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Lecture 3

BIOL 1201 Lecture Notes - Lecture 3: Photosystem Ii, Thylakoid, Photosystem I

Biological Sciences
Course Code
BIOL 1201
Bill Wischusen

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Biology Exam 3 Notes
Does not occur in all organisms, but impacts all organisms in one way or another
6CO2+12 H2O + Light 6 O2 + C6H12O6 + 6H2O
o Pretty much the opposite of cellular respiration
o Convert 2 low energy molecules into a high energy molecule using the
energy from light
o Endergonic reaction requires energy to start reaction
o Water molecules on both sides of the equation
From a chemistry standpoint, could cancel out the water on both
But technically the water on each side is different water molecules
(one is put in and one is water that is produced)
Concerned with the fate of oxygen in water (in the reactant side)
Where does the oxygen for glucose and water come from?
What is the fate of the oxygen in water (reactant side)?
o Oxygen in the reactant side water molecule gets released as oxygen
o Plant needs electrons water as a source of electrons
To get that, it will create electrons, protons, and waste product of
oxygen that we breathe out
Two Stage Process
o 1st Phase: Light Reactions
Capture light energy in form of chemical energy
o 2nd Phase: Dark Reactions/ Calvin Cycle
Use chemical energy to convert CO2 into glucose
Don’t directly require light
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o Overview Form:
In light reactions, producing high energy molecules ATP and
Energy to make these molecules make from the light
These high energy molecules are now used to convert CO2 into a
Output of Calvin Cycle are some low energy intermediates or low
energy versions of those molecules (ADP and NADP+)
These molecules will be reenergized
Reduce NADP+
Phosphorylate ADP
All of this occurs in a chloroplast
Which of the following best describes the light reactions?
o Capture light energy and convert into chemical energy
*We do not know how to convert energy into matter
We do know how to capture energy and convert it to another type of
Where do the dark reactions occur?
o Calvin Cycle is the dark reactions
o They occur in the stroma (inside chloroplast but outside thylakoid)
o Light reactions are happening in or on thylakoid membranes
Photosynthetic Structures
o 2 outer membranes that surround it
o 3rd set of membranes inside it (thylakoid membranes)
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Surround the disk structures
Stack of thylakoids is called the granum
o The liquid portion of the chloroplast outside of the thylakoids is the stroma
o All reactions for photosynthesis occur inside chloroplast
Stroma: dark reactions
Thylakoid: light reactions
o The only actual green stuff is in the thylakoid membranes
Calvin Cycle
One of the 2 stages for photosynthesis
o Second stage: Dark Reactions or Calvin Cycle
o Occurs in the stroma
o Endergonic process gets energy from the light reactions
o CO2 joining to intermediate already in cycle
CO2 is 1 Carbon molecule
Intermediate is a 5 carbon molecule
So it makes a 6 carbon molecule
Then the 6 carbon molecule breaks down into two 3-carbon
In the process of breaking down the 6 carbon molecule, you will
convert ATP to ADP to so you are going to add energy into the 3-
carbon molecules
Will also do a redox reaction where NADPH+H+ is converted into
Oxidizing the NADPH+H+
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