Lecture 1: Intro and Chlamydomonas
1. Roles of light as used by life
Photosynthesis and carbon fixation
2. Characteristics of Chlamydomonas that make it a useful model system
a sexually active, light harvesting, carbon-reducing, hydrogen belching planimal
function of basic components of Chlamydomonas cells
Large central nucleus
2 basal bodies
Flagella develop from this organelle
Center of carbon fixation Co2 --> organic
Harvests light (not to do is photosynthesis)
Chlamydomonas are extremophiles
relative usefulness of various biological characteristics as measures of complexity
How large a organism is
o C value paradox
o PCG - protein coding genes
Rise of multicellularity and eukaryote
advantages to Chlamydomonas in being phototactic.
Respond to fluctuating light levels which is there primary source of energy
reasons why Chlamydomonas might move AWAY from a light source.
Wrong colour, too much energy
Destroy photosynthetic apparatus
basic structure of rods and cones as photoreceptor cells.
Rods --> black/white
Cones --> colour
Rods and cones are photoreceptor cells
o Sit on retina
Located in discs which are in the eye major components involved in phototransduction and their role.
o One photon changes from cis-retinal to trans-retinal
Transducin activates a phosphodiesterase
which breaks a bond in cyclic GMP
Lecture 2: Light - Energy and Information
1. Relationship between excited states of a pigment and its absorption, fluorescence
2. Region of the electromagnetic spectrum known as “visible light”.
Wavelength of 400nm (violet, more energy) to 700nm (red, less energy).
Ultraviolet comes before, infrared comes after
Relationship between wavelength and energy content of a photon.
Molecular characteristic of visible pigments that make them able to absorb light.
Pigments absorb light (ex. Chlorophyll)
Non bonding / pi orbital electrons can trap light
Conjugated ring system = absorb light?
Relationship between pigments and associated protein.
Pigments are bound to proteins non-covalently
o This produces pigments-protein complexes
Gel electrophoresis resolves pigment-protein complexes
Four “fates” of the excited state of chlorophyll resulting from absorption of
Decay, Heat, Fluorescence, Photochemistry and Energy Transfer
Reason(s) why relative fluorescence is different in isolated chlorophyll vs. intact
cells when exposed to light.
What accounts for the fact that chlorophyll is green in colour
Chlorophyll is green because there is no excited state that absorbs green Quantitative relationship between photons and excited electrons.
Relationship between energy of photon and energy required to excite electrons in
order for photons to be absorbed.
General structure of photosystem.
Antenna outside, reaction center in middle
Energy transfer occurs in antenna
Similarities and differences of the light capturing and photochemistry of
phototransduction (retinal) vs. photosynthesis (chlorophyll).
Photochemistry takes place at photoreceptor
o Isomerization of retinal
How are excited states of antennae pigments organized to provide for energy
transfer to reaction center.
Reaction (antenna): Chl+ + Chl --> Chl + Chl+
o Not oxidation/reduction reaction
o Not photochemistry
Reaction in reaction center: Chl+ --> Chl+ + e-
o Used for electron transport
Structure of rhodopsin.
Rhodopsin = retinal + opsin:
o Retinal = pigment, opsin = protein
o Double bond prevents rotation (Cis/Trans)
Effect of photon absorption by 11-cis retinal on retinal structure followed by
association with opsin protein followed by interaction of transducin with opsin.
11 cis (dark) changes to all trans retinal when light hits it
This is called photo-isomerization (double bond breaks and then reforms)
This process is spontaneous, very rare to occur without light
Transducin can only gain access to the rodopsin when trans is active, in cis the binding site
is not accessible
Reasons why life has evolved to detect the narrow band of energy represented by
Everything in bio that uses light uses visible light
Visible light is the most dominant form of EM radiation
Energy in visible light is perfect for exciting electrons
o Enough energy to drive photochemistry Lecture 3: Protein Structure and Function
1. reasons why photosystems have antenna proteins while the eye doesn’t.
2. points of control for regulation of protein abundance.