Photosynthesis: Photosystem Overview

Study Notes

Photosystems are aggregates of pigments and proteins in the thylakoid membrane
They are responsible for absorbing photons (packets of light energy) and transferring the energy
They are composed of light-harvesting complex and reaction-center complex

Discovered after Photosystem I
Functions first in the light reaction of photosynthesis
Its chlorophyll a in the reaction center absorbs light with a wavelength of 680nm
Light energy is trapped and boosts electrons to a higher level
Electrons are received by an electron acceptor
Electrons are passed from one acceptor (plastoquinone and cytochrome) to the next photosystem
Energy lost reduces the electron
The diagram indicates the process with the reactants and products involved like water, oxygen, and protons
This photosystem is on the thylakoid membrane
Occurs in the thylakoid lumen

Discovered first
Its reaction-center has a chlorophyll a called P700
Effective in absorbing light with a wavelength of 700nm
Electrons from photosystem II lose energy when they pump H+ across the membrane
Light gives electrons energy to combine with protons from split water to reduce NADP+
Electrons go through the electron transport chain (ETC) to produce NADPH
Located on the thylakoid membrane
NADPH is used in the next set of reactions

Antenna complex
Consists of several different pigments (Chlorophyll a, chlorophyll b, carotenoids) bounded with proteins
When a pigment molecule absorbs a photon, energy is passed on from one pigment molecule to another until the energy reaches the reaction center

Composed of a pair of chlorophyll a and a primary electron acceptor
The primary electron acceptor is a specialized molecule that can accept electrons from chlorophyll a
The pair of chlorophyll a in the reaction center is specialized because they are capable of transferring an electron to the primary electron acceptor and not just boosting the electron
Located in the thylakoid membrane