Biology 1002B Lecture Notes - Lecture 6: Lincomycin, Thylakoid, P680
4 views8 pages
Lecture 6 Photosynthesis 01/22/16 Anuj Gupta
definition of photosynthesis, oxidation, reduction, oxidation-reduction reaction, light
reactions, Calvin cycle, redox potential, chloroplast, thylakoid membrane, lumen, P680,
P700 (+ and * for each), chemiosmosis
oAka carbon fixation or primary productivity
oTake atmospheric CO2 or CO2(aq) from such an environment and use the energy
of light to drive the formation of CO2 into sugar.
oEndergonic Process. The G in 1 glucose molecule is higher than 6 molecules of
oAlso an anabolic process, and an oxidation-reduction reaction.
oThere is no usable energy in CO2. This is because there are no readily accessible
or usable electrons. It’s a fully oxidized form of C. But there’s lots of usable
energy (because of lots accessible electrons). We know this because there are lots
of C-H bonds. Molecules that have lots of G have lots of C-H bonds (e.g fat,
The reason C-H bonds
have lots of E is because
neither the C nor the H are
very electronegative (do
not have a strong
attraction for the electrons
that make the covalent
bond). Therefore it is
easier to oxidize those
molecules or steal their
oWater is oxidized into oxygen
oOxidizing agent Something that oxidizing something else (i.e. it itself is
oCO2 is reduced into sugar
oReducing agent Something that
reduces something else (i.ie it
itself is oxidized)
Oxidation-Reduction Reaction (aka
oFixing CO2 into glucose, using the
electrons from H2O.
oE.g. photosynthesis. Note that the oxidation of water and reduction of CO2 do not
occur near each other.
oProduce ATP. Free energy from sunlight is used to drive the conversion of ADP
and inorganic phosphate into ATP. Also NADPH is made as well. ADP and
NADPH are reduced in this endergonic process. NADPH is source of reductant
(acts as reducing agent, provides H+ and electrons) whereas ATP provides energy.
oOccurs on the thylakoid membrane
oOccurs in the stroma
oSomething that is a strong reducing agent (it can give up its electrons easily) has a
more negative or lower redox potential.
oSomething that is a strong oxidizing agent (it strongly wants electrons) has a
higher + redox potential.
oOrganelle in plants where photosynthesis occurs. Contains its own nuclear
oMembrane surrounding the thylakoid, containing in the lumen. On the membrane
itself is the location of the light reactions.
oFluid contained within the thylakoid membrane.
P680 (unexcited, in PS
is fully oxidized
and has to the
ability to take an
water. P680+ is
oxidant (it can
pull it from
This is why Chlamy can be negative phototactic. The photosynthetic
apparatus can absorb too much light (only can handle ~10000
photons/second). PS II is constantly being damaged and repaired and
this process cannot be stopped.
D1 holds P680+ together. D1 gets damaged often so the PS needs to be
disassembled and a new D1 is put in and then reassembly occurs.
D1 is one of the few proteins coded by the chloroplast genome.
oP680* Chlorophyll in the excited state, waiting to be used in PS II.
oA chemical gradient formed by a higher concentration of protons in one area than
another. In the light reactions, the high concentration is found in the lumen and is
formed by the splitting of water and the ETC. Used to do work as protons diffuse
via active transport through ATP Synthase which uses its energy to make ATP
Structure of chloroplast (use your model of Chlamydomonas and link that to structures
and compartments seen in Figure 7.3)
Left Side: Shows abundance of D1 protein in Chlamy cells that were
exposed to normal low light. Lincomycin is an antibiotic that
inhibits chloroplast protein synthesis (stops translation in
chloroplast). Top shows that the rate of damage of D1 is equal to
the rate of repair. Bottom shows that blocking the synthesis of D1
protein causes the rate of damage > rate of repair decreasing
abundance of D1.
Right side: In really high light, D1 protein abundance drops. In the
flask with Lincomycin the drop is much steeper. Additionally, the D1
abundance of it barely changes. In the control, there is a nice
rebound of control so it recovers nicely in low light.