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Bio II > Lecture 16: Photosynthesis (Part 2) > Flashcards

Lecture 16: Photosynthesis (Part 2) Flashcards

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1
Q

What are photosystems?

A
  1. Units of structure and function for the light reactions in chloroplasts
  2. They carry out the light reactions
  3. made of complexes and pigments
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2
Q

What are the complexes in photosystems?

A

A. Antenna Complex
B. Reaction Center Complex

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3
Q

What is the antenna complex of the photosystem composed of?

A

chlorophyll and accessory pigment molecules.

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4
Q

What is the antenna complex’s function?

A

to gather light energy and pass it on to neighbouring pigments by resonance energy transfer.

Energy is transferred inside the antenna complex, from one molecule to the next, until it reaches the reaction center.

(notice it’s by transfer, not transformation)

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5
Q

What happens in the reaction center complex?

A

energy is transferred and an electron in two specialized chlorophyll a molecules (special pair) is excited.

The photoexcited electron is then transferred to a primary electron acceptor (photochemical reduction).

The electrons in the oxidized reaction center are replaced by an electron donor.

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6
Q

What energy transformation happens in the reaction center complex?

A

Electromagnetic energy is transformed to chemical energy.

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7
Q

Are the terms energy transfer and electron transfer the same? In what two complexes do each happen in photosystems?

A

No they are not the same;

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8
Q

What happens to the primary electron acceptor of the photosystem after it receives the electrons?

A

reduced primary electron acceptor of the
photosystem donates the electron to an ETC.

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9
Q

What does the ETC do after it receives electrons from the primary electron acceptor of the photosystem?

A

The ETC can either:
A. help make ATP by
chemiosmosis
B. trap the high energy
electron in NADPH

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10
Q

How many photosystems do oxygenic phototrophs have? What are they?

A

two types:

  1. Photosystem I (PSI)
  2. Photosystem II (PSII)
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11
Q

What is the collaborative work of PSI and PSII?

A

they work together in a Z-scheme

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12
Q

Where do most of our knowledge on each photosystems come from?

A

from studying anoxygenic photosynthetic bacteria that use either photosystem I or II only.

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13
Q

How does energy change in the z scheme?

A

the z scheme follows energy change as electrons are transferred in the light reactions

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14
Q

Where do you find a pair (dimer) of P680 chlorophyll molecules?

A

in the P680 reaction center of PSII

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15
Q

What does the number in P680 chlorophyll stand for?

A

It has a maximum absorbance at 680 nm

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16
Q

Where do you find a pair (dimer) of P700 chlorophyll molecules?

A

in the P700 reaction center of PSII

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17
Q

What is this image and analogy of?

A

the z scheme

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18
Q

What does photosystem II do?

A

produces ATP by photophosphorylation

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19
Q

What doe PSII require to do photophosphorylation?

A
  1. An ETC that produces a proton concentration gradient .
  2. ATP synthase that produces ATP .
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20
Q

Where is the ETC of PSII located?

A

in the thylakoid membrane.

21
Q

What is the ETC of PSII composed of?

A

The ETC includes plastoquinone (PQ), which shuttles electrons from the primary electron
acceptor in the thylakoid membrane to a cytochrome complex.

22
Q

What happens to the electrons that participate in the ETC?

A

Since they participate in redox reactions, they gradually step down in potential energy

23
Q

What does the redox reactions in ETC allow?

A

result in protons being pumped from one side of the membrane to the other and creating an H+ concentration gradient called a proton motive force (PMF).

24
Q

What does the flow of protons down their concentration gradient through ATP synthase causes it to do?

A

to rotate, change its shape, and promote the enzymatic activity that drives the phosphorylation of ADP to produce ATP.

25
Q

Where does the chemical energy in ATP comes from?

A

The energy of the electrochemical gradient produced by the ETC is used to produce the chemical energy in ATP.

26
Q

Where did the energy to build the electrochemical gradient come from?

A

comes primarily from the absorption of light energy by chlorophyll and other pigment molecules in the photosystems. (photon excite electrons etc)

27
Q

What does photosystem I do?

A
  • Photosystem I produces the reduced electron carrier NADPH.
28
Q

What enzyme does photosystem I require to produce NADPH?

A

NADP+ reductase

29
Q

What is NADPH?

A

Energy intermediate that is an electron carrier. (Similar in function to the NADH and FADH2 produced during cellular respiration.)

30
Q

What about the reduction potential of NADPH?

A

NADPH has a high reduction potential that can donate electrons to other compounds and reduce them.

31
Q

What is the general structure to recognize for NADPH?

A

Dinucleotide: two nucleotides linked together.

32
Q

How does photosystem II replace electrons lost?

A

PSII splits water and transfer its electrons to the P680 reaction center

33
Q

What allows PSII to split water to obtain electrons?

A

When excited electrons leave the reaction center of photosystem II, the reaction center becomes so electronegative that it can remove electrons from water and oxidize it.

34
Q

What is oxygenic photosynthesis?

A

photosynthesis where an enzyme complex splits water to replace lost electrons and create molecular oxygen as a byproduct

35
Q

What is the only enzyme complex capable of oxidizing water like in oxygenic photosynthesis called?

A

Oxygen Evolving Complex (OEC)

36
Q

In which photosystem is the OEC part of?

A

PSII

37
Q

What is this?

A

Oxygen Evolving Complex (OEC)

(3-D structure determined in 2004 using x- ray crystallography and mechanism is being studied.)

38
Q

What is the OEC?

A
  • a protein complex in the thylakoid membrane that contains a group of metal ion cofactors (manganese cluster).
  • It has enzymatic activity that can split water.
39
Q

Name all components of the trajectory of electron flow

A
40
Q

What is Pc?

A

Plastocyanin (Pc) is a peripheral membrane protein (within thylakoid space) that accepts electrons from the ETC of PSII and donates electrons to photosystem I. It physically links the two photosystems in the Z scheme.

(acts as a shuttle)

41
Q

To which photosystem are Pq and Fd part of? What are their complete names?

A
42
Q

Which three processes contribute to the H+ electrochemical gradient?

A
  1. splitting of water
  2. chimiosmosis
  3. reduction of NADP+ to NADPH
43
Q

Where do the electrons from water end up at the end of the light reactions?

A

In NADPH

44
Q

What is the purpose of producing ATP and NADPH?

A

to power the Calvin Cycle (production of sugars)

45
Q

What is the equivalent of the Quinone (mitochondrion’s ETC) in chloroplasts?

A

the plastoquinone

46
Q

What is the equivalent of cytochrome C (mitochondrion’s ETC) in chloroplasts?

A

the plastocyanin

47
Q

What is cyclic photophosphorylation?

A
  • Fd transfers electrons to ETCII instead of NADP+.
  • produces additional ATP instead of NADPH.
  • Coexists with the Z-scheme in chloroplasts.
48
Q

Does cyclic photophosphorylation produce molecular oxygen?

A

No because in cyclic photophosphorylation, only photosystem I (PSI) is involved, and it does not include the water-splitting step that releases molecular oxygen, as seen in noncyclic photophosphorylation.

49
Q

Why does cyclic phosphorylation exist?

A
  1. ATP Production: beneficial when the cell requires more ATP for processes such as the Calvin cycle or cellular respiration than it needs NADPH for biosynthetic reactions.
  2. Adaptation to Environmental Conditions: such as low light intensity or high temperatures, where the demand for ATP is higher compared to NADPH. (cell to optimize its energy production based on its immediate needs)
  3. Maintenance of ATP/NADPH Balance (when there is too much NADH produced by noncyclic photophosphorylation)
  4. Conservation of Water: no splitting of water involved, useful in environments where water availability is limited, such as arid or drought conditions

Bio II (21 decks)

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