The light-dependent reactions in plants Flashcards

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1
Q

Where do light-dependent reactions occur?

A

-In the membranes

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2
Q

In Photosynthetic bacteria what is their photosynthetic membrane?

A

-The plasma membrane itself

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3
Q

Why is the thylakoid membrane important?

A

-Bc it contains structures that are involved in light-dependent reactions which is they are called Thylakoid reactions

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4
Q

What are the 4 stages of thylakoid reactions?

A
  • Primary photoevent
  • Charge separation
  • Electron transport
  • Chemiosmosis
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5
Q

What is the Primary Photoevent stage of Thylakoid reactions?

A

-This is where a photon of light is captured by a pigment & excites an electron within the pigment

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6
Q

What is the Charge Separation stage of Thylakoid reactions?

A

-The excitation energy from the electron is transferred to the reaction center by transferring an energetic electron to an acceptor molecule= initiates electron transport

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7
Q

What is the Electron Transport stage of Thylakoid reactions?

A
  • This is where the excited electrons are shuttled along a series of electron carrier molecules embedded within the photosynthetic membrane
  • Some of these molecules react by transporting membrane protons across the membrane= generates a proton gradient
  • The electrons are then reduced to NADPH
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8
Q

What is the Chemiosmosis stage of Thylakoid reactions?

A

-The protons that accumulate on one side of the membrane now flow back across the membrane through ATP synthase= where chemiosmotic synthesis of ATP takes place

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9
Q

What are the 2 stages of the Light-dependant reactions?

A
  • The first stage is the capturing energy from light which makes up stage 1-3 for the thylakoid reactions
  • The 2nd stage is the generation of ATP which is the 4th stage of the thylakoid reactions
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10
Q

What is Cyclic Photophosphorylation?

A
  • That a single photosystem in purple & green bacteria is used to generate ATP via electron transport & that process returns the electrons back to the reaction center
  • These systems are Anoxygenic
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11
Q

What is the peak absorption for purple nonsulfur bacteria?

A
  • It occurs at a wavelength of 870nm= not visible to the human eye
  • which is why they use the pigment P870 in the reaction center
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12
Q

What happens when P870 reaction center absorbs a photon?

A

-The excited electron is passed to an electron transport chain that passed the electrons back to the reaction center= generates a proton gradient for ATP synthesis

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13
Q

What is the peak absoprtion for the green sulfur bacteria?

A

-It occurs at a wavelength of 840nm

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14
Q

What happens to the green sulfur photosystem?

A
  • Excited electrons can either be passed to NADPH or returned to chlorophyll by an electron transporter chain (like the one in purple bacteria)
  • Then use electrons from hydrogen sulfide to replaced those passed to NADPH
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15
Q

What do the proteins for the purple bacterial photosystem appear to be homologous with?

A

-The proteins are homologous to the proteins in the modern photosystem II

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16
Q

What do the proteins for the green bacterial photosystem appear to be homologous with?

A

-The proteins are homologus to the proteins in the modern photosystem I

17
Q

What do the photosystem of purple & green bacteria have in common?

A
  • They both don’t generate sufficient oxidizing power to oxidize H2O
  • They are both anoxygenic & anaerobic
18
Q

Why is having 2 linked photosystems better than having the cyclic photophosorylation?

A
  • The linked systems aren’t as limiting like the cyclic one
  • It provides an alternative source of electrons from the oxidation of water which also generates O2= oxygenic photosynthesis
  • The transfer of electrons also produces NADPH= can be used in biosynthesis of carbs
19
Q

What are the 2 photosystems for plants?

A
  • Photosystem I

- Photosystem II

20
Q

What is the absoption peak of Photosystem I?

A
  • The peak is 700nm

- So its reaction center pigment is P700

21
Q

What is Photosystem I?

A
  • It can pass electrons to NADP+ which produces NADPH

- The electrons lost are replaced by electrons from Photosystem II

22
Q

What is the absoprtion peak of Photosystem II?

A
  • The peak is 680nm

- So its reaction center pigment is P680

23
Q

What is Photosystem II?

A

-It can generate an oxidation potential high enough to oxidize water to replace the electrons transferred to Photosystem I

24
Q

What happens when Photosystem I & II work together?

A

-They carry out a transfer of electrons that generate both ATP & NADPH

25
Q

How is Photosystem I & II connected?

A

-They are connected by the electron carriers= Cytochrome/b6-f complex

26
Q

What is the Cytochrome/b6-f complex?

A
  • It connects photosystem I & II together
  • This complex can use energy from the passage of electrons to move protons across the thylakoid membrane to generate the proton gradient used by ATP synthase enzyme
27
Q

LEFT OFF

A

P 157