Lecture 1/31

Question 1

How many PS does anoxygenic/oxygenic photosynthetic organisms have?

Answer 1

Anoxygenic - 1

Oxygenic - 2

Question 2

Why would you want PS and light reactions to occur in membranes?

Answer 2

You want a membrane because you want to set up a proton gradient (this drives ATP synthase)

Question 3

What do membranes in chloroplasts tell us?

Answer 3

These membranes in chloroplasts record endosymbiotic events that occur in cyanobacteria to an organelle.

Question 4

How does a cyanobacteria become a chloroplast?

Answer 4

Through a series of endosymbiosis.

Question 5

Why would you want to split water? What are its advantages?

Answer 5

Because water is everywhere.

Advantage of oxygenic

• electron donor is everywhere
• you are creating something that is toxic to everyone

Question 6

What two experiments were done to dissect the parts of the light reaction? What did they do?

Answer 6

“Red drop effect” - longer wavelengths of light have insufficient energy to drive photosynthesis.

“Enhancement effect” - showed far-red light and red light, measured oxygen production, and when both were shone, photosynthesis increased. Two photosystems were acting independently.

Question 7

Where are the photosystems located? In what part of the chloroplast?

Answer 7

Stroma lamellae - site of PS1
Grana lamellae (stack of thylakoids) - Site of PS2

They are spatially separated

Question 8

What is the spatial organization of the protein complexes in Ps?

Answer 8

PS2 is in staked regions of thylakoid membranes, surrounded by LHC
PS1 and ATP synthase poke out into the stroma.
Cyt b6f (part of the e- transport chain) is evenly distributed.
–shuttles e- from PS2 to PS1

Question 9

What wavelength does PS2 and PS1 absorb?

Answer 9

PS2 - P680

PS1 - P700

Question 10

Describe the oxygenic photosynthesis

look at Z-scheme, memorize diagram

Answer 10

In PS2, RC is surrounded by LHC. It’s hit by red light, PS2 gets activated.
It pulls an e- off water, creating O2.
Energy level goes up
passes the e- down the electron transport chain to PS1
PS1 gets hit by far-red light, gets even more activated and it generates a reducing power to reduce NADP

Question 11

What does ferredoxin NADP reductase (FNR) do?

Answer 11

Reducing power to reduce NADP+ to NADPH

• completes the electron transport chain that began with WOC.
• last stop of the train.

Question 12

What are the two really important features of PS2? Why are they important?

Answer 12

The water oxidizing complex (WOC) and the D1 protein.
WOC is one of the most important pieces of biochem that ever evolved. It does the splitting of water.
D1 protein binds the reaction center to chlorophyll and is easily damaged. When there’s too much light, D1 breaks. It’s always under repair.

PS2 also generates protons for ATP synthase.

Question 13

What is the significance of having manganese in WOC?

Answer 13

Depending on redox state of the ocean, Mn can be soluble or insoluble. This shows that a key part of the mechanism is REDOX SENSITIVE to the environment.
It also strops 4e- and 4H+ from water.

Question 14

What constitutes the path to the reaction center?

Answer 14

A huge network of hydrogen bonds make a path for tyrosine to the reaction center.

Question 15

What are the end products of photosynthesis?

Answer 15

• ATP
• Reducing power in NADPH
• oxygen

Question 16

What does Cyt b6f do?

Answer 16

It is an electron shuttle between PS2 and PS1.

• four protons are transported across the membrane for every two electrons.
• part of the electron transport chain (which is linear)

Question 17

What are some of the key features in PS1?

Answer 17

• Has Fe-S at its core.

- P700

Question 18

What is ferredoxin?

Answer 18

It is an iron-sulfur protein. Electrons are passed to ferredoxin from PS1.

Question 19

Why is the electron transport chain said to be a point of vulnerability?

Answer 19

Some herbacides work by quenching electron transport.
Quenching means soaking up the electrons before reaching PS1.
Eg DCMU and Paraquat

Question 20

Where is ATP synthesized?

Answer 20

By ATP synthase

Question 21

What is photoinhibition?

Answer 21

When there is too much light and reduces the plant’s growth

Question 22

How is PS2 damaged and what is damaged?

Answer 22

PS2 can be damaged from too much light.

D1 protein gets damaged

Question 23

How is PS1 damaged and what gets affected?

Answer 23

PS1 can be damaged from oxygen radicals it can cause a redox change to the FeS at its core.

Question 24

What is suppression?

Answer 24

Xanthophyll grab protons and energy which allows antenna proteins to release more heat before damage can occur.

Question 25

What are two ways to deal with photoinhibition?

Answer 25

Suppression - xanthophyll grab protons and energy to allow antenna proteins to release more heat before damage can occur
Scavenging - superoxide dismutase grabs oxygen radicals and protects the cell an antioxidant

Question 26

What is an example of scavenging?

Answer 26

D1 protein which gets consistently replaced in PS2

Question 27

Why is there so many ways to protect the plant from prohibition?

Answer 27

Because chl biosynthesis is energetically expensive and complex

Question 28

What are the products of light reactions?

Answer 28

ATP
NADPH
Oxygen

Question 29

How does metabolism work?

Answer 29

Metabolism works with energy (ATP) and reducing power (NADPH)

Question 30

What is important about rubisco?

Answer 30

Rubisco drives carbon fixation aka Calvin cycle

Most abundant protein

Question 31

What are the steps of the Calvin cycle? Is it cyclic or linear?

Answer 31

The Calvin cycle is cyclic.

It has three steps: carboxylation, reduction, and regeneration

Question 32

How is the Calvin cycle expected to function? What does it do?

Answer 32

When everything is working correctly, the Calvin cycle fixes CO2 and regenerates the precursors needed to run the cycle again.

Question 33

What two molecules should we know about the Calvin cycle?

Answer 33

Rubisco

Ribulose 1,5 -biphosphate (ruBP or rubp)

Question 34

What is rubp? What does it do in the Calvin cycle? How does it do it?

Answer 34

The CO2 acceptor molecule contains 5 carbon (C5)
Add CO2 to make a 6-carbon product
C6 product splits into two C3 products
C3 products reduced to carbohydrates
5 of the C3 products are used to regenerate rubp

Question 35

What is the net result of the carbon reactions?

Answer 35

1 Co2: 2 NADPH: 3 ATP

Question 36

How is the Calvin cycle regulated? What regulates?

Answer 36

The Calvin cycle is regulated to function in light. It is primarily regulated by the ferredoxin-thioredoxin system

(light is sensed by the thylakoid membrane activates enzymes in the chl stroma)

Question 37

Why should the Calvin cycle evolve to be regulated by light?

Answer 37

You might run out of reducing power and energy from the light reactions.
If running when there is no light (therefore no light reactions), then you might run out of the materials needed.

Question 38

What two things can Rubisco do?

Answer 38

It’s a carboxylase and oxylase
has a high affinity for Co2 but not a perfect affinity.
Can bind to both.

Question 39

What happened when rubisco meets O2 instead of Co2?

Answer 39

Calvin cycle fails to regenerate 3 ruBP.

Question 40

What is photorespiration?

Answer 40

When Rubisco binds to oxygen instead of CO2.

Question 41

What does rubisco do when it accidentally grabs O2? And what are the downsides?

Answer 41

Glycolate oxidase scavenges for carbon. It shuttles the malform product peroxisomes . Peroxisomes with mitochondria allow glycolate to be converted to glycerate, which can then be converted to 3-PGA
Photorespiration recovery requires a lot of ATP, NADPH, and ferredoxin

Question 42

What should an organism do to prevent rubisco from acting as an oxygenase?

Answer 42

Increase the concentration of CO2 through carbon-concentrating mechanisms.