Photosynthesis

• Stroma


  fluid portion of the chloroplast; outside of the thylakoids

  
• Function of the stroma

  contains enzymes, NADPH, and ATP to convert CO2 into carbohydrates
• Where do light-independent reactions take place?

  stroma of the chloroplast

  
• CO2 assimilation

  conversion of carbon dioxide to organic compounds
• How much CO2 is needed for photosynthesis?

  6, because glucose has 6 carbon atoms
• Calvin Cycle


  reactions of photosynthesis in which energy from ATP and NADPH is used to build high-energy compounds such as sugars

  
• Calvin cycle function


  to convert CO2 into G3P (glyceraldehyde-3-phosphate)
• What is G3P used for in the Calvin cycle?

  as a starting substrate in other metabolic pathways, such as the production of glucose and regeneration of RuBP
• 3 phases of calvin cycle

  carbon fixation, reduction, regeneration of RuBP

  
• Rubisco


  The most abundant protein on earth. Performs Carbon Fixation in the Calvin Cycle.
• Phase 1: Carbon Fixation


  CO2 combines with ribulose 1,5-bisphosphate to form an unstable 6-carbon molecule which breaks down into 2 molecules of 3-phosphoglycerate (PGA) (happens 6 times because each CO2 is brought in individually)

  
• C3 plants

  A plant that only uses the Calvin cycle to convert CO2

  
• Phase 2: Reduction

  ATP from cellular respiration breaks apart and the phosphate group attaches to PGA to form 1,3-bisphosphoglycerate. NADPH is then oxidized and gives electrons away producing Pi, and 1,3-bisphosphoglycerate is reduced as the electrons help remove the phosphate group to form G3P

  
• What happens to G3P after the calvin cycle?

  some leave the Calvin cycle to form glucose and other carbohydrates, while is stored in the roots so the plant can grow
• Phase 3: Regeneration of RuBP


  energy from ATP is used to break and reform bonds to make 6 RuBP from 10 G3P

  
• Other molecules that G3P synthesizes


  - sucrose

  - starch

  - cellulose

  - corn oil

  - safflower oil

  - olive oil

  - amino acids (combined with a source of nitrogen)
• Cellular respiration vs Photosynthesis

  Cellular respiration:

  - Occurs all the time

  - Occurs in mitochondria (mostly)

  - Requires O2 and releases CO2

  - NAD+ and FAD are electron carriers

  Photosynthesis:

  - Occurs only in light

  - Occurs in chloroplast

  - Requires CO2 and releases O2

  - NADP+ is an electron carrier

  
• The Z diagram

  A representation of the path of excited electrons through the photosystems, acceptors, and donors

  
• Photophosphorylation

  The process of generating ATP from ADP and phosphate using a proton-motive force generated by the thylakoid membrane of the chloroplast during the light reactions of photosynthesis.

  
• Step 1 of light dependent reactions

  Chlorophyll and other light-absorbing molecules in the thylakoid membrane absorb energy from sunlight

  
• What happens to the electron when the photon of light hits the antenna complex?

  it gets excited and the energy gets transferred to the reaction centre P680

  
• How does the P680 molecule replace its lost electrons?

  it becomes a strong electron attractor and breaks apart 2 water molecules stripping 4 electrons from it, releasing oxygen and the 4 H+ ions remain in the thylakoid space (can happen 200 times per second)
• What does P680 do?

  it gets excited and passes on its electron to a high-energy electron acceptor
• What do the electron carriers in Photosystem II do?

  they shuttle the high-energy electrons and the electrons release energy to go to the b6-f complex to pump H+ ions from the stroma into the thylakoid space to create a concentration gradient
• What happens after the electrons pass through the b6-f complex?

  it releases energy again as an electron carrier passes it onto Photosystem I
• What happens when the electrons get passed onto Photosystem I?

  a photon of light hits Photosystem I to excite it again, and the excited electron passes onto P700
• What does P700 do?

  it passes on the excited electrons to an electron acceptor

  
• How are the lost electrons replaced in photosystem I?

  they are replaced by the electrons that were passed from photosystem II
• What does the electron carrier from Photosystem I do?

  carries the electrons as they release energy, using the electron's energy for NADP reductase to reduce NADP+ into NADPH (no ATP required)
• How much does the passage of one electron pair produce?

  1 NADPH and slightly more than 1 ATP, however not enough to drive light-independent reactions
• How is chemiosmosis generated in photosynthesis?

  by pumping H+ ions through the b6-f complex

  
• cyclical photophosphorylation


  the electrons from the b6-f complex are passed onto Photosystem I, and instead of going to NADP reductase, they are passed back to the b6-f complex (no NADPH is produced)
• Why do plants perform cyclical photophosphorylation?

  if it needs more ATP for survival and has no water
• Photosynthesis

  the conversion of light/radiant energy from the sun into chemical energy

  
• Organisms that perform photosynthesis


  cyanobacteria, plants, and algae
• Photosynthesis equation

  6CO2 + 6H2O + light energy --> C6H12O6 + 6O2

  
• How do we have a symbiotic relationship with plants?

  since they go through photosynthesis, which is the opposite equation of cellular respiration, it shows that plants use water and CO2 to produce glucose, and humans consume glucose to go through cellular respiration
• Two reactions of photosynthesis

  light dependent and light independent

  
• light-dependent reactions

  reactions that use light energy to produce ATP and NADPH

  
• light-independent reactions

  ATP and NADPH are used to produce glucose (no light needed)