Biology 1002B Lecture Notes - Lecture 8: P680, Starch, Photosystem

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18 Apr 2012
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Photosynthesis (7-7.3)
Photosynthetic organisms are photoautotrophs and are classified as the primary producers of
the earth
Photosynthesis is the major biological process that allows for energy to enter biosphere
(important)
Chlorophyll is abundance in aquatic and land environments
o Aquatic environments that are very cold are photosynthetic hotspots, not those that are
hot
Two parts of photosynthesis: Light dependent reaction and light independent reaction (Calvin
cycle)
Transforming light energy into chemical energy (sugar)
Takes place in chloroplasts
Definition: The light dependent conversion of CO2
(inorganic carbon) into an organic form
Carbon Dioxide vs. Sugar
Metabolic process
Light dependent conversion of CO2 (inorganic) into
organic form
No useable energy in CO2
o Can get electrons away from molecule oxygen
too electronegative
Sugar
o Lots of usable energy
o Calories
o C-H bonds not electronegative, easier to pull electrons away and therefore work can
be done
Photosynthesis is an endergonic reaction as potential energy goes up. Energy comes from light
Redox Process
Photosynthesis is a redox reaction in which water is oxidized, carbon dioxide is reduced
o The Light Reactions
Occurs in grana
Split water
Release oxygen
Produce ATP
Form NADPH
Powered by energy of the
sun
o Calvin Cycle
Occurs in stroma
Forms sugar from CO2
Use ATP for energy and
NADPH (electron source)
for reducing power from
light reactions
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Energy & Information
Light Photosynthesis Energy Source
Light Vision Information
Chlamydomonas Reinhardtii uses light for both info and energy
o Photoplankton (algae)
o Eyespot
Phototaxis ability to move in response to light
based on amount of light needed (ie, closer or farther)
Light
Key concept
o Light reactions convert solar energy
to chemical energy (ATP, NADPH)
Light
o Form of electromagnetic energy
which travels in waves
o Also behaves as particles of light
(photons)
o Wavelength
Is the distance between the crests of
waves
Determines the type of
electromagnetic energy
Inversely related to energy
E = hc/λ
o H=planck’s constant, c
is speed of light, λ is wavelength
o Photons must be absorbed
Pigments
o Substances that absorb visible light (photons) (light receptors)
o Chlorophyll a & b and carotenoids major photosynthetic pigments in plants, algae, etc
o All have conjugated double bonds
Double bonds separated by one carbon-carbon single bond Alternating double
bonds
Way to represent electrons that are not involved in bonding
π orbital electrons
Can be used for light absorption
o Bound to proteins (cofactor like)
Chromophore (pigment attached to protein)
Light Absorbed
Process
o Single molecule of chlorophyll
o Expose chlorophyll to white light (full visible
spectrum)
Specifically red, green and blue light
o Chlorophyll can absorb blue light (high energy)
o Energy transferred to electron from ground state
to higher excited state
One photon excites one electron
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