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Advanced Biochem > Photosynthesis > Flashcards

Photosynthesis Flashcards

1
Q

Autotroph

A

Carbon source from atmospheric carbon dioxide

Plants, cyanobacteria, algae

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2
Q

Heterotroph

A

Carbon source from organic compounds

Animals, most bacteria

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3
Q

Energy yielding oxidation of glucose

A

C6H12O6 + 6 O2 –> 6 CO2 + 6 H2O + energy

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4
Q

Site of oxidative phosphorylation in eukaryotes

A

Inner mitochondrial membrane

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5
Q

Number of oligomeric assemblies of proteins associated with oxidative phosphorylation, found in the inner mitochondrial membrane

A

5

Complex I, II, III, IV, & V

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6
Q

Complex V in ETC

A

ATP synthase

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7
Q

Site of photosynthesis in eukaryotes

A

Chloroplast

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8
Q

Where is ATP synthesized in mitochondria?

A

Mitochondrial matrix

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9
Q

Where is ATP synthesized in chloroplasts?

A

Stroma

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10
Q

Stroma

A

Outside of thylakoid membrane

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11
Q

Lumen

A

Inside of thylakoid membrane

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12
Q

Light Reactions

A

Generate energy-rich NADPH and ATP at the expense of solar energy

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13
Q

Dark Reactions

A

NADPH and ATP are used to form triodes and more complex compounds (glucose) from CO2 and H2O

Carbon assimilation

Can happen in dark or light

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14
Q

Who is the reducing agent in the given reaction?

CO2 + H2O —light—> (CH2O) + O2

A

H2O is the reducing agent

CO2 is reduced

Gain H = reduced

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15
Q

General Reaction

A

CO2 + 2 H2A —light—> (CH2O) + 2A + H2O

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16
Q

Photoreceptors

A

Light absorbing molecules

Absorb light in the visible region

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17
Q

Energy of Photon

A

E = hv = (hc)/y

v = frequency
c = speed of light (3 x 10e8 m/s)
y (lambda) = wavelength

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18
Q

Principle photoreceptor

A

Chlorophyll

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19
Q

Accessory Pigments in Plants

A

B-carotene
Lutein (xanthophyll)

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20
Q

Antenna Pigments in Cyanobacteria and Red Algae

A

Phycoerythrobilin
Phycocyanobilin

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21
Q

Different fates of excited electrons

A

Produce heat
Fluorescence
Exciton Transfer (resonance energy transfer)
Photooxidation

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22
Q

Antenna chlorophylls in light harvesting centers (LHC) pass the energy randomly, by exciton transfer until it traps by reaction center (RC) chlorophyll

A
23
Q

Out of many pigments, only chlorophyll molecules associated with RC can transduce light into chemical energy. The other pigment molecules are called ____

A

Antenna molecules

Accessory pigments and other chlorophylls

24
Q

Which of the following is the site of ATP synthesis in chloroplasts?

Outer membrane
Inner membrane
Stroma
Thylakoid membrane
Thylakoid compartment

A

Stroma

ATP synthase is in the thylakoid membrane, but ATP is produced into the stroma

25
Q

Light Harvesting Centers (LHCs)

A

Transmembrane proteins

26
Q

Functions of Accessory Pigments

A
  1. Harvest light energy and transfer them to nearby chlorophyll similar to the chlorophylls
  2. Prevent oxidation of chlorophylls which results in producing free radicals
27
Q

Photosynthetic Reaction Centers (RCs)

A

Transmembrane protein containing a variety of chromophores

28
Q

How are RCs named?

A

Based on the wavelength of light they absorb

Ex. P870 absorbs light at 870 nm

29
Q

Bacteriopheophytin vs Bacteriochlorophyll

A

Bacteriopheophytin does not have an Mg in the center

30
Q

Antenna chlorophylls and other accessory pigments…

A

Absorb light energy, transferring it between molecules until it reaches the RC

31
Q

Reaction Center

A

Photochemical reaction here converts the energy of a photon into a separation of charge, initiating electron flow

32
Q

Photosynthesis RC: Step 1

A

Light excites an antenna molecule (chlorophyll or accessory pigment), raising an electron to a higher energy level

33
Q

Photosynthesis RC: Step 2

A

The excited antenna molecule passes energy to a neighboring chlorophyll molecule (resonance energy transfer), exciting it

34
Q

Photosynthesis RC: Step 3

A

The energy is transferred to a reaction-center chlorophyll, exciting it

35
Q

Photosynthesis RC: Step 4

A

The excited reaction-center chlorophyll passes an electron to an electron acceptor

36
Q

Photosynthesis RC: Step 5

A

The electron hole in the reaction center is filled by an electron from an electron donor

37
Q

Result of Photosynthesis RC

A

The absorption of a photon has caused separation of charge in the reaction center

38
Q

Bacterial Photosystem I (PSI)

A

Type I reaction center

Present in heliobacteria and green sulfur bacteria

39
Q

Bacterial Photosystem II (PSII)

A

Type II reaction center

Present in purple bacteria and green filamentous bacteria

40
Q

Photosystems in Cyanobacteria

A

Both PSI and PSII couple in series

Cyanobacteria: most abundant class of photosynthetic bacteria

41
Q

Photosystem II

A

Cyclic

Makes proton gradient across membrane to synthesize ATP

42
Q

Photosystem II Reactions Sum

A

2 photons + 4 H+ (in) —> 4 H+ (out)

43
Q

Photosystem I

A

Usually noncyclic

Reduces NADP+ to NADPH

Green sulfur bacteria: electrons are transferred from H2S or S2O3(2-)

44
Q

When is Photosystem I cyclic?

A

If more energy is required for biosynthesis reactions (need more ATP)

No NADPH is made

45
Q

Most photosynthetic bacteria have one type of reaction center, but cyanobacteria and algae have:

A

Two photosystems that work in tandem

46
Q

Tandem Photosystems

A

PSI: Light excites P700 electron
(lower reduction potential, donates electrons to higher reduction potential)

PSI: P700 becomes electron deficient

PSI: NADP+ is reduced to NADPH (noncyclic, needs 2 electrons to reduce)

PSII: Light excites P680 electron
(lower reduction potential, donates electrons to higher reduction potential)

PSII: P680 becomes electron deficient

PSII: Proton gradient is formed, electron donated to P700

PSII: P680 accepts electron from H2O –> 1/2 O2

47
Q

ETC Complex IV

A

1/2 O2 + 2H+ + 2e- —> H2O
Eº’ = 0.82

High reduction potential
Good oxidizing agent
Likes to be reduced

48
Q

In photosynthesis, reverse reaction takes place

A

H2O —> 1/2 O2 + 2H+ + 2e-

2 P+(680) + 2 e- —> 2 P(680)
Eº’ = higher than O2

49
Q

NADP+ + 2e- + H+ —> NADPH

A

Need 2 photons in PSI & PSII (4 total)

H2O splitting gives 2 e- to produce 1/2 O2

4 H+ (in cyt b6f) + 2 H+ (water splitting) = 6 H+ increase in lumen
≈ 2 ATP

50
Q

What is produced in the stroma?

A

ATP
NADPH

51
Q

What is produced in the lumen?

A

H+

52
Q

Most cyanobacteria contain a complex internal network of membranes where ______ are located:

A

Photosystem complexes

53
Q

Photosystem II of the cyanobacteria Synechococcus elongates

A

The monomeric form of the complex has two major transmembrane proteins, D1 and D2

Although the two subunits are nearly symmetric, electron flow occurs through only one of the two branches of cofactors (on D1)

54
Q

Water-splitting activity of the oxygen-evolving complex

A

The sequential absorption of four photons (excitons), each absorption causing the loss of one electron from the Mn center, produces an oxidizing agent that can remove four electrons from two molecules of water, producing O2.
The electrons lost from the Mn center pass one at a time to an oxidized Tyr residue in a PSII protein, then to P680+

Advanced Biochem (4 decks)

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