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Bio First Midterm Notes

Course Code
BIOL 1002B
Tom Haffie
Study Guide

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Bio 1200b First Exam Review
Will Burke
Lecture 1 - Chlamydomonas
How does light interact with biology? Two major ways A source of ENERGY and a source of
INFORMATION. Chlamydomonas is a perfect example. Chlamy contains an eyespot within its chloroplast.
It is used to enable the cell to orientate itself with light so it can harvest lots of it. It will swim towards
the light source to maximize photosynthesis.
Chlamydomonas are very popular in labs and can grow in all different conditions from warm to the
Antarctic. These are called extremophiles. They would die under standard conditions.
Almost all eukaryotic cells are much larger than a bacterium. Chlamy has a thousand times larger
volume than E.Coli. Complexity can be defined as genome size, though this is inaccurate in many cases
as similar organisms have drastically different genome sizes. It is not so much about genome size but
Phototaxis - Movement towards light. Chlamy also runs away from light when there is too much light.
Too much light the cells damage when they harvest too much because it produces reactive oxygen that
kills the cell.
The eyespot and the eye appear to be homologies.

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Lecture 2 - Light
Light behaves like a wave. The shorter the wave length (gamma rays) the higher the intensity. Light can
also be seen as small packets (photons). The amount of energy can be compared (energy in red light vs.
green light). The energy in a blue photon is the highest (shortest wavelength).
Molecules that absorb light are called pigments (absorb photons). Example Chlorophyll, Indigo.
Pigments contain alternating double and single bonds and thus many non-bonding electrons. These are
what interact with the photons of light (not required to bond, can trap energy). Exception Retinal
involves bonding electrons.
Pigments are bound very specifically to proteins. When you isolate the protein you can keep the
pigment attached and the protein has color (pigment-protein complxes). The pigment is bound non-
covalently to the protein (care is required to keep the pigment attached because these bonds are weak).
Protein electrophoresis Mitochondrial proteins run on a gel do not have color so a stain is required to
detect them. With pigment-protein complexes there is no need for a stain as the pigment displays color.
TAKE HOME Pigments are not free, they are bound.
Light Absorption An electron can exist in a ground state or an excited state. In chlorophyll there are
two excited states. If white light is shone on the electron it will be transferred to the higher excited state
(blue photon) or the lower excited state (red photon). If it is the higher energy state the electron will
immediately release heat and move to the lower excited state. TAKE HOME Electrons will always reach
the lower excited state ultimately. There is not an excited state for green (which is why chlorophyll is
green). One photon = One electron.
Fates of an electron in the excited state Heat loss (not normally in Chlamy as it functions to retain
energy), fluorescence (release of light) (fluorescence is of a slightly longer wavelength than the photon
as some energy is lost in heat), work (photochemistry, used to change a molecule), energy transfer
(passed to a neighbouring pigment)
Photochemistry Takes place in the Photoreceptor (isomerization of retinal). Photosynthesis - Takes
place in the photosystem. The chlorophyll are embedded in a protein which surrounds the photo-center.
Excited chlorophyll is denoted Chl+. Energy can be transmitted from one chlorophyll into another
(energy transfer). There is no photochemistry occurring (no electron movement, only excitation through
the antenna). Photochemistry occurs when the energy reaches the reaction center where
photochemistry takes place (oxidation of chlorophyll). The electron released through this process is used
to drive electron transport.
Rhodopsin (Retina, discs of the rod, photoreceptor) Retinal is a pigment surrounded by the protein
opsin. Retinal is unique because it when it absorbs a photon it transforms from 11-cis to all-trans. When
this conversion happens that form of the pigment detaches from the opsin. This is different than a
photosystem where the chlorophylls always stay put. This changes the opsin which can than interact
with the transducin. Once it does it activates phosphodiesterase. This enzyme cleaves a phosphate bond

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in cyclic GMP, generating 5-prime GMP, detaching it from a sodium transporter (shuts it off, no sodium
enters the cell). Consequently, the membrane hyperpolarizes
Visible Light The only light visible by humans (amphibians can view UV light). Evolution has only
allowed eyes to trap only some light wavelengths. This Is because visible light is so dominant (O3 sucks
away a lot of the ultraviolet light so it doesn’t reach Earth). Also, from an energetic point of view, visible
light is PERFECT. Other wavelengths obliterate chlorophyll.
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