WEEK 7: PHOTOSYNTESIS
PHOTOSYNTHESIS: THE BASICS:
 In photosynthesis, the
of the sun is converted into
in organic
molecules, such as sugars.
 Photosynthesis also helps remove
from the atmosphere and produce
as
a byproduct.
 CO2 enters the cell via pores in a plant’s leaves, called
.
 Plant cells contain specialized organelles called
.
PIGMENTS OF THE CHLOROPLAST:

:
Reflects green/yellow light
Absorbs blue and red light
Primary electron donor in the electron transport chain (ETC)

:
Reflects yellow light
Absorbs primarily blue light and some red light

:
Reflect orange/yellow light
Absorb blue/green light
: orange
: yellow (most abundant)
STUCTURE OF A CHLOROPLAST:
 Thylakoid Disc: A flattened membrane sac inside the chloroplast that is used to
convert
energy to
energy.
 Lumen: interior space of thylakoid discs.
 Grana: Multiple stacks of thylakoid discs. One stack of thylakoid discs is called
a
. Site of the
reactions.
 Stroma: thick fluid that surrounds grana.
PHOTOSYNTESIS:
 Photosynthesis is a “redox” reaction. Water is oxidized when it splits and CO2 is reduced
to form sugar.
Remember:
“Oxidized” means the molecule has lost electrons.
“Reduced” means the molecule has gained electrons.
 This occurs in a two-part process.
PART 1: Light
Reactions
PART 2: Light
Reactions
Also called the Calvin cycle
 Part 1
Light-Dependent Reactions
Occur in Thylakoid

Part 2
Light-Independent Reactions
Occur in Stroma
PART 1: LIGHT DEPENDENT REACTIONS:
 Occur across the thylakoid membrane.
 There are two possible routes for electron flow:
o
Photophosphorylation makes O2, ATP, and NADPH.
o
Photophosphorylation makes ATP.
 Light energy from the sun is absorbed by the chlorophyll pigments in the chloroplasts,
where it
H2O molecules by breaking the bonds between O and H.
 O2 is produced as a byproduct and the electrons are utilized in the Electron Transport
Chain.
 The Electron Transport Chain utilizes the electrons to
NADP+ to NADPH
and creates a proton gradient across the thylakoid membrane.
 The proton gradient drives ATP synthase and the phosphorylation of ADP to ATP.
WHAT IS A PHOTOSYSTEM:
 Photosystems are
complexes imbedded in the cellular membrane.
 These complexes contain
, which are used by each
Photosystem is used to reduce molecules and obtain their energy.
 Reaction Centers are accompanied by
that aid in the capture of
light.
 The captured light is absorbed and energy is transferred across the membrane in the
form of
and
.
CYCLIC PHOTOSPHORYLATION:
 Light delivers packets of energy called “
” to chlorophyll A in Photosystem
I (PS1).
 Through a “domino effect,” the electrons move through the pigments in PS1 until they
reach PS1’s
.
 The electrons are excited to a higher energy state and enter the Electron Transport
Chain.
 Hydrogen ions travel
the concentration gradient into ATP Synthase,
driving the phosphorylation of ADP into ATP.
 The electrons return to chlorophyll A in PS1, thus creating a cyclic process.
NONCYCLIC PHOTOSPHORYLATION:
 STEP 1:
.
o Light delivers photons to the Reaction Center of
where
electrons are excited to a higher energy state.
o The electrons are then passed along the
.
o As the electrons move through the Electron Transport Chain they are returned to
more stable energy states.
o Water molecules are “split” in this process, supplying electrons to PS1, and
producing
as a byproduct.
o Only small amounts of ATP are produced in this first step.

STEP 2:
.
o The electrons are then transferred to
, where more
photons are obtained from light to excite the electrons once more.
o The electrons, once again, enter the Electron Transport Chain and aid in the
reduction of NADP+ to
.
o A proton gradient is created and the flow of ______ from the stroma to the
lumen, across the thylakoid membrane, is used by ATP Synthase to
phosphorylate ADP into ATP.
o NADPH and ATP are then utilized in the Calvin Cycle.
PART 2: LIGHT-INDEPENDENT REACTIONS
THE CALVIN CYCYLE
 1 CO2 binds to 1 RuBp (5C)
 6c molecule splits into 2 molecules of 3C
 1C leaves the cycle to make glucose
 5C left replenish the RuBP
 RuBisCo is the enzyme that binds CO2 and RuBp