Photosynthesis

Question 1

What occurs during the light reactions?

Answer 1

• Pigment molecules capture light energy and are oxidized
• NADP+ reduced to NADPH
• Proton gradient generated, used to produce ATP

Question 2

What occurs during the dark reactions?

Answer 2

• NADPH and ATP are used to reduce CO2
• Carbon incorporated into 3C carbohydrate precursors

Question 3

The thylakoid consists of stacks of ___________.

Answer 3

grana

Question 4

Where do the light reactions occur?

Answer 4

The thylakoid membrane

Question 5

Where do the dark reactions occur?

Answer 5

The stroma

Question 6

Where is the high proton concentration during the light reactions?

Answer 6

The thylakoid lumen

Question 7

How many phospholipid bilayers are present in the chloroplast?

Answer 7

3 (outer, inner, and thylakoid membranes)

Question 8

How do chlorophyll differ from cytochromes?

Answer 8

• Instead of iron, they have magnesium
• The magnesium holds electrons instead of serving as a redox site

Question 9

Light-Harvesting Complex

Answer 9

A complex of antenna pigments.

Question 10

What happens to photon energy that doesn’t reach a reaction center?

Answer 10

It’s released as heat or fluorescence

Question 11

What happens when a chlorophyll is excited?

Answer 11

One of its electrons is promoted to a higher energy orbital.

Question 12

Is photosynthesis a cyclic process?

Answer 12

No

Question 13

What is a notable reaction at PSII?

Answer 13

Oxidation of water (to replace P680’s electron)

Question 14

What is a notable reaction at PSI?

Answer 14

Reduction of NADP+

Question 15

What molecule connects PSII and the cytochrome b6f complex?

Answer 15

Plastoquinone

Question 16

What molecule connects the cytochrome b6f complex and PSI?

Answer 16

Plastocyanin

Question 17

What is the name of the center that facilitates oxidation of water and replacement of p680’s electron?

Answer 17

The oxygen-evolving center (OEC)

Question 18

What metal does the OEC contain? What does the metal do?

Answer 18

Mn; it cycles through oxidation states as it strips protons and electrons from the waters.

Question 19

How does the OEC replace P680’s electron?

Answer 19

• It splits 2H2O into O2, 4 protons, and 4 electrons
• The Mn cycles through oxidation states as it strips protons and electrons one-at-a-time
• It gives the electrons to P680, and releases the protons into the thylakoid lumen

Question 20

What is the pathway of the excited electron from P680 to the plastoquinone pool?

Answer 20

P680 –> Pheophytin –> Plastoquinone A –> Plastoquinone B –> Plastoquinone Pool

Question 21

How many protons are translocated per electron pair that goes through the Q cycle?

Answer 21

4 protons (since the Q cycle must run twice to move 2 electrons)

Question 22

What molecule carries electrons from the cytochrome b6f complex to photosystem I?

Answer 22

Plastocyanin

Question 23

What molecule is largely responsible for generation of the proton gradient?

Answer 23

The cytochrome B6f complex

Question 24

What happens to plastocyanin’s electron?

Answer 24

It is given to P700 to replace the one that was lost when it was excited by the photon

Question 25

What is the path of the electron ejected from P700?

Answer 25

Fe-S Complex --> Ferrodoxin --> NADP+ Reductase --> NADPH

Question 26

What is notable about the structure of NADP+ reductase? What does it resemble?

Answer 26

It has an FAD group, similar to E3 on the PDH complex

Question 27

Plastocyanin is analogous to ________.

Answer 27

Complex III

Question 28

What metal does plastocyanin contain?

Answer 28

Copper (not iron)

Question 29

How does photosystem I differ from complex IV?

Answer 29

- It loses its electron via excitation - No O2, CuB, CuA

Question 30

What happens to the NADPH produced at photosystem I?

Answer 30

It goes into the light-independent reactions?

Question 31

How many protons are pumped per electron pair that passes through the system?

Answer 31

8 (4 from cytochrome b6f, 4 from the OEC)

Question 32

Where does the Calvin Cycle occur?

Answer 32

The stroma

Question 33

What reaction does rubisco catalyze?

Answer 33

It combines 3CO2 and 5RuBP to form three 6C intermediates

Question 34

What happens to the 6C intermediate produced by rubisco?

Answer 34

It splits into 2 molecules of 3PG, which then fall off rubisco one at a time (6 molecules of 3PG total)

Question 35

How is 3PG converted to BPG?

Answer 35

Phosphoglycerate kinase phosphorylates (uses ATP, 6 total)

Question 36

How is BPG converted to G3P?

Answer 36

Oxidation of NADP+ removes phosphate, generating G3P

Question 37

How many G3P go into producing carbohydrates?

Answer 37

1 of the 6

Question 38

How many G3P continue on to regenerate RuBP?

Answer 38

5 of the 6

Question 39

What are the products that can be produced through G3P and DHAP isomerization pathways?

Answer 39

- Amylose - Amylopectin - Cellulose Sugars

Question 40

What does the "sugar shuffle" do?

Answer 40

It converts 5 G3P into 3 Ru5P

Question 41

what happens to the 3 Ru5P molecules generated by the "sugar shuffle?"

Answer 41

They are phosphorylated into Ru-1,5-BP

Question 42

How many ATP are used per turn of the Calvin Cycle?

Answer 42

9 ATP (2 during BPG to G3P, 1 during G3P --> RuBP, 3 RuBP regenerated total)

Question 43

How many NADPH are used per turn of the Calvin Cycle?

Answer 43

6 NADPH (2 during BPG --> G3P, 3 molecules total)

Question 44

How often is O2 incorporated in place of CO2?

Answer 44

Approximately 20% of the time

Question 45

What is the byproduct produced by photorespiration?

Answer 45

2-phosphoglycolate

Question 46

What is the cost of photorespiration?

Answer 46

ATP, NADH, & time