LECTURE 11

Question 1

In photosynthesis, e- from the H atoms in H2O are

Answer 1

Transferred to CO2, reducing it to carbohydrate

Question 2

When light hits, 3 things can occur

Answer 2

1) light is reduced
2) light is transmitted (goes through)
3) light is absorbed (disappears)

Question 3

Pigments

Answer 3

Substances that absorb light

Question 4

Chlorophyll a

Answer 4

The main photosynthetic pigment

Question 5

Accessory pigments

Answer 5

1) . Chlorophyll b

2) . Carotenoids

Question 6

Chlorophyll b

Answer 6

Broadens spectrum used for photosynthesis

Question 7

Carotenoids

Answer 7

Absorbs excessive light that may damage chlorophyll

dissipates E in the form of heat

Question 8

What happens when a pigment molecule absorbs a photon ?

Answer 8

Photon absorbed by pigment, e- raised form ground state.

There are two possibilities from here:
1) returns to ground stage and gives off heat

2) returns to ground state and gives off
- photon < E (longer wavelength)
- heat

Question 9

How does absorbing a photon of a specific wavelength giving off a slightly larger wavelength allow the plant to use the photons as E?

Answer 9

In a plant chloroplast, the chlorophyll a molecules are assembled with other components of the thylakoid membrane.

• this allows the E of the photons to be absorbed for a useful purpose.

Question 10

What are all the parts of a light reactions

Answer 10

1) light reaction
2) pigment
3) structures involved in photosynthetic electron transfer

Question 11

Structures involves in photosynthetic electron transfer

Answer 11

Located in the thylakoid. Many small molecules and large enzyme complexes are involved :

• PS ll
• water splitting enzyme
• cytochrome b6f complex
• PS l
• SADP reductase

Question 12

PS l and PS ll

Answer 12

The photosystems consist of a reaction center complex surrounded by light harvesting complexes

Question 13

Reaction center

Answer 13

E form absorbing of photons in all other pigment molecules in the photo system is transferred to a pair of chlorophyll a molecules in a reaction center

Question 14

What do the special pair of chlorophyll a molecules in the rxn Center do?

Answer 14

They absorb a specific wavelength of light

Question 15

The light harvesting complexes

Answer 15

Transmit E via resonance E transfer

Question 16

Reasonance E transfer

Answer 16

Involves the transfer of E. Required the molecule to be very close to each other

Question 17

When the special pair of chlorophyll a molecules receive E, they

Answer 17

Donate an e- to the primary e- acceptor (pheophytin), the special pair is now photooxidized because oxidation was caused by light.

Question 18

What is the primary e- accceptor

Answer 18

Pheophytin

Question 19

Where does the reaction on PH ll happen

Answer 19

In the stoma

Question 20

First three steps to PS ll and l

Answer 20

1) photon strikes a pigment modules in PS ll
2) e- is transferred to primary e- acceptor (pheophytin). Loss of e- leaves holes that must be filled.
3) H2) is plot and its e- are transferred one at a time to P680+ (reducing it to P680). The 2 P+ are released into the thylakoid space.

Question 21

P680 +

Answer 21

Very strong oxidant agent

Question 22

How many e- required to split H2O

Answer 22

2

Question 23

Where are protons stored

Answer 23

Thylakoid

Question 24

What causes “e- holes”

Answer 24

The ejection of e- (using E form light) leaves holes in reaction center chlorophyll a molecules

Question 25

What are steps 4 and 5 of the light PS ll and l

Answer 25

4) photo excited e- mov3e to PS l via e- transport chain

5) e- “fall” to a lower E level (exogeronic)
Proton pumping driven by e- moving through cytochrome b6f complex (4H+ enter per H2O lysed)

Question 26

What is the primary e- acceptor for PS l

Answer 26

It’s unknown

Question 27

What do light harvesting PS l pigments cause P700 to do

Answer 27

They lose e-, to becomes P700+

Question 28

What does the proton gradient in steps 4 and 5 form?

Answer 28

The thylakoid space

Question 29

Summary of linear e- flow down e- transport chain

Answer 29

Primary e- acceptor (pheophytin)

Plastoquinone (Pq)

Cytochrome b6f complex

Plastocyanin (Pc)

• (Potential E decreases with each transfer)
• at PS l, the e- replace those lost form PS l as it harvest light E.

Question 30

Steps 6,7,8 of PS ll and l

Answer 30

6) light harvesting PS 1 pigments independently cause P700 to lose e- (becoming photooxidized P700+)
7) P700+ accepted e- that arrive via the e- transport chain of PS ll

8) NADP+ reductase catalyzes the transfer of e- form freedom in (fd) to NADP+, 2e- and 1H+ (from stroma) are required to make NADPH.
NADPH caries on to the Calvin cycle.

Question 31

Non-cyclic photorylation

Answer 31

Formation of ATP via the process of linear electron flow pathway.

(H2O one one end, NADP on the other)

Question 32

What is the source of electrons in the linear electron flow patheway ?

Answer 32

H2O since its continuously replacing those lost from chlorophyll a reaction center molecules

Question 33

Within the thylakoid space,

Answer 33

High conc. Of P+ (H+) boules up (high potential E)

Question 34

Chemiosmotic coupling

Answer 34

Explains how ATP can be made from a P+ conc. Gradient across a membrane

Question 35

How discovered chemiosmotic coupling

Answer 35

Peter Mitchell

Question 36

The linear e- flow pathway creates

Answer 36

ATP and NADP simultaneously (required light and the lysis of H2O)

Question 37

The carbon fixation rxn requires

Answer 37

1.5 X more ATP then NADPH

Question 38

How can the cell produce ATP with out marketing excess NADPH?

Answer 38

Plants use PS l plus some of the e- transfer system to make only ATP.

• plants sense levels of NADPH, depending on the balance of ATP : NADPH, that can negate in Schlick electron flow pathway.

Question 39

Cyclic electron flow

Answer 39

• no production of NADPH
• no release of oxygen
• but it can make ATP form P+
  (2H+ transferred from stroma into thylakoid space per e-)

Question 40

Plants have a defective cyclic pathway that can only grow in

Answer 40

Low light levels; might protect plants form high intensity light

Question 41

What PS system does cyclic electron flow use?

Answer 41

PS l, NOT PS ll

Question 42

Summary of cyclic e- flow

Answer 42

1) e- end up back to full “holes” in the PS l rxn Center
2) the transfer of e- is from ferredacin to plastoqiunone, instead of the NADP+
3) P+ pumping of cytb6f complex from stroma to thylakoid space creates a H+ gradient.
4) in this manner, ATP is produced via: cyclic photophosphorylation