Lecture 14
The photosynthetic organisms capture light energy and use it to transfer hydrogen atoms from water to
acceptor molecules, in the process forming molecular oxygen, while synthesizing ATP from ADP and
phosphate. Eventually, a transfer of hydrogen atoms from acceptors to carbons from CO2 will form
glucose. Endergonic and anabolic.
Photosynthesis takes place in the chloroplast, like the mitochondria, is an endosymbiont. Inside the
chloroplast, many thylakoid exists. Pancakes stacked upon each other, filled with thylakoid lumen. The
chloroplast is like the mitochondria, with a double membrane, with the outer membrane being more
permeable.
Light reactions: 2 water + 2 NADP + 3 ADP + 3 Pi -> O2 + 2H + 2NADPH + 3 ATP
Dark reactions: CO2 + 2H + 2 NADPH + 3 ATP -> carbohydrates + water + 2 NADPH + 3 ADP + 3 Pi
An action spectrum made upon plants indicated that certain wavelengths were more preferable for
photosynthesis than others. The pigments in the thylakoid membranes are responsible for this.
Chlorophyll has 2 forms, alpha and beta, both of which has porphyrin rings, instead of using an iron, uses
a magnesium, and is very hydrophobic. Alpha has a methyl group on right upper corner, beta has an
aldehyde group on the same spot.
A photon of light strikes a molecule and pushes electrons to excited states. In photosynthesis, instead of
allowing for the electron to simply drop down into its ground state, the electron is shifted into a
neighbouring molecule. Charge separation results in the acceptor becoming negatively charged, while
the donor becomes positively charged. The acceptor is now a strong reducing agent, which is now
capable of reducing another molecule that couldn’t be reduced before. The donor will seek an electron
from another source.
A reaction centre is composed of 2 pairs of special chlorophylls, which is in the lumen of the chloroplast.
A quinone acts as the acceptor. Light harvesting complexes are composed of many different pigments,
such as chlorophyll b, carotinoids, and other pigments. These allows for a greater amount of light to be
captured to be used, and are positioned in such a way as to create a chain of resonance energy transfer.
Eventually, the energy of all these pigments are funneled into a single chlo
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