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BIOL 1000 Study Guide - Midterm Guide: Symporter, Plasmid, Integral Membrane Protein


Department
Biology
Course Code
BIOL 1000
Professor
Nicole Nivillac
Study Guide
Midterm

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Learning Outcomes Biology 1000 Test One
Light and Life
Define/explain key terms: electromagnetic radiation, wavelength of light, photon, pigment,
photoreceptor, absorption spectrum, DNA, eyespot, eye [Knowledge]
Electromagnetic radiation: variable wavelength and energy; kind of radiation which includes
visible light, radio waves, gamma rays and x-rays
Wavelength of Light: distance between two peaks (measured in nanometers)
Photon: energy which can be used to do work; particle; have a precise amount of energy but no
mass; electromagnetic spectrum is made up of photons
Pigment: chemical structures (NOT made up of amino acids); pigments can look different but
have one thing in common alternating double and signal bonds aka conjugated system; it is
the natural colouring of material (pigment absorbs photon)
Photoreceptor: light sensor (light sensing structure found in almost all organisms) ex. Rhodopsin
Absorption Spectrum: all pigments have a particular wavelength they can absorb
DNA: deoxyribonucleic acid molecule that carries genetic information
Eyespot: sends signal for light (intracellular signalling); not important for vision
Eye: an organ used to sense light; important for vision; vision requires the brain to interpret
signal sent to the brain from the eye
Explain two major functions of light in living systems; compare and contrast the different ways that
light can interact with matter. [Comprehension]
When a photon hits an object, the photon has three possible fates: it can be
reflected off the object; transmitted through the object; or it can be absorbed by object
To be used as a source of energy or information by an organism, it is absorption that must take
place
Absorption occurs when the energy of the photon is transferred to an electron within a
molecule, exciting the electron and moving it from ground state to a higher energy level
referred to excited state.
1. Light as a source of energy: photosynthesis process whereby light energy is used by plants
and related organisms to convert carbon dioxide into sugars. Some organisms use light as a
proton pump
Ex. Light driven proton pump bacteriorhodopsin (certain bacteria use light as an
energy source which is not always photosynthetic)
2. Light as a source of information: senses light direction and intensity, connected to mechanisms
involved in swimming swims either away or towards the light (phototaxis)
Vision: photoreceptor (light sensing structure) is made up of pigment and protein
When light hits photoreceptor it hits the pigment first where it is absorbed,
electrons excited Pigment will change shape (cis to trans confirmation;
conformational changes) once pigment changes shape, it will cause shape
change in the protein component when protein changes shape it causes
further things to happen within the cell (signal transduction)
One of the most well known = rhodopsin (made up of retinol (pigment) and opsin
(protein) associate information with vision but not all organisms see like humans:
chlamydomonas (eukaryotic organism which contains rhodopsin but does’t see like us)
Describe the general physiology of the human eye (camera eye), cones and rods and how light is
sensed. [Comprehension]
The eye is an organ used by animals to sense light. The process of vision does not only require
the eye to absorb the light but also a brain or a simple nervous system to interpret the signals
sent from the eye. Since the detailed vision processing occurs in the brain and not the eyes it is
often said that we see with our brains not our eyes.
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Describe how organisms can sense light with and without image-forming eyes (including structure and
function of photoreceptors). [Comprehension]
Organisms such as plants, algae, invertebrate and even some bacteria can sense light without
eyes
Eyespot = light sensitive structure that is found within the chloroplast of the cell in a region very
closely associated with the cell membrane
Composed of two layers of carotenoid rich lipid globules that play a role in focusing and
directing incoming light toward the photoreceptor molecule rhodopsin
Does not play a role in photosynthesis
Allows the cell to sense light direction and intensity
Light absorption is linked to the swimming response by the signal transduction pathway
Ocellus (found in insects ex. mollusc, flatworm)
Contains a little cup like structure that is linked with about 100 photoreceptors
They are linked to some type of nervous system through the cerebral ganglia
It can detect light but cannot see like humans (in doing so it can swim towards or away
from light)
It is important for an organism like that because it will help them stay away from
predation
Compound eye
Made up of different units (called omitudium) makes a mosaic
Each one contains photoreceptors and it is linked to the nervous system via axon
The little units together create the image
How do they know this? Computer modelling (models of these types of structures) from
there they test on the organism itself
Single lens eye (ex. squids)
Contains different structures that help focus light onto structures
Describe the molecular basis of colour vision [Comprehension] and describe the outcome of missing one
or more opsins [Application]
Cone cells in the retina of the eye allow light of different wavelength to be interpreted as color in
the brain
To produce the signal for colour vision, retinal must stimulate the opsin protein but this cannot
occur which the retinal molecule is in cis-formation
When light is absorbed it causes a conformational change in retinal which causes change
in opsin which sends a signal to the brain
There are 3 types of proteins in cone cells for colour sensing, S, M, L.
S =short wavelength of blue light, M = medium wavelength for green light and L = long
wavelength for red light
The L opsin differs from the M opsin in three significant places in the amino acid
sequence
Colour-blindness = dichromatic vision only expression of S and M opsin
Describe the different detrimental effects of light on organisms [Knowledge]
Absorption of excessive light energy can result in damage that can potentially be permanent
Higher energy wavelengths like UV are of high concern
If you have photons hitting DNA it can cause mutation (ex. thymine dimer T and A
usually in this condition you get T and T) Can affect DNA transcription etc.
How do we protect ourselves? We have a pigment called melanin
Melanin absorbs UV wavelength
Max absorbance is at lower wavelength because they having more energy therefore
want buffer that pigment gives you at higher wavelength
The photoreceptor cells that line the human retina can be damaged by exposure to bright light
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