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Lecture 2

Biology 1002B Lecture Notes - Lecture 2: Electromagnetic Spectrum, Conjugated System, Photon


Department
Biology
Course Code
BIOL 1002B
Professor
Tom Haffie
Lecture
2

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Reading Outcomes
1. Characteristics of the electromagnetic spectrum
- The range of wavelengths or frequencies of electromagnetic radiation extending from gamma
rays to the longest radio waves and including visible light
2. Definition of light
- the portion of the electromagnetic spectrum that humans can detect with their eyes (visible
light 400 to 700 nm)
- Light is a source of energy that directly or indirectly sustains virtually all organisms
- light provides organisms with information about the physical world that surrounds them
3. Relationship between wavelength and energy content of a photon.
- inverse relationship
- the longer the wavelength, the lower the energy of the photons it contains
4. Definition of absorption of light.
- absorption allows the light to be used as a source of energy or information by an organism
- when the energy of the photon is transferred to an electron within a molecule
- This excites the electron, moving it from its ground state to a higher energy level (an
excited state)
- a photon can be absorbed only if the energy of the photon matches the amount of energy
needed to move the electron from its ground state to a specific excited state
5. Molecular characteristic of pigments that make them able to absorb light.
- molecules that are very efficient at absorbing photons are called pigments
- chlorophyll a: which is involved in photosynthesis
- retinal: which is involved in vision
- indigo: which is used to dye jeans
- all have a conjugated system: a region where carbon atoms are covalently bonded to each
other with alternating single and double bonds, results in the delocalization of electrons
- The number of types of photons a pigment can absorb depends on the number of high-
energy excited states they have
- A pigment’s colour is the result of photons of light that it does not absorb. Instead of being
absorbed, these photons are reflected off the pigment
6. Understanding of why biological systems only absorb visible wavelengths of the
electromagnetic spectrum
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- ultraviolet is absorbed by the ozone layer and could possibly destroy the pigments. Longer
wavelengths don't have enough energy to
excite electrons so visible light has a perfect
energy content for biological systems
Lecture 4 Outcomes
1. Structure and mechanism of function of
the Chlamydmonas eyespot.
- found between the thylakoid membranes (in
the chloroplasts)
- channelrhodopsin are light-gated ion
channels (proteins) sitting on the plasma
membrane in close proximity to the
carotenoid globules
- carotenoids globules & channelrhodopsin
make up the eyespot
- can only perceive light when it is facing it, the carotenoids amplify the light by reflecting back
onto the channelrhodopsin proteins
- Chlamy is phototactic (responsive to light)
2. Phototransduction of the eyespot signal
- Plasma membrane is polarized, neuron cells are charged, tf inside the cell has a different
electrical potential than the outside when ions (Ca+) move in, inside becomes depolarized
& causes an action potential
- signal runs from where the eyespot is to the flagella, to be interpreted by the proteins that run
the flagella
- causes flagella to move the cell
3. Structure of channelrhodopsin.
- light-gated ion channel on the plasma membrane, light triggers the opening of the gate
- proteins can’t absorb light, but channelrhodopsin is a photoreceptor, has a protein component
called opsin (can’t absorb light)
- pigment called retinal absorbs light (this pigment is always bound inside the opsin protein, the
pigment is not free)
- retinal absorbs in the blue-green area
4. Relationship between energy of photon and electron excited states to explain pigment
colour and absorption spectrum.
- the wavelengths that the pigment reflects are the colours that the pigment appears to be
- The number of types of photons a pigment can absorb depends on the number of high-
energy excited states they have
- the absorption spectra defines the wavelengths that the pigment absorbs
5. Photoisomerization
- the photon of light isomerizes the molecule (flips from trans to cis config.)
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