29. Light rxns

Reactaants of photosynthesis

6CO2 + 6H2O

Product of photosynthesis

C6H12O6 + 6O2

Primary energy source of photoynthesis

sunlight to convert CO2 to sugar

What is the starting electron donor in mitochondria ETC?

NADH (and FADH₂)

What is the starting electron donor in chloroplasts ETC?

H₂O, which is split by PSII to supply low‑energy electrons.

What is the first major complex in chloroplast ETC?

hotosystem II (PSII), which splits water and energizes electrons with light. P680

P680

PSII reaction center that becomes a strong oxidant and pulls electrons from water.

Why do chloroplasts need light to start electron flow?

H₂O electrons are low‑energy and must be energized by P680 in PSII using photons.

What is the final electron acceptor in mitochondria?

O₂, which becomes H₂O at Complex IV.

What is the final electron acceptor in chloroplasts?

NADP⁺, which becomes NADPH after PSI.

What is the energy direction of electron flow in chloroplasts?

lectrons move uphill, requiring light energy from PSII and PSI.

Where is the proton gradient formed in chloroplasts?

Across the thylakoid membrane, into the thylakoid lumen.

What ATP synthase is used in mitochondria?

F₁F₀ ATP synthase, with protons flowing into the matrix.

ATP synthase in chloroplast

CF₁CF₀ ATP synthase, with protons flowing into the stroma

What are the main products of chloroplast ETC?

ATP + NADPH for the Calvin cycle.

Light is converted to chemical energy

in the form of

ATP and NADPH.

Where in the chloroplast is [H+] high

in the thylakoid lumen.
pH4

Where in the chloroplast is [H+] low

in the stroma.

pH8

In mitchondria, what is the most important gradient for energy

electrical gradient

In chloroplasts, what is the most important gradient for energy

chemical gradient is

the more important

source of energy

Light harvesting complex embedded in thylacoid membrane

surround the reaction center and funnel energy to

the reaction center.

primary light acceptor in most photosynthetic systems

chlorophyll

Carotenoid (acessory pigment) turns into

vitamin A- required for human vision

Memory trick for major photosynthetic pigments

ROYGBIV

Which pigment has highest nergy

violet

Which pigment has lowest energy

red

Photosynthesis begins with the absorption of

light by

photoreceptor molecules/pigments

(e.g., chlorophylls and carotenoids)

Resonance energy transfer

is the process by which energy absorbed by a pigment is transferred to another pigment molecule, enhancing the efficiency of light absorption during photosynthesis.

During resonance energy trasnfer, youcan only transfer from a donor to

acceptor of equal or lower energy

Antenna pigments

harvest light energy

and transfer it to reaction centers in

photosystem II and I

Photosystem II contains

special-pair chlorophyll molecules (P680) that undergo charge separation and donate e- to the photosynthetic ETC

Photoinduced charge separation

converting light energy into reducing power (electron acceptor is now negatively charged A-)

Charge separation occurs between

a special pair, at a site called the reaction center.

Z-Scheme

An arrangement of electron carriers from Photosystem II to I

PSII reduction potential

is low

PSI reduction potential

is higher than PSII's, facilitating electron transfer to NADP+.

What moves electrons from PSII to PSI

Q and cytochrom bf complex

Special pair chlorophyll

in P680 (PS II) is excited

by a photon and becomes

P680*

P680*

transfers energy

as an e- to pheophytin

A through a charge

separation step.

oxidized P680+

is re-reduced by e- derived from the

oxidation of water to P680

Mn center aka WOC

in Photosystem II is where H2O splitting occurs to get electrons

What 2 things are reuired for H20 splitting in PSII

Mn and Ca

During H20 splitting what happens to Mn

goes through 2+, 3+, 4+, 5+

During H20 splitting what happens to Ca

stays 2+

O2 production during photosynthesis evolved around

3.5 billion years ago

Electrons from PSII move through

PQ (plastiquinone) and plastocyanin to PSI

Photosystem I

transfers electrons through an

iron-sulfur complex to reduce ferredoxin, …… which then

reduces NADP+ to generate NADPH

Why is hydrolysis used instead of condensation?

light reactions need electrons, and hydrolysis splits water to supply them.

What if NADP+ is not available as terminal electron acceptor ????

cyclic electron flow can still make

a H+ gradient to power ATP production

Why can plants still make ATP without NADP+

protect chloroplasts and plants under some stress conditions

Paraquat

toxic herbicide that blocks photosynthetic ETC

Paraquat in humans

produces

Superoxide radicals that

react with unsaturated

membrane lipids……

die from organ failure……..

Paraquat derivative

Atrazine

Green chlorophyll in potatoes suggests

presence

of solanine (a toxic alkaloid)

solanine

nhibits acetylcholinesterase – an enzyme

crucial for controlling the transmission of nerve

impulses