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Chapter 1

Chapter 1 – Light and Life.docx

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Matthew Smith

Chapter 1 – Light and Life  Peerwise: http://peerwise.cs.auckland.ac.nz/ o Course ID:5577 o Use your WLU ID# as your identifier Major Themes Covered in Chapter 1:  The physical nature of light  Light as a source of energy
  Light as a source of information
  Light can damage biological molecules
  Role of light in ecology and behavior
  Life in the dark
  Organisms making their own light: bioluminescence 1.1 The physical nature of light  Chlamydomonas reinhardtii is a very common form of single-celled green alga. It is an excellent example of an organism that uses light as a form of energy and information. Each cell has a huge chloroplast to process light and signal to the flagella to move to an optimal position for light absorption. The Sun:  Earth has the optimal distance from the sun allowing proper light absorption. Light then converts matter into energy. Produces electromagnetic radiation off all different wavelengths. Electromagnetic radiation:  Moves in the form of two waves, one electrical and on magnetic, which are oriented at 90 degrees to each other.  Many of the wavelengths are reflected, some do not reach the earth. Shorter wave length is higher energy (ex. Purple and blue) and longer wave length is less energy (ex. Red). What is light?  Light is the electromagnetic radiation that humans can detect with their eyes. It is a wave of discrete particles called photons. Light behaves as waves and photons.  To be used, light energy must be absorbed by molecules called pigments.  The light being absorbed is interacting with the matter. Ex light interacts with pigments in chloroplasts driving the photosynthetic process. This interaction is important.  When light is absorbed by a pigment it causes molecular changes in said pigment.  Light can be used in three ways: transmitted, absorbed, and reflected. The most important to our study is the absorbed light. Pigment Structure:  The pigment has a conjugated structure that has a commonality in every pigment; they have alternating single and double bonds in the carbon chain.  At the molecular level, there is a delocalized electrons that are free to interact with the photons from light. Absorption of light by Chlorophyll:  One or more electrons are being excited to a higher energy state.  There is not a higher energy state that green light can be promoted to. The amount of energy in the photon absorbed must match the difference in energy between the ground state and the higher energy state.  It is the absorbance of one photon can change the excitation state of one electron. Chapter 1 – Light and Life Action Spectrum:  The effectiveness of different wavelengths of light and photosynthesis.  These shorter wave lengths of light are more efficient at driving photosynthesis  Green wavelengths of light drive photosynthesis because there are more pigments then just chlorophyll 1.2 Light as a Source of Energy:  Absorption of light by a pigment results in electrons becoming excited  Represents a source of potential energy.  The pigment is converting light energy into potential energy that is then used to dive the photosynthetic process.  It is potential energy because the electron is now in a higher state of energy of which it does not wish to remain; wanting to give off energy Halobacteria:  Halobacteria can also capture light energy via a pigment molecule called retinal  The halobacteria are pick as a result of the molecule it uses to capture light energy  The defining characteristic of this bacteria is a protein call bacteriorhodopsin which holds the pigment molecule retinal  The protein absorbs photons of light and changes its structure once this absorption occurs and the electrons are promoted to a higher energy state. When the protein becomes activated by the change in structure it pumps on hydrogen ion out (causing ATP synthase) and the protein reverts back to its original structure. 1.3 Light as a Source of Information Photoreceptors:  A photoreceptor is a basic light-sensing system, found almost universally in all organisms (the most basic type at the molecular level).  Rhodopsin: Most common photoreceptor in nature o Basis of vision in animals o Also used by many other organisms o Consists of a pigment molecule (retinal) bound to a protein (opsin) o It is a membrane protein that has seven trans membrane domains o When it absorbs a photon of light it changes its state. The structural change is big enough that it activates the protein. o It is a G-protein coupled receptor  An eyespot o Sensing light without eyes o Allows sensing of light direction and intensity o Organism responds by phototaxis o The yellow globules are full of rhodopsin, serves as the photoreceptor o Senses the direction and the intensity of light o As the direction and the intensity of the light changes so do the conditions within the cell. Optimizes the amount of energy that it is receiving as an indicator of where to move Photomorphogensis  Phytoc
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