed into a variety of organic compounds and stored in vacuoles; in morning, stomates close and CO2 is then released during the day and enters Calvin cycle

  • These plants grow very slowly – cactuses, pineapples


Rates of photosynthesis
Rates of Photosynthesis (absorbs light in the blue-violet and orange-red and reflects light in green region

  • 4 limiting factors:

    • Light intensity, temperature, [CO2], [O2]

      Active site of Rubisco can bind to O2 or CO2: Photorespiration – results in release of previously fixed CO2 that would otherwise remain in organic form


Rates of photosynthesis1
RATES OF PHOTOSYNTHESIS (absorbs light in the blue-violet and orange-red and reflects light in green region

  • As light intensity increases, so does rate of photosynthesis

  • Levels off at a max rate, when all electrons are excited

  • Same thing for CO2 levels

  • Temperature increase, rate increases to a point; then, enzymes denature and stomates close to prevent water loss, thus decreasing rate at high temperatures


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