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Lecture 1

BIOL 1201 Lecture Notes - Lecture 1: Primase, Ribosome, Ribose


Department
Biological Sciences
Course Code
BIOL 1201
Professor
E.Wischusen
Lecture
1

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BIO 1201
Photosynthesis
Photosynthesis:
Doesn’t occur in all organisms but it impacts all organisms at some
point.
Equation: 6CO2+12H2O+Light 6CO2+C6H12O6+6H2O
Convert two low energy molecules into a high energy molecule
Reactions are largely endergonic; light is the required energy
Note: You start with different water molecules than what water is
produced in the end.
Two Stage Process:
1. Capture the light energy in chemical energy (light reactions)
2. Use the chemical energy to convert CO2 into glucose (Dark Reactions
or Calvin cycle)
a. Linked together by ATP and NADPH+
Chloroplast Structure:
Has two transparent outer membranes
Individual thylakoid membranes discs of membranes
o Green pigments are found in the thylakoids
Granum is a stack of thylakoids
Stroma is the liquid portion of the chloroplast
Calvin Cycle
Calvin Cycle (Dark Reaction):
Occurs in the stroma
Inputs and outputs of this cycle?
o Inputs: carbon dioxide (joins to intermediate into cycle), ATP
and NADPH + H+
o Outputs: G3P Glyceraldehyde 3-phosphate, ADP, and NADP+
Where do we get the energy for the Calvin Cycle?
Energy to drive dark reactions from energy of light reactions
o Light reactions come in two forms:
Cyclic and Non-Cyclic Phosphorylation
Add phosphate to an ADP to make ATP
Photophosphorylation
Photophosphorylation (light reactions):
Using light to add a phosphate to ADP
The function of the light reactions is to capture light energy and
convert it into chemical energy in the form of ATP and NADPH + H+, which
the Calvin cycle later uses to convert CO2 into a sugar (G3P).
Photosystem: a collection of hundreds of pigment molecules with proteins
imbedded in the thylakoid membrane.
Photosystems I (right) and II (left)
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o Antenna Pigments:
~200 molecules of Chlorophyll a
~50 molecules of Chlorophyll b
~50 other pigments
o Reaction Center Molecules
Reaction center molecules are special versions of
Chlorophyll a (P700 or P680) are imbedded in the
thylakoid membrane, which holds the light energy given
off by the pigment molecules.
How a photosystem harvests light?
1. Light hits the pigment molecules that absorb energy, and the
energy gets passed from pigment molecule to pigment molecule
(transfer of energy).
2. This process happens until that energy gets to reaction center.
3. When the energy gets to the RCM, that energy can be used to
energize electrons and create a pair of high-energy electrons.
4. A primary electron acceptor accepts those electrons.
o This step is where the photosystem actually captures the
light energy.
Photosystem Structure:
Photosystem 2 on the left and photosystem 1 on the right with a
series of proteins that can accept/give up electrons (cytochrome
chain).
Why have so many types of pigments in a photosystem?
Each different pigment molecule absorbs different wavelengths of
light, so it can absorb a broader spectrum of light energy.
o As a result, the plant can use a wider range of light it is
receiving.
Non-Cyclic Electron Flow (photophosphorylation):
Flow from one photosystem 2 to photosystem 1
Electrons will flow through rather than cycle in the system.
Overview of process:
o H20 Photosystem 2 Cytochrome complex Photosystem 1
NADPH Calvin Cycle
Inputs and Outputs:
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o Inputs:
Light, H2O, ADP, NADP+
o Outputs:
O2, ATP, NADPH+H+
Non-Cyclic Photophosphorylation Process:
1. Light strikes photosystem 2, and the energized electrons (from
water) produced from the P680 RCM are then passed through the
cytochrome complex.
a. Water is the source of electrons. Water is split into ½ O2, 2
electrons, and hydrogen ions. All of which will be later
used in the system.
2. At one point on this chain, hydrogen ions are pumped from one
side of the chain to the other (creates a hydrogen ion gradient).
The hydrogen flows through an ATP synthase to produce the ATP.
3. Electrons continue to flow until the P700 RCM on photosystem 1
where light energy is transferred form pigment molecule to
pigment molecule. This transfer of energy energizes those
electrons, which are then picked up from another primary electron
acceptor.
4. Passed on to another electron acceptor, and ultimately, those
electrons are used to reduce NADP+ into NADPH (later used in
Calvin Cycle).
Cyclic Electron Flow:
Overview of process:
o Photosystem 1 Cytochrome Complex Photosystem 1
Inputs and Outputs:
o Inputs:
Light, ADP
o Outputs:
ATP
Cyclic Photophosphorylation Process:
1. After the electrons are energized in photosystem 1, the electrons
then flow down the cytochrome chain back to photosystem 1.
2. The hydrogen ions flow across the membrane through ATP synthases to
make ATP.
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