Dark Reactions

• PCR - photosynthetic carbon reduction
• PCR — Process where inorganic carbon is converted to organic compound
• 3 Biochemical variants of PCR

  • Calvin-benson cycle
  • Hatch and slack pathway
  • Crassulacean acid metabolism pathway
• C3 – calvin-benson cycle
• C4 - hatch and slack pathway
• CAM - crassulacean acid metabolism pathway
• Fundamental carboxylating mechanism in plants resulting to a net fixation of CO2

  C3
• What is the 1st stable product and reason for the name C3 cycle?

  3-phosphoglyceric acid (PGA)
• Carboxylation is catalyzed by RuBisCO
• RuBisCO - Ribulose Biphosphate Carboxylase/Oxygenase
• World's most abundant enzyme, up to 50% of the total soluble protein in a leaf

  RuBisCO
• Carboxylase: fixes CO2 into RuBP
• Oxygenase: condenses O2 with RuBP
• C3: 1 CO2 = 3 ATP, 2 NADPH
• C3 Product = 3-C sugar gluceraldehyde-3-phosphate (G3P) or triose phosphate (TP)
• 8 CO2 = 24 ATP, 16 NADPH
• All plants perform this cycle

  C3 cycle
• Can C3 plants perform C4?

  No
• 3 stages of C3 cycle

  • Carboxylation
  • Reduction
  • Regeneration
• Photorespiration - a process that occurs in plants and some bacteria that converts glucose into lactate
• 2-C compound that is rapidly converted to glycolate and subsequently metabolized in the process

  Phosphoglycolate
• PCO cycle

  C2 photorespiratory carbon oxidation
• Process wherein RuBisCO oxygenates RuBP

  PCO cycle
• T or F: Does PCO cycle occur in green tissues in response to high CO2:O2 ratios

  False
• T or F: Does photorespiration occur more at high temperature and high irradiance?

  True
• T or F: the reason for the occurrence of photorespiration

  The substrate specificity of RuBisCO shifts in favor of O2 as temperature rises

  True
• T or F: the reason for the occurrence of photorespiration

  Leaf CO2 concentration ([CO2]) becomes very low at high irradiance largely due to rapid photosynthesis and low [CO2] favors oxygenation

  True
• T or F: Photorespiration requires the cooperative interaction of chloroplast, peroxisome, and mesophyll

  False
• T or F: RuBisCO fixes CO2 3.4x more than O2

  True
• This pathway salvages 75% of the carbon from glycolate from the C2 cycle and 25% of the carbon is lost

  PCO cycle
• T or F: at higher temperature solubility of carbon dioxide decreases

  True
• T or F: reason for the importance of photorespiration

  Internal cellular recycling of 3 gases: CO2, O2, and NH3

  True
• T or F: reason for the importance photorespiration

  Glycolate can decrease levels of oxygen hence oxidative photodestruction of photosynthetic apparatus is prevented particularly during high irradiance

  True
• T or F: reason for the importance photorespiration

  Physiological defense against high irradiance and thermal load excess -> ATP and NADPH are used by the process -> excess photochemical energy is dissipated

  True
• T or F: reason for the importance of photorespiration

  Contribution to cell amino pool (glycine and tyrosine)

  False
• T or F: reason for the importance of photorespiration

  Response to niche diversification scheme

  True
• T or F: Photorespiration does not occur in many plants

  True
• T or F: Angiosperms have 2 types of carbon assimilation pathway exhibiting CO2 concentrating mechanism: C3 cycle and CAM cycle

  False
• CCM - CO2-concentrating mechanism
• T or F: plants in desert environments do C4 photosynthetic carbon fixation

  False