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Biochem 2 (CHEM 441B) > Ch. 12 > Flashcards

Ch. 12 Flashcards

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1
Q

What is photosynthesis?

A

Production of energy from sunlight

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2
Q

What is photooxidation?

A

Transfer of electrons from chlorophyll to electron acceptor

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3
Q

What is photooxidation important in?

A

Redox-based energy conversion

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4
Q

What happens in the photosynthetic electron transport system?

A

Light-absorbing pigment is photoexcited and transfers electron to another molecule as a result of photooxidation

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5
Q

What are the components of the photosynthetic electron transport system?

A
  • PSI
  • PSII
  • Cytochrome b6f
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6
Q

What is the Calvin cycle?

A

Metabolic pathway of carbon fixation
- Uses chemical energy (ATP and NADPH) to convert CO2 to triose phosphates and other carbs

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7
Q

Under what conditions is the Calvin cycle most active?

A

Most active under light (high ATP and NADPH levels)

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8
Q

What does the Calvin cycle produce?

A

Triose phosphates

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9
Q

What are triose phosphates used to make?

A

Hexose sugars

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10
Q

What are the steps of photosynthetic electron transport?

A
  1. 4 photons are absorbed by chlorophyll molecules in PSII
  2. Electron transport via carrier molecules in photosynthetic electron transport system; creates proton gradient across membrane
  3. 4 photons are absorbed by PSI
  4. Chloroplast ATP synthase produces ATP
  5. ATP and NADPH are used in enzymes in the Calvin cycle to drive carbon fixation
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11
Q

What are the membranes of a chloroplast?

A
  • Inner membrane (permeable)
  • Outer membrane (impermeable)
  • Thylakoid membrane (impermeable)
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12
Q

What is the thylakoid membrane the site of?

A

Photosynthetic electron transport system and ATP synthase complex

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13
Q

What the pH in the lumen?

A

pH = 5 (more acidic than stroma)

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14
Q

What is the pH in the stroma?

A

pH = 8 (less acidic than lumen)

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15
Q

Label the parts of a chloroplast.

A
  1. Thylakoid membrane
  2. Thylakoids
  3. Lumen
  4. Lamella
  5. Strong
  6. Granum
  7. Outer membrane
  8. Inner membrane
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16
Q

What does the change in pH from the stroma to the lumen cause?

A

Results in a proton gradient and ATP synthesis

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17
Q

What are chromophores?

A

Light-absorbing molecules found as part of photosensitive biological proteins/complexes

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18
Q

What is chlorophyll?

A

Primary chromophore in chloroplasts and cyanobacteria

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19
Q

How many electrons are required to oxidize 2 H2O into O2 + NADPH?

A

4 electrons

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20
Q

What is a photon?

A

Quantum of light energy

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21
Q

What is an exciton?

A

Quantum of energy passed from an excited molecule to another molecule

22
Q

What is free chlorophyll?

A

Upon excitation, absorbed energy is released as fluorescence and heat

23
Q

What is LHC-bound chlorophyll?

A

Upon excitation, exciton transfer occurs

24
Q

What are the 3 possible outcomes of photon absorption by cholorphyll?

A
  1. Resonance energy transfer
  2. Fluorescence
  3. Photooxidation
25
Q

What is resonance energy transfer?

A

Excited electron returns to ground state by transferring energy of excitation to a nearby molecule, causing that molecule to get excited

26
Q

What is resonance energy transfer important in?

A

“Harvesting” light energy

27
Q

What is a reaction center?

A

Specialized pair of chlorophyll molecules in PS that can convert photon energy to electrochemical energy via photooxidation

28
Q

What is the structure of a chlorophyll?

A
  • Mg2+ in the middle of the 4 nitrogen atoms of the pyrrole
  • Heterocyclic 5-ring system
  • Have a long tail (phytol)
29
Q

Why are chlorophylls highly effective photoreceptors?

A
  • Polyene: alternating single and double bonds
  • Strong absorption in visible light
  • Unusually high extinction coefficient
  • Good for absorbing light during photosynthesis
30
Q

What are photosystems?

A

Functional arrays of light-absorbing pigments

31
Q

What are light-harvesting complexes (LHCs)?

A

“Solar panels” that capture light for photooxidation

32
Q

Are there more LHCI or LHCII?

A

LHCII

33
Q

What is the PSII reaction center?

A

P680

34
Q

What is the PSI reaction center?

A

P700

35
Q

What is the Z scheme?

A

Describes the complete route of electron flow from H2O to NADP+

36
Q

Calvin cycle equation

A

2H2O + 2NADP+ + 8 photons –> O2 + NADPH +2H+

37
Q

What does phosphorylation generate?

A

ATP

38
Q

Where does CO2 assimilation occur?

A

In the stroma via the Calvin cycle

39
Q

What is the key intermediate in CO2 assimilation?

A

Ribulose-1,5-BP

40
Q

What is RUBISCO?

A

Enzyme involved in the first major step of CO2 fixation

41
Q

What does CO2 assimilation produce?

A
  • 3-phosphoglycerate
  • G3P and DHAP (in equilibrium)
42
Q

What is the net result of CO2 assimilation?

A

Reduction of CO2 with NADPH

43
Q

What are the metabolites of CO2 assimilation (3-phosphoglycerate, G3P, DHAP) used to make?

A
  • Fructose-1,6-BP
  • Fructose-6-P
44
Q

What are the 3 stages of the Calvin cycle?

A
  • Stage 1: fixation of CO2 into 3-phosphoglycerate by RUBISCO
  • Stage 2: reduction of 3-phosphoglycerate to form hexose sugars
  • Stage 3: regeneration of ribulose-1,5-bisphosphate (carbon shuffle)
45
Q

What 3 mechanisms control the activity of Calvin cycle enzymes?

A
  1. Enzyme inhibitor (CA1P) blocks RUBISCO activity
  2. RUBISCO and F-1,6-bisphosphate are activated by increased pH and increaed [Mg2+] which occurs in light
  3. Some enzymes are reduced by a small protein called thioredoxin (redox protein)
46
Q

What is photorespiration?

A

Costly side reaction of photosynthesis due to the lack of RUBISCO specificity

47
Q

What are the building blocks for the 3 primary carbohydrates?

A

Hexose phosphates

48
Q

Why is RUBISCO not a good enzyme?

A

Its kcat = 3 while other enzymes are generally around kcat = 1000
- Only 3 molecules of CO2 fixed per second per molecule of RUBISCO at 25ºC

49
Q

What does photosynthesis accomplish for the cell?

A

Converts light to redox energy –> generates ATP –> reduces NADP+ to NADPH

50
Q

What are the overall net reactions of photosynthesis?

A
  • Photosynthetic electron transport system
    2H2O + 8 photons + 2NADP+ + ~3ADP + ~2Pi –> O2 +2NADPH + ~3ATP
  • Calvin cycle
    3CO2 + 6NADPH + 9ATP + 6H2O –> G3P + 3RuBP + 6NADP+ + 9ADP + 9Pi
51
Q

What are the key enzymes in photosynthesis?

A

Photosynthetic electron transport system
- Cytochrome b6f

Calvin cycle
- RUBISCO

Biochem 2 (CHEM 441B) (23 decks)

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