Non – Cyclic Electron Transport

•non-cyclic the electrons do not return to the source

•non-cyclic process occurs to produce ATP AND NADH which will be used by the Calvin cycle to produce the carbohydrate but some times there occurs a cyclic process to produce ATP to cope up with Calvin cycle as it requires more ATP than the NADH

•the electrons come back to the source

•cyclic electron flow could operate independent of photosystem II

Non – Cyclic Electron Transport

Cyclic Electron Transport

Non-cyclic Electron

Transport in Photosynthesis

DIFFICULT words and

terms..!

...Be AWARE!

Photophosphorylation

refers to the use of light energy from photosynthesis to ultimately provide the energy to convert ADP to ATP, thus replenishing the universal energy currency in living things.

Photosystem I• the light energy complex for the cyclic electron transport process used in some photosynthetic prokaryotes.

• makes use of an antenna complex to collect light energy for the second stage of non-cyclic electron transport. It collects energetic electrons from the first stage process which is powered through Photosystem II and uses the light energy to further boost the energy of the electrons toward accomplishing the final goal of providing energy in the form of reduced coenzymes to the Calvin cycle.

Photosystem II

• makes use of an antenna complex to collect light energy for the first stages of non-cyclic electron transport

• contains the same kind of chlorophyll a as Photosystem I but in a different protein environment

present in every living cell is NAD+. It participates in electron transport reactions in cell metabolism processes like glycolysis

Coenzymes

Pheophytin

is a chemical compound that serves as the first electron carrier

intermediate in the electron transfer pathway of photosystem

II

Plastocyanin

an important copper-containing protein involved in electron-

transfer

thylakoid •a membrane-bound

compartment inside chloroplasts and cyanobacteria

•the site of the light-dependent reactions of photosynthesis

•consist of a thylakoid membrane surrounding a

thylakoid lumen

Plastoquinone (PQ)

•a molecule involved in the electron transport chain in the light-dependent reactions of

photosynthesis.

•Plastoquinone is reduced (accepts two protons (H+) from the stromal matrix of the chloroplast, coupled to two electrons (e-) from photosystem

II), forming plastoquinol.

•transports the protons to the lumen of thylakoid discs, while the electrons continue through the

electron transport chain into the cytochrome b6f protein complex

Ferredoxins

are iron-sulfur proteins that mediate electron transfer in a range of

metabolic reactions

Nicotinamide adenine dinucleotide phosphate (NADP)

a coenzyme used in anabolic reactions, such as lipid and nucleic

acid synthesis, which require NADPH as a reducing agent.

Adenosine (ATP)

•a multifunctional nucleotide used in cells as a coenzyme

•transports chemical energy within cells for metabolism

noncyclic photophosphorylation

•a two-stage process involving two different chlorophyll photosystems

•occurs on thylakoid membranes inside chloroplasts

noncyclic photophosphorylation

•water molecule is broken down into 2H+ + 1/2 O2 + 2e- by a process called photolysis

two electrons from the water molecule are kept in photosystem II, while the 2H+ and 1/2O2 are left out

for further use

a photon is absorbed by chlorophyll pigments on the surrounding of the reaction core center of the photosystem. The light excites the electrons of each pigment, causing a chain reaction that eventually transfers energy to the core of photosystem II , exciting the two electrons that are transferred to the primary electron acceptor, pheophytin

The deficit of electrons is replenished by taking electrons from another molecule of water. The electrons transfer from pheophytin to plastoquinone, then to plastocyanin, providing the energy for hydrogen ions (H+) to be pumped into the thylakoid space. This creates a gradient, making H+ ions flow back into the stroma of the chloroplast, providing the energy for the regeneration of ATP.

The photosystem II complex replaced its lost electrons from an external source; however, the two other electrons are not returned to photosystem II as they would in the analogous cyclic pathway. Instead, the still-excited electrons are transferred to a photosystem I complex, which boosts their energy level to a higher level using a second solar photon.

The highly excited electrons are transferred to the acceptor molecule,

but this time is passed on to an enzyme called Ferredoxin- NADP + reductase,

for short FNR, which uses them to catalyse the reaction (as shown):

NADP+ + 2H+ + 2e- → NADPH + H+

The concentration of NADPH in the chloroplast may help regulate which pathway electrons take through the light reactions. When the chloroplast runs low on ATP for the Calvin cycle, NADPH will accumulate and the plant may shift from noncyclic to cyclic electron flow.

Thank you for

listening

GROUP 9

MILTEOFE S. DAYANDAYAN

CHEDIROSE SALAZAR

MICHAEL ANDREW YGNACIO

FERNANDO SARDIDO