BIOL 1202 Lecture Notes - Lecture 1: Photosynthetic Pigment, Reactive Oxygen Species, Melanin

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27 Aug 2016
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1st YEAR BIOLOGY
LECTURE 1: Light and Life
WHAT IS LIGHT?
oIt is a source of ENERGY, and INFORMATION
oOrganisms have evolved to exploit both.
oSingle cell organism has to do everything
oIs a form of electromagnetic energy.
Light is a wave of discrete particles called PHOTONS
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. If
the energies don’t match, then the photon of light is not absorbed but instead is
transmitted through the molecule or reflected.
Light energy must be absorbed by molecules called PIGMENTS
WAVELENGTH: Distance between two successive peaks - determine color
UV rays - short wavelength, high energy
MICROWAVES - longer wavelength, low energy
Why does life preferably use visible light?
ULTRAVIOLET RADIATION (200 and 400 nm)
More energetic than visible light
Ionizes biological molecules, which affects their structures and functions
TOO ENERGETIC, it excites electrons, but can also knock electrons off atoms.
Ozone partially absorbs UV radiation, therefore not all wavelengths make it to
Earth's surface.
UV, MELANIN and SUNSCREEN
MELANIN: melanin synthesis increases when skin cells detect DNA damage caused by UV light.
Darker skin produces more melanin compared to lighter skin.
SKIN REFLECTANCE: the amount of UV light that REFLECTS OFF, rather than is absorbed by, the
skin.
It is lowest at the equator, increases towards poles.
3 TYPES OF UV LIGHT:
UV - A (315 - 400 nm)
oPenetrates into the skin where it generates reactive oxygen species
oCan lead to skin cancer
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